Genetics Exam I

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prokaryote

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unicellular organism with a simple cell structure; include eubacteria and archaea.

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eukaryote

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organism with a complex cell structure including a nuclear envelope and membrane-bound organelles; one of the three primary divisions of life, they include unicellular and multicellular forms.

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nucleus

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space in eukaryotic cells that is enclosed by the nuclear envelope and contains the chromosomes.

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histone

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low-molecular-weight protein found in eukaryotes that complexes with DNA to form chromosomes.

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chromatin

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material found in the eukaryotic nucleus; consists of DNA and proteins.

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homologous pair

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two chromosomes that are alike in structure and size and that carry genetic information for the same set of hereditary characteristics; one chromosome of a homologous pair is inherited from the male parent and the other is inherited from the female parent.

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diploid

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possessing two sets of chromosomes (two genomes).

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haploid

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possessing a single set of chromosomes (one genome).

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telomere

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stable end of a chromosome.

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origin of replication

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site where DNA synthesis is initiated.

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sister chromatid

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two copies of a chromosome that are held together at the centromere; each chromatid consists of a single DNA molecule.

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cell cycle

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stages through which a cell passes from one cell division to the next.

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checkpoint

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a key transition point at which progression to the next stage in the cell cycle is regulated.

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interphase M phase

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period in the cell cycle between the cell divisions; the cell grows, develops, and prepares for cell division.

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mitosis

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process by which the nucleus of a eukaryotic cell divides.

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cytokinesis

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process by which the cytoplasm of a cell divides.

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prophase

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stage of mitosis; the chromosomes contract and become visible, the cytoskeleton breaks down, and the mitotic spindle begins to form.

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metaphase

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stage of mitosis; chromosomes align in the center of the cell.

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anaphase

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stage of mitosis in which chromatids separate and move toward the spindle poles.

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telophase

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stage of mitosis; the chromosomes arrive at the spindle poles, the nuclear membrane re-forms, and the chromosomes relax and lengthen.

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meiosis

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process in which chromosomes of a eukaryotic cell divide to give rise to haploid reproductive cells; consists of two divisions.

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gametogenensis

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the process in which cells undergo meiosis to form gametes.

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fertilization

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fusion of gametes (sex cells) to form a zygote.

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prophase I

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stage of meiosis; chromosomes condense and pair, crossing over takes place, the nuclear membrane breaks down, and the spindle forms.

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synapsis

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close pairing of homologous chromosomes.

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bivalent

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refers to synapsed pair of homologous chromosomes.

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tetrad

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the four products of meiosis; all four chromatids of a homologous pair of chromosomes.

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crossing over

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exchange of genetic material between homologous but nonsister chromatids.

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metaphase I

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stage of meiosis; homologous pairs of chromosomes align in the center of the cell.

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anaphase I

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stage of meiosis; homologous chromosomes separate and move toward the spindle poles.

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telophase I

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stage of meiosis; chromosomes arrive at the spindle poles.

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interkinesis

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period between meiosis I and meiosis II.

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prophase II

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stage of meiosis; chromosomes condense, the nuclear membrane breaks down, and the spindle forms.

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metaphase II

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stage of meiosis; individual chromosomes align in the center of the cell.

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anaphase II

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stage of meiosis; chromatids separate and move toward the spindle poles.

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telophase II

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stage of meiosis; chromosomes arrive at the spindle poles.

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recombination

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process that produces new combinations of alleles.

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cohesin

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molecule that holds the two sister chromatids together; the breakdown of this at the centromeres enables the chromatids to separate in anaphase of meiosis and anaphase II of meiosis.

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spermatogenesis

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sperm production in animals.

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oogenesis

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egg production in animals.

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oocyte

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a female gametocyte.

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metacentric

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chromosome in which the two chromosome arms are approximately the same length.

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submetacentric

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chromosome in which the centromere is displaced toward one end, producing a short arm and a long arm.

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acrocentric

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chromosome in which the centromere is near one end, producing a long arm at one end and a knob, or satellite, at the other end.

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telocentric

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chromosome in which the centromere is at or very near one end.

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sex

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male or female.

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sex determination

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specification of sex (male or female); mechanisms include chromosomal, genic, and environmental.

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sex chromosome

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chromosomes that differ morphologically or in number in males and females.

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autosome

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chromosome that is the same in males and females; nonsex chromosome.

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heterogametic sex

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the sex (male or female) that produces two types of gametes with respect to sex chromosomes.

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homogametic sex

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the sex (male or female) that produces gametes that are all alike with regard to sex chromosomes.

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pseudoautosomal region

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small region of the X and Y chromosomes that contains homologous gene sequences.

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Turner Syndrome

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human condition in which cells contain a single X chromosome and no Y chromosome (XO); persons with this are female in appearance but do not undergo puberty and have poorly developed female secondary sex characteristics; most are sterile but have normal intelligence.

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Klinefelter Syndrome

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human condition in which cells contain one or more Y chromosomes along with multiple X chromosomes (most commonly XXY but may also be XXXY, XXXXY, or XXYY); persons with this are male in appearance but frequently possess small testes, some breast enlargement, and reduced facial and pubic hair; often taller than normal and sterile, most have normal intelligence.

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sex-determining region Y (SRY gene)

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on the Y chromosome , a gene that triggers male development.

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sex-linked characteristic

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characteristics determined by a gene or genes on sex chromosomes.

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X-linked characteristic

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characteristic determined by a gene or genes on the X chromosome.

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Y-linked characteristic

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characteristic determined by a gene or genes on the Y chromosome.

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hemizygosity

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possession of a single allele at a locus; males of organisms with XX-XY sex determination show this for X-linked loci because their cells possess a single X chromosome.

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nondisjunction

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failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis.

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dosage compensation

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equalization in males and females of the amount of protein produced by X-linked genes; in placental mammals, this is accomplished by the random inactivation of one X chromosome in the cells of females.

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Barr body

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condensed, darkly staining structure that is found in most cells of female placental mammals and is an inactivated X chromosome.

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chromosome mutation

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difference from the wild type in the number or structure of one or more chromosomes; often affects many genes and has large phenotypic effects.

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chromosome rearrangement

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change from the wild type in the structure of one or more chromosomes.

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chromosome duplication

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mutation that doubles a segment of a chromosome.

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chromosome deletion

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loss of a chromosome segment.

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pseudodominance

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expression of a normally recessive allele owing to a deletion on the homologous chromosome.

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haploinsufficient gene

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must be present in two copies for normal function; if one copy of the gene is missing, a mutant phenotype is produced.

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chromosome inversion

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rearrangement in which a segment of a chromosome has been inverted 180 degrees.

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pericentric inversion

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chromosome inversion that includes the centromere in the inverted region.

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paracentric inversion

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chromosome inversion that does not include the centromere in the inverted region.

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position effect

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dependence of the expression of a gene on the gene's location in the genome.

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translocation

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movement of a chromosome segment to a nonhomologous chromosome or to a region within the same chromosome; movement of a ribosome along mRNA in the course of translation.

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nonreciprocal translocation

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movement of a chromosome segment to a nonhomologous chromosome or region without any (or with unequal) reciprocal exchange of segments.

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reciprocal translocation

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reciprocal exchange of segments between two nonhomologous chromosomes.

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Robertsonian translocation

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translocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, resulting in a chromosome with two long arms and usually another chromosome with two short arms.

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aneuploidy

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change from the wild type in the number of chromosomes; most often an increase or decrease of one or two chromosomes.

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polyploidy

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possession of more than two haploid sets of chromosomes.

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nullisomy

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absence of both chromosomes of a homologous pair (2n-2).

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monosomy

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absence of one of the chromosomes of a homologous pair.

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trisomy

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presence of an additional copy of a chromosome (2n+1).

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tetrasomy

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presence of two extra copies of a chromosome (2n+2).

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Down syndrome (trisomy 21)

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characterized by variable degrees of mental retardation, characteristic facial features, some retardation of growth and development, and an increased incidence of heart defects, leukemia, and other abnormalities; caused by the duplication of all or part of chromosome 21.

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translocation carrier

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individual organism heterozygous for a chromosome translocation.

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uniparental disomy

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inheritance of both chromosomes of a homologous pair from a single parent.

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mosaicism

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condition in which regions of tissue within a single individual have different chromosome constitutions.

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gene

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genetic factor that helps determine a trait; often defined at the molecular level as a DNA sequence that is transcribed into an RNA molecule.