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256 Cards in this Set
- Front
- Back
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DNA is organized into?
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chromosomes
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Chromosomes serve as?
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vehicles for transmitting genetic information
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Two major processes that are involved in the genetic continuity of nucleated cells.....
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mitosis and meiosis
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Chromosome
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In prokaryotes, a DNA molecule containing the organism’s genome; In eukaryotes, a DNA molecule complexed with RNA and proteins to form a threadlike structure containing genetic information arranged in a linear sequence and visible during mitosis and meiosis.
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Mitosis
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A form of cellular reproduction producing two progeny cells, identical genetically to the progenitor cell, that is, the production of two cells from one, each with the same chromosome complement as the parent cell.
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meiosis
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The process of cell division in gametogenesis or sporogenesis during which the diploid number of chromosomes is reduced to the haploid number.
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Leads to the production of two cells, each with the same number of chromosomes as the parent cell.
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Mitosis
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Reduces the genetic content and the number of chromosomes by precisely half.
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Meiosis
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that portion of the cell cycle during which the hereditary components are equally partitioned into daughter cells
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Mitosis
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part of a special type of cell division that leads to the production of sex cells: gametes or spores. This process is an essential step in the transmission of genetic information from an organism to its offspring.
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Meiosis
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Normally, chromosomes are visible only during....
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mitosis and meiosis
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chromatin
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One of the longitudinal subunits of a replicated chromosome.
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plasma membrane
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an outer covering that defines the cell boundary and delimits the cell from its immediate external environment. This membrane is not passive but instead actively controls the movement of materials into and out of the cell.
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cell wall
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outer covering of plant cells
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major component of the cell wall
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a polysaccharide called cellulose
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cell coat
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a covering over the plasma membrane consisting of glycoproteins and polysaccharides that provides biochemical identity at the surface of cells. The components of the coat that establish cellular identity are under genetic control
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cell coat examples?
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AB, Rh, and MN antigens–are found on the surface of red blood cells. On other cell surfaces, histocompatibility antigens, which elicit an immune response during tissue and organ transplants, are present.
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histocompatibility antigens
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elicit an immune response during tissue and organ transplants
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Found on the surfaces of cells. These molecules act as recognition sites that transfer specific chemical signals across the cell membrane into the cell.
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receptor molecules
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defining characteristic of eukaryotic organisms?
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The presence of a nucleus and other membranous organelles.
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eukaryotes
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Organisms having true nuclei and membranous organelles and whose cells demonstrate mitosis and meiosis.
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nucleus
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The membrane-bound cytoplasmic organelle of eukaryotic cells that contains the chromosomes and nucleolus.
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nucleolus
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The nuclear site of ribosome biosynthesis and assembly; usually associated with or formed in association with the DNA comprising the nucleolar organizer region.
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During nondivisional phases of the cell cycle, the DNA fibers are....
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uncoiled and dispersed into chromatin
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During mitosis and meiosis, chromatin fibers.....
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coil and condense into chromosomes.
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nucleolar organizer region (NOR)
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A chromosomal region containing the genes for rRNA; most often found in physical association with the nucleolus.
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The portions of DNA that encode rRNA are collectively referred to as.....
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nucleolus organizer region, or the NOR
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An amorphous component of the nucleus where ribosomal RNA (rRNA) is synthesized and where the initial stages of ribosomal assembly occur?
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nucleolus
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lack a nuclear envelope and membranous organelles?
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Prokaryotic organisms
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prokaryotes
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Organisms lacking nuclear membranes and true chromosomes. Bacteria and blue–green algae are examples of prokaryotic organisms.
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nucleoid
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The DNA-containing region within the cytoplasm in prokaryotic cells.
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T/F: DNA in prokaryotes associated as extensively with proteins as is eukaryotic DNA
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False
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cytoplasm
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The remainder of the eukaryotic cell within the plasma membrane, excluding the nucleus. Also includes an extensive system of tubules and filaments, comprising the cytoskeleton, which provides a lattice of support structures within the cell.
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cytosol
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a nonparticulate, colloidal material in the cytoplasm that surrounds and encompasses the cellular organelles.
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cytoskeleton
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provides a lattice of support structures within the cell. Consists primarily of microtubules made of the protein tubulin and microfilaments made of the protein actin, this structural framework maintains cell shape, facilitates cell mobility, and anchors the various organelles.
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microtubules consist primarily of....
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the protein tubulin
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microfilaments are made of
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the protein actin
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Compartmentalizes the cytoplasm, greatly increasing the surface area available for biochemical synthesis....
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endoplasmic reticulum (ER)
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endoplasmic reticulum (ER)
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A membranous organelle system in the cytoplasm of eukaryotic cells. In rough ER, the outer surface of the membranes is ribosome-studded; in smooth ER, it is not.
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The ER appears smooth in places where.....
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it serves as the site for synthesizing fatty acids and phospholipids
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The ER appears rough where....
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it is studded with ribosomes.
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Ribosomes
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serve as sites where genetic information contained in messenger RNA (mRNA) is translated into proteins.
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mitochondrial DNA (mtDNA)
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Double-stranded, self-replicating circular DNA found in mitochondria that encodes mitochondrial ribosomal RNAs, transfer RNAs, and proteins used in oxidative respiratory functions of the organelle.
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Mitochondria
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found in most eukaryotes, including both animal and plant cells and are the sites of the oxidative phases of cell respiration. These chemical reactions generate large amounts of the energy-rich molecule adenosine triphosphate (ATP).
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chloroplast
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A self-replicating cytoplasmic organelle containing chlorophyll. The site of photosynthesis, the major energy-trapping process on Earth
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T/F: Both mitochondria and chloroplasts contain DNA in a form distinct from that found in the nucleus.
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True.
(They are able to duplicate themselves and transcribe and translate their own genetic information.) |
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endosymbiont theory
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The proposal that self-replicating cellular organelles such as mitochondria and chloroplasts were originally free-living organisms that entered into a symbiotic relationship with nucleated cells.
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centriole
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A cytoplasmic organelle composed of nine groups of microtubules, generally arranged in triplets. Centrioles function in the generation of cilia and flagella and serve as foci for the spindles in cell division.
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Cytoplasmic bodies, which are located in a specialized region called the centrosome, and are associated with the organization of spindle fibers that function in mitosis and meiosis.....
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centrioles
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spindle fibers
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Cytoplasmic fibrils formed during cell division that are involved with the separation of chromatids at the anaphase stage of mitosis and meiosis as well as their movement toward opposite poles in the cell.
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The organization of spindle fibers by the centrioles occurs during.....
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the early phases of mitosis and meiosis.
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Composed of arrays of microtubules consisting of polymers of the protein tubulin.....
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spindle fibers
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centromere
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The specialized heterochromatic chromosomal region at which sister chromatids remain attached after replication, and the site to which spindle fibers attach to the chromosome during cell division. Location of the centromere determines the shape of the chromosome during the anaphase portion of cell division. Also known as the primary constriction.
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Also known as the primary constriction.
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centromere
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metacentric chromosome
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A chromosome that has a centrally located centromere and therefore chromosome arms of equal lengths.
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submetacentric chromosome
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A chromosome with the centromere placed so that one arm of the chromosome is slightly longer than the other.
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acrocentric chromosome
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Chromosome with the centromere located very close to one end. Human chromosomes 13, 14, 15, 21, and 22 are acrocentric.
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telocentric chromosome
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A chromosome in which the centromere is located at its very end.
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p arm
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The shorter arm, by convention, is shown above the centromere.
(p, for “petite”) |
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q arm
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The longer arm is shown below the centromere.
(because q is the next letter in the alphabet). |
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he shape of the chromosome during anaphase is determined by.....
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the position of the centromere during metaphase.
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diploid (2n)
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A condition in which each chromosome exists in pairs; having two of each chromosome.
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T/F: All somatic cells derived from members of the same species contain an identical number of chromosomes
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True.
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homologous chromosomes
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Chromosomes that synapse or pair during meiosis and that are identical with respect to their genetic loci and centromere placement.
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T/F: Many bacteria and viruses have but one chromosome.
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True.
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karyotype
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The chromosome complement of a cell or an individual. Often used to refer to the arrangement of metaphase chromosomes in a sequence according to length and centromere position.
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human karyotype
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2n number of 46 chromosomes
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sister chromatid exchange (SCE)
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A crossing over event that can occur in meiotic and mitotic cells involving the reciprocal exchange of chromosomal material between sister chromatids joined by a common centromere. Such exchanges can be detected cytologically after BrdU is incorporated into the replicating chromosomes.
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T/F:The haploid number (n) of chromosomes is equal to twice the diploid number.
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False.
The haploid number (n) of chromosomes is equal to one-half the diploid number. |
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genome
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The set of hereditary information encoded in the DNA of an organism, including both the protein-coding and non-protein-coding sequences.
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locus
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The site or place on a chromosome where a particular gene is located. Identical in homologous chromosomes.
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allele
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One of the possible mutational forms of a gene, often distinguished from other alleles by phenotypic effects.
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Process that converts the diploid number of chromosomes to the haploid number during the formation of gametes or spores.
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meiosis
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SRY
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The sex-determining region of the Y chromosome, found near the chromosome’s pseudoautosomal boundary. Accumulated evidence indicates that this gene’s product is the testis-determining factor (TDF).
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Carry two homologous X chromosomes....
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Females
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Carry one Y chromosome in addition to one X chromosome.
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Males
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zygote
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The diploid cell produced by the fusion of haploid gametic nuclei.
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karyokinesis
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The process of nuclear division. The chromosomes must first be exactly replicated and then accurately partitioned. The end result is the production of two daughter nuclei, each with a chromosome composition identical to that of the parent cell.
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Karyokinesis is followed by.....?
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cytoplasmic division, or cytokinesis.
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cytokinesis
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The division or separation of the cytoplasm during mitosis or meiosis. It requires a mechanism that partitions the volume into two parts, then encloses each new cell in a distinct plasma membrane. As the cytoplasm is reconstituted, organelles either replicate themselves, arise from existing membrane structures, or are synthesized de novo (anew) in each cell.
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Following cell division, the initial size of each new daughter cell is....?
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approximately one-half the size of the parent cell.
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cell cycle
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The sequence of growth phases of an individual cell; divided into G1 (gap 1), S (DNA synthesis), G2 (gap 2), and M (mitosis). A cell may temporarily or permanently be withdrawn from the cell cycle, in which case it is said to enter the G0 stage. (The events that occur from the completion of one division until the completion of the next division )
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interphase
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In the cell cycle, the interval between divisions.
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S phase
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the period, during which DNA is synthesized, occurs before the cell enters mitosis
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The biochemical step critical to the ensuing mitosis that occurs during interphase?
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the replication of the DNA of each chromosome
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The stages comprising an arbitrary cell cycle?
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Following mitosis, cells enter the G1 stage of interphase, initiating a new cycle. Cells may become nondividing (G0) or continue through G1, where they become committed to begin DNA synthesis (S) and complete the cycle (G2 and mitosis). Following mitosis, two daughter cells are produced, and the cycle begins anew for both of them.
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The two periods during interphase when no DNA synthesis occurs?
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G1 (gap I) and G2 (gap II)
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What has occured by the end of G2?
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the volume of the cell has roughly doubled, DNA has been replicated, and mitosis (M) is initiated
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During both of these intervals, as well as during S, intensive metabolic activity, cell growth, and cell differentiation are evident....?
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G1 (gap I) and G2 (gap II)
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Many cell types in different organisms traverse the complete cycle in about how much time?
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16 hours.
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The actual process of mitosis occupies how much time?
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often less than an hour.
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Most variation is seen in the length of time spent in which stage/phase of the cell cycle?
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G1 stage
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G0
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A nondividing but metabolically active state that cells may enter from the G1 phase of the cell cycle.
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At a point late in G1, all cells follow one of which two paths?
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They either withdraw from the cycle, become quiescent, and enter the G0 stage, or they become committed to initiating DNA synthesis and completing the cycle. Cells that enter G0 remain viable and metabolically active but are not proliferative.
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Cytologically, interphase is characterized by what?
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the absence of visible chromosomes. Instead, the nucleus is filled with chromatin fibers that are formed as the chromosomes uncoil and disperse after the previous mitosis.
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List the stages of mitosis.
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in order of occurrence, the stages of mitosis are prophase, prometaphase, metaphase, anaphase, and telophase
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Over half of mitosis is spent in which phase?
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prophase
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The shape of the chromosome during anaphase is determined by what? the position of the centromere.
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the position of the centromere.
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Describe the human karyotype.
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23 chromosomes donated by each parent.
(Total = 46 or 23 pairs). |
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One of the early events in prophase of all animal cells is what?
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the migration of two pairs of centrioles to opposite ends of the cell.
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Where are centrioles found?
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These structures are found just outside the nuclear envelope in an area of differentiated cytoplasm called the centrosome. It is believed that each pair of centrioles consists of one mature unit and a smaller, newly formed centriole.
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Where do the centrioles migrate?
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The centrioles migrate to establish poles at opposite ends of the cell.
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After migrating, the centrioles do what?
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After migrating, the centrioles are responsible for organizing cytoplasmic microtubules into the spindle fibers that run between these poles, creating an axis along which chromosomal separation occurs.
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T/F: Centrioles are universally responsible for the organization of spindle fibers.
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False. The cells of most plants (there are a few exceptions), fungi, and certain algae seem to lack centrioles. Spindle fibers are nevertheless apparent during mitosis. Therefore, centrioles are not universally responsible for the organization of spindle fibers.
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What is apparent near the end of prophase?
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It becomes apparent near the end of prophase that each chromosome is actually a double structure split longitudinally except at a single point of constriction, the centromere.
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The two parts of each chromosome are called what?
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chromatids
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Where does the term "sister chromatids" come from?
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Because the DNA contained in each pair of chromatids represents the duplication of a single chromosome, the two chromatids are genetically identical.
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What are sister chromatids are held together by?
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a protein called cohesin. It is originally produced during the S phase of the cell cycle when the DNA of each chromosome is replicated.
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Why can't we see chromatids during interphase?
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because the chromatin is uncoiled and dispersed in the nucleus, even though the chromosomes are already double structures (although it doesn't become apparent until late prophase)
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What is the human diploid number?
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46
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What is the distinguishing event of prometaphase and metaphase?
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the migration of every chromosome, led by its centromeric region, to the equatorial plane
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what is the equatorial plane?
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also referred to as the metaphase plate, is the midline region of the cell, a plane that lies perpendicular to the axis established by the spindle fibers
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prometaphase
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refers to the period of chromosome movement. (metaphase is applied strictly to the chromosome configuration following migration)
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metaphase
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The stage of cell division in which condensed chromosomes lie in a central plane between the two poles of the cell and during which the chromosomes become attached to the spindle fibers.
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Migration of the chromosomes during metaphase is made possible by what?
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the binding of spindle fibers to the chromosome's kinetochore.
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kinetochore
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A fibrous structure with a size of about 400 nm, located within the centromere. It appears to be the site of microtubule attachment during division.
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This structure forms on opposite sides of each centromere, in intimate association with the two sister chromatids and is an assembly of multilayered plates of proteins associated with the centromere.
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kinetochore
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spindle fibers consist of?
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microtubules
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Microtubules consist of and come from what?
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Microtubules consist of the protein tubulin and seem to originate and “grow” out of the two centrosome regions (which contain the centrioles) at opposite poles of the cell. They are dynamic structures that lengthen and shorten as a result of the addition or loss of polarized tubulin subunits.
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kinetochore microtubules.
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The microtubules most directly responsible for chromosome migration that make contact with, and adhere to, kinetochores as they grow from the centrosome region. They have one end near the centrosome region (at one of the poles of the cell) and the other anchored to the kinetochore.
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Describe the completion of metaphase.
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each centromere is aligned at the metaphase plate with the chromosome arms extending outward in a random array.
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anaphase
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Stage of mitosis or meiosis in which chromosomes begin moving to opposite poles of the cell.
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The shortest stage of mitosis is which?
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anaphase
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disjunction
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The separation of chromosomes during the anaphase stage of cell division.
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For complete disjunction to occur what must happen?
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each centromeric region must split in two. This splitting signals the initiation of anaphase.
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When is each chromatid referred to as a daughter chromosome?
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After sister chromatids of each chromosome disjoin and migrate to opposite ends of the cell.
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T/F: Closely related organisms can have genomes with very different karyotypes (chromosome sizes and numbers
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True. Chromosomes from two species of Muntjac Deer.
Indian Muntjack 7 Chinese Muntjac 18 American Muntjc 46 Hybrid – Ch. X Ind. 9 |
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chromosome migration during anaphase results from what?
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chromosome migration results from the activity of a series of specific molecules called motor proteins found at several locations within the dividing cell. These proteins, described as molecular motors, use the energy generated by the hydrolysis of ATP. Their effect on the activity of microtubules serves ultimately to shorten the spindle fibers, drawing the chromosomes to opposite ends of the cell
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What is the final stage of mitosis?
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Telophase
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What is the most significant event of telophase?
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cytokinesis, the division or partitioning of the cytoplasm. Cytokinesis is essential if two new cells are to be produced from one cell.
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telophase
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The stage of cell division in which the daughter chromosomes have reached the opposite poles of the cell and reverse the stages characteristic of prophase, re-forming the nuclear envelopes and uncoiling the chromosomes. Telophase ends with the cytokinesis, which divides the cytoplasm and splits cell into two.
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What happens during cytokinesis of plant cells?
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a cell plate is synthesized and laid down across the region of the metaphase plate.
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What happens during cytokinesis of animal cells?
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Animal cells undergo a constriction of the cytoplasm, in much the way that a loop of string might be tightened around the middle of a balloon.
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middle lamella
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The cell plate laid down during telophase. Subsequently, the primary and secondary layers of the cell wall are deposited between the cell membrane and middle lamella in each of the resulting daughter cells.
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Why is cytokinesis different in plant cells?
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Plant cells, which are more regularly shaped and structurally rigid, require a mechanism for depositing new cell wall material around the plasma membrane
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cell furrow
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Characteristic of newly divided cells in animals, produced by complete constriction of the cell membrane.
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What events necessary for the transition from mitosis to interphase are initiated during late telophase?
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In each new cell, the chromosomes begin to uncoil and become diffuse chromatin once again, while the nuclear envelope reforms around them, the spindle fibers disappear, and the nucleolus gradually reforms and becomes visible in the nucleus during early interphase.
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What happens at the conclusion of telophase?
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The cell enters interphase.
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Describe interphase.
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Cells are not dividing .
Chromosomes are decondensed –Chromatin. Information is available to the cell for synthesizing products. During interphase - DNA is duplicated in S Phase Results in 4 copies of each gene instead of the normal 2 in a diploid cell. |
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Describe prophase.
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Chromatin begins to coil and condense to form chromosomes
Centrioles migrate towards opposite poles - centrosome Each chromosome appears to have two strands- Chromatids The nuclear envelope disappears The nucleolus disappears In cytoplasm, the spindle apparatus forms |
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Describe prometaphase.
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Chromosomes are visible with two chromatids attached to the centromere and migrate in the cell.
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Describe prometaphase into metaphase.
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Spindle grows and forms attachments to the chromosomes at the centromeres
Chromosomes move to an equatorial plate (metaphase plate) Chromosomes are most condensed Chromosomes can be stained – visualized and counted |
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Describe metaphase.
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Chromosomes move to the middle line region in the cell -equitorial plate.
Chromosome migration is facilitated by the binding of spindle fibers to the kinetochores. |
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Describe anaphase.
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Centromeres divide to create two chromosomes
Spindle fibers shorten and the sister chromosomes are drawn to the opposite poles Poles of the spindle apparatus are pushed apart as the cell elongates Anaphase results in the exact division of chromosome, distributing one complete diploid complement of genetic information to each daughter cell. |
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Describe telophase.
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Nuclear envelopes reassemble and surround each set of daughter. chromosomes
Nucleoli reappear inside the newly formed nuclei. Cytokinesis : In animal cell, a furrow appears around the cell that eventually pinches the cell into two new cells In plants, a cell plate forms between the two daughter nuclei as the cell wall divides the cell Chromosomes decondense in the daughter cells to become chromatin and the cells are once again in Interphase. |
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kinases
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The normal products of many mutated genes, enzymes that can add phosphates to other proteins. They serve as “master control” molecules functioning in conjunction with proteins called cyclins. Activated kinases then phosphorylate other target proteins that regulate the progress of the cell cycle.
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cyclins
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In eukaryotic cells, a class of proteins that are synthesized and degraded in synchrony with the cell cycle and regulate passage through stages of the cycle. Cyclins bind to kinases, activating them at appropriate times during the cell cycle.
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Three major checkpoints of the cell cycle.
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G1/S checkpoint, G2/M checkpoint, M checkpoint.
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G1 checkpoint
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A point in the G1 phase of the cell cycle when a cell becomes committed to initiating DNA synthesis and continuing the cycle or withdraws into the G0 resting stage. Monitors the size the cell has achieved since its previous mitosis and also evaluates the condition of the DNA. If the cell has not reached an adequate size or if the DNA has been damaged, further progress through the cycle is arrested until these conditions are “corrected.” If both conditions are “normal” at G1/S, then the cell is allowed to proceed to the S phase of the cycle.
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G2/M checkpoint
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where DNA is monitored prior to the start of mitosis. If DNA replication is incomplete or any DNA damage is detected and has not been repaired, the cell cycle is arrested.
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M checkpoint.
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Here, both the successful formation of the spindle fiber system and the attachment of spindle fibers to the kinetochores associated with the centromeres are monitored. If spindle fibers are not properly formed or attachment is inadequate, mitosis is arrested.
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haploid gametes or spores contain what?
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precisely one member of each homologous pair of chromosomes
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crossing over
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The exchange of chromosomal material (parts of chromosomal arms) between homologous chromosomes by breakage and reunion. The exchange of material between nonsister chromatids during meiosis is the basis of genetic recombination. This process creates intact chromosomes that are mosaics of the maternal and paternal homologs from which they arise, further enhancing the potential genetic variation in gametes and the offspring derived from them.
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the major source of genetic recombination within species?
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meiosis
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synapse
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when early in meiosis, homologous chromosomes form pairs.
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bivalents
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Synapsed homologous chromosomes in the first prophase of meiosis. Eventually gives rise to a tetrad.
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tetrad
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The four chromatids that make up paired homologs in the prophase of the first meiotic division. In eukaryotes with a predominant haploid stage (some algae and fungi), tetrad denotes the four haploid cells produced by a single meiotic division.
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The presence of four chromatids during meiosis demonstrates that both homologs have what?
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duplicated
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reductional division
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The chromosome division that halves the number of centromeres and thus reduces the chromosome number by half. The first division of meiosis is a reductional division. See also equational division.
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dyad
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The products of tetrad separation or disjunction at meiotic prophase I. Each dyad consists of two sister chromatids joined at the centromere.
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equational division
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A division stage where the number of centromeres is not reduced by half but where each chromosome is split into longitudinal halves that are distributed into two daughter nuclei. Chromosome division in mitosis and the second meiotic division are examples of equational divisions. See also reductional division. Here each dyad splits into two monads of one chromosome each
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What 3 events characterize Prophase I?
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1)as in mitosis, chromatin present in interphase thickens and coils into visible chromosomes.
2)unlike mitosis, members of each homologous pair of chromosomes undergo synapsis. 3) crossing over occurs between synapsed homologs. |
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What are the five substages of prophase I?
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eptonema, zygonema, pachynema, diplonema, and diakinesis
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leptotene
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The initial stage of meiotic prophase I, during which the chromosomes become visible and are often arranged with one or both ends gathered at one spot on the inner nuclear membrane (the so-called bouquet configuration).
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chromomere
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A coiled, beadlike region of a chromosome, most easily visualized during cell division. The aligned chromomeres of polytene chromosomes are responsible for their distinctive banding pattern.
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homology search
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a process which precedes and is essential to the initial pairing of homologs, begins during leptonema.
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zygotene
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A stage of meiotic prophase I in which the homologous chromosomes synapse and pair along their entire length, forming bivalents. The synaptonemal complex forms at this stage. The chromosomes continue to shorten and thicken during the zygotene st
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The rough-pairing of the homology search is completed by which point?
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rough pairing is complete by the end of zygonema
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synaptonemal complex (SC)
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An organelle consisting of a tripartite nucleoprotein ribbon that forms between the paired homologous chromosomes in the pachytene stage of the first meiotic division.
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When are paired homologs referred to as bivalents?
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At the end of zygonema.Although both members of each bivalent have already replicated their DNA, it is not yet visually apparent that each member is a double structure
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T/F: The number of bivalents in each species is equal to the haploid (n) number.
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True.
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pachytene
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The stage in meiotic prophase I when the synapsed homologous chromosomes split longitudinally (except at the centromere), producing a group of four chromatids called a tetrad.the chromosomes continue to coil and shorten, and further development of the synaptonemal complex occurs between the two members of each bivalent. This leads to synapsis, a more intimate pairing.
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Each bivalent contains how many chromatids?
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4
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nonsister chromatids
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chromatids from maternal and paternal members of a homologous pair
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tetrad
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The four-membered structure that contains two pairs of sister chromatids.
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diplotene
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The stage of meiotic prophase I immediately following pachytene. In diplotene, the sister chromatids begin to separate, and chiasmata become visible. These cross-like overlaps move toward the ends of the chromatids (terminalization). Within each tetrad, each pair of sister chromatids begins to separate.
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chiasma (pl., chiasmata)
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The crossed strands of nonsister chromatids seen in diplotene of the first meiotic division. Regarded as the cytological evidence for exchange of chromosomal material, or crossing over.
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T/F: The results of crossing-over are visible immediately.
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False. Although the physical exchange between chromosome areas occurred during the previous pachytene stage, the result of crossing over is visible only when the duplicated chromosomes begin to separate.
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diakinesis
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The final stage of meiotic prophase I, in which the chromosomes become tightly coiled and compacted and move toward the periphery of the nucleus. This process of terminalization begins in late diplonema and is completed during diakinesis.
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terminalization
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The movement of chiasmata toward the ends of chromosomes during the diplotene stage of the first meiotic division. During this final substage, the nucleolus and nuclear envelope break down, and the two centromeres of each tetrad attach to the recently formed spindle fibers.
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How many chromosomes present after 1st Meiotic division?
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After 1 division - 23 double stranded chromosomes (n)
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How many chromosomes present after 2nd Meiotic division?
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After 2nd division - 23 single stranded chromosomes (n)
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metaphase I
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the first division where the chromosomes have maximally shortened and thickened. The terminal chiasmata of each tetrad are visible and appear to be the only factor holding the nonsister chromatids together. Each tetrad interacts with spindle fibers, facilitating its movement to the metaphase plate. The alignment of each tetrad prior to the first anaphase is random: half of the tetrad will be pulled to one or the other pole, and the other half moves to the opposite pole.
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Which organelle is responsible for generating cellular energy in the form of ATP?
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Mitochondrion
The mitochondrion is the site where the chemical energy in glucose and other molecules is harvested to produce ATP |
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Which cell structures are directly involved in protein synthesis?
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Rough endoplasmic reticulum and ribosomes
Ribosomes are the sites of protein translation, and some ribosomes attach to the rough endoplasmic reticulum. |
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Which cell structures is involved in lipid synthesis?
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smooth ER
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T/F: A telocentric chromosome has its centromere located very close to, but not on, the end of the chromosome.
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False. An acrocentric chromosome has its centromere located very close to the end of the chromosome; a telocentric centromere is located at the very end of the chromosome.
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Cells that are metabolically active but are not destined to proliferate are said to be in what?
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G0 phase
When cells are in G0, they have withdrawn from the cell cycle and do not proliferate. |
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the phase during which DNA replication takes place?
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S Phase
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the phase during which cells get bigger and prepare to divide?
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G2
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When is DNA duplicated for cell division?
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During the S period of interphase.
Cells duplicate their DNA during S phase of the cell cycle. |
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T/F:The primary differences observed for plant cell mitosis relative to animal cell mitosis occur during telophase.
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True. During telophase, plant cells synthesize a cell plate that is laid down across the region of the metaphase plate.
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In humans, what is a fundamental difference between the production of female gametes and male gametes?
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The production of female gametes involves an unequal division of cytoplasm.
During the production of female gametes, one daughter cell contains most of the cytoplasm and one polar body contains only a small amount of cytoplasm. Thus, female gametes are 400 times larger than sperm. |
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anaphase I
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The stage in the first meiotic division during which members of homologous pairs of chromosomes separate from one another. one-half of each tetrad (a dyad) is pulled toward each pole of the dividing cell. This separation process is the physical basis of disjunction, the separation of homologous chromosomes from one another.
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nondisjunction
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A cell division error in which homologous chromosomes (in meiosis) or the sister chromatids (in mitosis) fail to separate and migrate to opposite poles; responsible for defects such as monosomy and trisomy.
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What are the conditions at the completion of the normal anaphase I?
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a series of dyads equal to the haploid number is present at each pole.
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telophase I
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The stage in the first meiotic division when duplicated chromosomes reach the poles of the dividing cell. In general, meiotic telophase is much shorter than the corresponding stage in mitosis.
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Describe Prophase I.
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Early Prophase- Homologs Pair, Crossing Over Occurs
Late Prophase- Chromosomes Condense, Spindle Forms, Nuclear Envelope Fragments |
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Describe Metaphase I.
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Homolog pairs align along the equator of the cell.
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Describe Anaphase I.
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Homologs separate and move to opposite poles.
Sister chromatids remain attached at their centromeres. |
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Describe Telophase I.
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Nuclear envelopes reassemble.
Spindle disappears. Cytokinesis divides cell into two. |
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prophase II
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each dyad is composed of one pair of sister chromatids attached by a common centromere. Nuclear envelope fragments. Spindle forms
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metaphase II
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the centromeres are positioned on the equatorial plate.
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anaphase II
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initiated when centromeres at the equatorial plate divide and the sister chromatids of each dyad are pulled to opposite poles.
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telophase II
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Nuclear envelope assembles.
Chromosomes decondense Spindle disappears Cytokinesis divides cell into two |
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Describe the results of meiosis.
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Four Gametes, Haploid cells, One copy of each chromosome, One allele of each gene, Different combinations of alleles for different genes along the chromosome
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Spermatogenesis
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Stem cells in testes divide mitotically to create a pool of spermatocytes.
Meiosis produces four spermatids, forming the mature sperm. takes place in the testes, the male reproductive organs. The process begins with the enlargement of an undifferentiated diploid germ cell called a spermatogonium. |
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spermatogonium.
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an undifferentiated diploid germ cell that grows to become a primary spermatocyte
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primary spermatocyte
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undergoes the first meiotic division to become a secondary spermatocyte
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secondary spermatocytes
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contain a haploid number of dyads. undergo meiosis II, and each of these cells produces two haploid spermatids.
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spermatids
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haploid resultants of secondary spermatocyte meiosis II
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spermiogenesis
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when spermatids go through a series of developmental changes to become highly specialized, motile spermatozoa, or sperm
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T/F: All sperm cells produced during spermatogenesis contain the haploid number of chromosomes and equal amounts of cytoplasm.
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True.
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oogenisis
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One of four meiotic products becomes an ovum.
The three remaining meiotic products are polar bodies. the formation of ova (sing. ovum), or eggs, occurs in the ovaries, the female reproductive organs. |
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T/F: The daughter cells resulting from the two meiotic divisions of oogenesis receive equal amounts of genetic material and cytoplasm.
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False. The daughter cells resulting from the two meiotic divisions of this process receive equal amounts of genetic material, but they do not receive equal amounts of cytoplasm. Instead, during each division, almost all the cytoplasm of the primary oocyte, itself derived from the oogonium, is concentrated in one of the two daughter cells. The concentration of cytoplasm is necessary because a major function of the mature ovum is to nourish the developing embryo following fertilization.
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polar body
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Produced in females at either the first or second meiotic division of gametogenesis, a discarded cell that contains one of the nuclei of the division process, but almost no cytoplasm as a result of an unequal cytokinesis.
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first polar body
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the first polar body may or may not divide again to produce two small haploid cells. The other daughter cell produced by this first meiotic division contains most of the cytoplasm and is called the secondary oocyte
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ootid
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differentiates into the mature ovum.
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secondary oocyte
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contains most of the cytoplasm. The mature ovum will be produced from the secondary oocyte during the second meiotic division.
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T/F: In humans, oogenesis in continuous.
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False. In humans the first division of all oocytes begins in the embryonic ovary but arrests in prophase I. Many years later, meiosis resumes in each oocyte just prior to its ovulation. The second division is completed only after fertilization.
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Meiosis II in the ovum is completed when?
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at the time of fertilization forming one ovum and one polar body.
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What is the predominant stage of the fungi life cycle?
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In fungi, the predominant stage of the life cycle consists of haploid vegetative cells. They arise through meiosis and proliferate by mitotic cell division.
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Processes that bridge two phases of the plant lifecycle?
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meiosis and fertilization
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folded-fiber model
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A model of eukaryotic chromosome organization in which each sister chromatid consists of a single chromatin fiber composed of double-stranded DNA and proteins wound like a tightly coiled skein of yarn.
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T/F: During Meiosis the chromosome number is doubled.
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False. The chromosome number is doubled prior to meiosis during interphase. Therefore, DNA replication is not a part of meiosis.
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T/F: During Meiosis two identical cells are produced.
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False. Four genetically unique cells are produced during meiosis. Two identical cells are produced during mitosis.
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T/F: During Meiosis the chromosome number stays the same.
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False. If this occurred during the formation of the sex cells, the next generation would have twice as many chromosomes
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T/F: During Meiosis the chromosome number is reduced by one-half.
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True. Meiosis produces gametes, which fuse to form zygotes that have the original number of chromosomes present before meiosis. This can happen only if gametes contain one-half the number of chromosomes as the zygote.
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T/F: During leptonema is the time of most intimate pairing, called synapsis.
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False. . Synapsis occurs during pachynema of prophase I.
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T/F: During leptonema is the period when the chromatin begins to condense.
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True. Leptonema is the first portion of prophase I, when the diffuse chromatin material in the nucleus begins to condense and chromosomes first become visible under a microscope
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T/F: During leptonema corresponds to the first or reductional division in meiosis.
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False. Chromatids do not divide during prophase I.
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T/F: During leptonema is the time when crossing over takes place, although this will not be apparent until later stages.
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False. Crossing over occurs during pachynema of prophase I.
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Crossing over refers to...?
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Genetic exchange between nonsister chromatids during meiosis.
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In humans, what is a fundamental difference between the production of female gametes and male gametes?
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The production of female gametes involves an unequal division of cytoplasm. During the production of female gametes, one daughter cell contains most of the cytoplasm and one polar body contains only a small amount of cytoplasm. Thus, female gametes are 400 times larger than sperm
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Which stage of meiosis enhances genetic variability among gametes?
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Prophase I
Crossing over and recombination occur during prophase I. |
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During which stage of the cell cycle are individual chromosomes not visible within cells?
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Interphase/S phase
Chromosomes are visible during most of mitosis but are present as diffuse chromatin during interphase. |
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T/F: Meiosis eventually results in the formation of gametes.
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True. meiosis only occurs in the gonads where sperm and eggs are produced.
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T/F: In mitosis the daughter cells are haploid, whereas in meiosis the daughter cells are diploid.
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False. Meiosis produces haploid gametes, mitosis produces diploid somatic cells.
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T/F: In meiosis, but not mitosis, there is a reduction in the amount of genetic material in the daughter cells.
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True. meiosis, not mitosis, is described as a reduction division.
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T/F: In mitosis, but not meiosis, the daughter cells are identical copies of the mother cell.
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True. in meiosis, gametes with completely new combinations of alleles are produced.
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T/F: Homologous chromosomes pair up and undergo recombination during prophase of mitosis.
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False. Crossing over and recombination occur only during meiosis.
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T/F: Homologous chromosomes contain all of the same genes but not necessarily the same alleles.
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True. One copy may contain the allele for blue eyes, the other for brown eyes; both are the eye-color genes, but they may be different alleles.
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T/F: In each cell, there are two pairs of homologous chromosomes—one pair from each parent.
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False. Each parent contributes a single copy, not a pair, for each chromosome.
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T/F: Homologous chromosomes are identical sequences of base pairs.
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False. Homologous chromosomes come from different parents and so may carry different alleles.
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At which phase of the cell cycle would a cell normally check for the integrity of its DNA?
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G1/S and G2/M phases
The G1/S checkpoint monitors cell size and checks for damaged DNA. The G2/M checkpoint monitors whether DNA replication and repair to any damaged DNA has been completed. Both are likely to arrest the cell cycle if they detect damaged DNA. |
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How many tetrads are found in meiotic prophase in an organism with a diploid number of 12?
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6
Each set of homologous chromosomes will pair to form the tetrads. If the diploid number is 12, there are actually 6 different chromosomes, which will be replicated and then pair up to form the tetrads. Tetrads are formed when homologous chromosomes synapse. |
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How many chromatids would be present in a human cell during prophase I of meiosis?
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92
Each of the 46 chromosomes has replicated at this point, and each chromosome is composed of 2 chromatids. Chromosomes are replicated before meiosis begins. |
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In an organism with a diploid number of 4, how many chromatids are aligned in the equatorial plane of a cell during metaphase II?
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4
Meiosis I reduces the chromosome number from 4 to 2, so each replicated chromosome has 2 chromatids each. |
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How does recombination produce gametes of almost infinite variety?
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By causing exchange of alleles between homologous chromosomes
Chromosomes with unique combinations of alleles are created by exchanging random alleles between homologs. Recombination, also called crossing over, produces the tetrads observable during prophase I of meiosis. |
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Why do the chromosomes of a mitotic cell look like X’s under a microscope if they are linear strands?
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Each linear strand has replicated during interphase.
The X-shaped structure is actually two identical strands of DNA (sister chromatids) linked at the centromere. Chromosomes are visible only during cell division after they've replicated. |
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During which stage can cells either exit the cell cycle or become committed to completing the cell cycle?
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G1
Cells can exit the cell cycle and enter G0 or be committed to initiate DNA synthesis late in G1. Cells that withdraw from the cell cycle are said to enter the G0 stage. |
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T/F: A dyad is composed of two homologous chromosomes joined at a common centromere
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False. A dyad is composed of two sister chromatids joined at a common centromere. One chromosome in a homologous pair is inherited paternally and the other is inherited maternally.
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T/F: A tetrad is composed of one pair of homologous chromosomes at synapsis of prophase I.
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True. Chromosomes are duplicated during interphase; at synapsis of prophase I, one chromosome (with two chromatids) in a tetrad is paternally inherited while the other is maternally inherited. Tetrads contain two pairs of sister chromatids.
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A cell has 16 chromosomes. How many chromosomes would its daughter cells have after meiosis?
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8
Meiosis reduces the number of chromosomes passed on to daughter cells by one-half. |
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When do sister chromatids separate during meiosis?
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Anaphase II
Sister chromatids from each dyad separate during anaphase II. |
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Which condition is evaluated at the G2/M checkpoint?
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Precise replication of DNA
A cell checks for precise replication of DNA at the G2/M checkpoint. |
