Genetics Defs - Exam 1

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synapse

Back 1

pairs of homologous chromosomes

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bivalent

Back 2

two sister chromatids

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Tetrad

Back 3

four sister chromosomes together

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dyad

Back 4

half of a tetrad

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monad

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a single chromosome

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Leptonema

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Stage in prophase 1 where chromatin material begins to condense and form chromomeres

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chromomeres

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localized condensations that resemble beads on a string. Used in homology search later in prophase

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Zygonema

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a continuation of the shortening and thickening process. Chromomeres undergo initial alignment. Synaptonemal complex begins to form

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Pachynema

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synaptonemal complex continues to develop, leading to synapsis. Evidence of the double structure is visually apparent now.

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Diplonema

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Within each tetrad, each pair of sister chromatids begins to separate. Some areas remain in contact, called chiasma. This is thought to be where crossing over occurs.

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Diakinesis

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chromosomes pull farther apart, but still loosly associated at chiasmata. Chiasmata move closer to the ends of the tetrad. Terminalization begins in late diplonema and is completed during diakinesis. Nucleolus and nuclear membrane begins to dissolve and spindle fibers begin to attach to kinetochores

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Karyotype

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a pictorial representation of all of an organisms chromosomes lined up and with homologous pairs together if diploid.

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Interphase

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the phase of cell growth and development. DNA replicated in the middle of interphase. Three checkpoints are passed during interphase: G1/S, G2/M, and M checkpoints

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Kinetochore

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The point at which spindle fibers attach to chromosomes. An assembly of multilayered proteins associated with the centromere.

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Spindle checkpoint

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AKA M checkpoint. Point that makes sure DNA has been copied faithfully and that spindle fibers have been associated with kinetochores. Controlled by spindle checkpoint genes.

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Sister chromatids

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Replica chromatids which are bound by a centromere

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Cell Cycle Checkpoint

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Set of checkpoints designed to ensure that certain replication processes are complete before the cell cycle is allowed to continue. Proteins known as cyclins along with cyclin-dependent kinases work to control the cell cycle by their concentration values.

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Homologs

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A pair of chromosomes which encode for the same function, each originating from one parent

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Bivalents

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one of a pair of synapsed homologous chromosomes

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Tetrad

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During meiosis, two pairs of sister chromatids which have been synapsed. Four chromatids in total

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Chiasmata

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Occurs durring Diplonema. An area in a synapse where chromatids remain intertwined

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Nondisjunction

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Occurs when one or more chromatids are not separated during mitosis or meiosis, resulting in more or less than normal chromosomes in a cell. Can cause genetic diseases in embryos when occurring during meiosis.

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Synaptonemal complex

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Forms during Zygonema. The ultrastructural component of the sunapse

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Synapsis

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A more intimate pairing of chromosomes during Pachynema. Chromosomes are separated by only 100nm

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Somatic Cell

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A cell which is part of the regular body. Usually already determined to become one kind of tissue type.

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Gamates

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haploid sex cells

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Gene classes important in cell division (name at least 5)

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Spindle checkpoint genes
kinetochore structure genes
spindle formation genes
DNA damage genes
Cyclins
Chromatin condensation genes
Centriole formation genes
Nuclear membrane breakdown/formation genes
Cytokinesis genes

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Monohybrid Cross

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A cross between two true-breeding individuals, selecting for a single inheritable trait

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Dihybrid Cross

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A cross between two true-breeding individuals, selecting for two inheritable traits

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Test Cross

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a method to determine the hetero or homozygocity of an individual expressing a dominant trait

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Dominant trait

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A trait which only requires one allele to be expressed that prevents the recessive allele from being expressed

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Recessive trait

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A trait which requires a homozygous set of alleles in order to be expressed

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Unit Factor

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Mendel thought that there must be some kind of discrete unit of heredity, which he called a Unit Factor, which allowed the inheritance traits to be inherited in the manner which he saw in his pea plant experiments

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Complementation analysis

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Allows for researchers to see if two independently isolated mutations are in the same gene. Two mutant strains are crossed. If the F1 generation does not exhibit the recessive mutant trait, then the genes are located on two different loci. If they still exhibit the trait, the gene is on the same loci

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Pleiotropy

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a single gene that affects several phenotypic traits

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Epistasis

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Interaction between genes such that one gene or gene pair masks or modifies the effect of another gene or gene pair (Example hh masks the expression of IA and IB)

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Spontaneous mutation

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The occurrence of mutations in the absence of known mutagens

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Conditional allele

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An allele who's expression depends on environmental factors

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Lethal allele

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An allele which, if present and active, results in the acute or eventual death of the organism

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Locus heterogeneity

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A single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci

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nucleotide

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Building blocks of DNA. Consists of a nitrogenous base, pentose sugar, and a phosphate group. Or a nucleoside attached to a phosphate group

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nucleoside

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purine or pyrimidine covalently linked to a ribose or deoxyribose

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Hydrogen Bond

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a polar bond formed between an highly electronegative atom on one molecule and a hydrogen on another molecule.

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Phosphodiester bond

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bonds that form the backbone of a single strand of DNA. Forms between the 5' end of one molecule (phosphate group) and the 3' end of the sugar on the next molecule

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Pyrimidine

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A single ring nitrogenous base

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purine

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a two ringed nucleotide base

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haploid

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only one set of chromosomes present

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diploid

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two sets of chromosomes present

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autosome

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a non-sex chromosome

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gene

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a heredity unit which encodes for a particular trait or set of traits

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allele

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a version of a gene which codes for one version of a trait

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phenotype

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the physical manifestation of a genotype

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mutation

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a random change in a gene producing a new allele which may or may not affect phenotype

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denature

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the unfolding of a protein due to unfavorable conditions

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recombinant

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genes which can be cut apart and rejoined in new ways

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genetic map

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a measure of where genes are on chromosomes with relation to each other

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interference

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the inhibition of one crossover event by a nearby crossover event

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map unit

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a relative measure of distance between two genes, measured by their percent of crossovers