Term
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Definition
- Prophase: chrom. cond, begin formation of mitotic spindle, centrosomes form foci from which MTs radiate and move to poles
- Prometaphase: nuc membrane breaks up, chroms attach to by kinetochores to MTs of mitotic spindle
- Metaphase: max condensation at equatorial plane
- Anaphase: chroms separate, sis chromatids move to opposite poles
- Telophase: decondense, nuc membrane forms around 2 dghtr nuclei
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Term
| Stages of meiosis prophase I |
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Definition
- leptotene: condense, sis chromatids so closely aligned that they cannot be distinguished
- zygotene: homolog. chroms. align along length (synapsis), corresponding DNA seq. align, held together by synaptonemal complex
- pachytene: chroms much more tightly coiled, tetrads, crossing over
- diplotene: synaptonemal complex breaks down, bivalents begin to separate but are held together by chiasmata
- diakinesis: maximal condensation
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Term
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Definition
- Nuclear membrane disappears, spindle forms, paired chroms align on equatorial plane
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Term
| meiosis Anaphase I and telophase I |
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Definition
- disjunction: 2 members of bivalent move apart and their respective centromeres with attached sis chromatids move to opp poles
- chromosome # is halved
- telophase: two haploid sets of chromosomes grouped at opposite poles
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Term
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Definition
- same stages as meiosis I
- 2 dghtr cells from meiosis I divide to give 4 haploid cells each containing 23 chromosomes
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Term
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Definition
- begins at 12 wks gestation and arrests at 20 wks in diplotene of meiosis I
- 1st division completed at ovulation
- 2nd division completed at fertilization
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Term
| 2 ways that meiosis contributes to genetic diversity |
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Definition
- indep. assortment of maternal and paternal chromosomes at anaphase I
- recombination of paternal and maternal chromosomes in prophase I (pachytene)
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Term
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Definition
- recombination in mitosis, very rare
- fxns in DNA repair
- recomb. bet. non-homologous sister chromatids can lead to areas of homozygous recessive state
- Can be involved in initiating cancer if WT allele codes for tumor suppressor gene
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Term
| site-specific recombination |
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Definition
- integration of DNA from other species (viral, bacterial) into genome at specific sites
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Term
| cohesins (fxn, structure, what about females?) |
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Definition
- multi-subunit complex (ring) assembled during S phase and degraded at anaphase forms physical connections bet sis chroms in mitosis + meiosis (sister centromeres)
- ATP hydrolysis causes openin/closing of ring
- essential for proper segregation in meiosis
- sites of chrom recomb and cohesins bet arms lock homologs together until anaphase I
- degredation of cohesins except at kinetochores allowing homologues to separate
- cohesin remaining bet sis chromatids and kinetochores is lost allowing sisters to separate at anaphase II
- in females, S phase is during development and cell division occurs when ovulated - cohesins must fxn for a long time - could be trouble
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Term
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Definition
- forms bet homologous chroms (2 pairs of sis chromatids) during MEIOSIS only
- mediates chrom pairing + provides scaffold for recomb
- 2 barrels with a zipper
- in prophase I: leptotene, SC forms; zygotene, zips; pachytene, locked; diplotene, dissociates but held at recomb sites
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Term
| Temporal aspects of recomb and synapsis in meiotic prophase I |
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Definition
- Leptotene: programmed DSBs
- zygotene: homology search bet homologous chroms + initiation of synapsis
- mid-zygotene thru pachytene: completion of synapsis and repair of DSBs
- Diplotene: desynapsis of homologous chroms except at chiasmata
- Diakinesis: condensation of chroms, chiasmata remain, all four chromatids become visible
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Term
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Definition
- DNA mismatch repair enzyme involved in formation or processing of recombination events
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Term
| Lyon hypothesis (Lyonization, x-inactivation) |
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Definition
- in fems, on x chrom is inactivated in each somatic cell
- dosage compensation (males only have 1 x chrom)
- occurs ~30 cell stage in development and is fixed - either maternal or paternal x is inactivated in all cells arising from that point
- randomly determined but fixed
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Term
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Definition
- X inactive specific transcript gene: on q arm of x,
- RNAi is transcribed and binds to x that transcribed it
- methylation and histone deacetylation attract chromosomal proteins which bind and inactivate
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