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Meiosis
biol 1210
| Question | Answer |
|---|---|
| gametes | reproductive cells that have half the # of chromosomes as a somatic cell (sperm & egg in animals & plants) |
| fertilization define | the fusion of gametes (full chromosome # is restored) |
| meiosis define | nuclear division that leads to halving of chromosome # |
| before meiosis | each chromosome in 2n parent cell is replicated (during S phase of interphase) - when replication finishes, each chromosome has 2 identical sister chromatids that remain attached along their entire length by cohesins |
| meiosis stages | meiosis I: 2 homologs of each chromosome pair separate into 2 daughter cells, each w 1 set of chromosomes & meiosis II: sister chromatids of each chromosome separate into 2 daughter cells (overall produces 4 haploid cells) |
| synapsis | the pairing process of homologs during prophase I |
| bivalent | the structure that results from synapsis btwn 2 homologs |
| non-sister chromatids | the chromatids of the homologs during synapsis |
| 1st & 2nd stages of synapsis & crossing over | 1. as chromosomes condense, sister chromatids r joined along entire length by cohesins 2. homologs pair by synapsis & are held together by synaptonemal complex |
| 3rd & 4th stages of synapsis & crossing over | 3. breaks are made in DNA & cross over occurs btwn corresponding segments of non-sister chromatids 4. synaptonemal complex disassembles & homologs held together only at chiasmata (partial separation) |
| chiasma | mark the sites of crossing over; where non-sister chromatids are attached during prophase I |
| prophase I events | early - chromosomes condense, spindle apparatus forms, nuclear envelope breaks down, synapsis of homologs. Late - chiasmata visible (often multiple btwn sister chromatids), partial separation |
| metaphase I events | movement of bivalents to metaphase plate |
| anaphase I events | homologs separate & move to poles of cell |
| telophase I | homologs finish moving to opposite poles, spindle apparatus disassembles |
| meiosis II | no DNA synthesis occurs between the 2 meiotic divisions (no interphase). Meiosis II resembles mitosis w the split of sister chromatids during anaphase |
| what splits in anaphase I? What splits in anaphae II? | I: homologs, II: sister chromatids |
| if a cell starts w 20 chromosomes, how many at end of meiosis I? At end of meiosis II? What is different? | I: 10 each (n), II: 10 each. Chromosomes at end of meiosis I are replicated (2 chromatids); at the end of meiosis II they are unreplicated (1 chromatid) |
| describe animal life cycle | 2n adult -> products of meiosis are (n) gametes with half chromosome # -> fertilization combines sperm (n) & egg (n) to make (2n) zygote, restoring original chromosome # -> mitosis & development grows baby |
| asexual reproduction v. sexual reproduction | asexual: produces clones that are identical to one another & parent cell, sexual: produces offspring w unique chromosome complements (shuffles alleles of the parents into the offspring) |
| results of meiosis | 4 cells with chromosome composition different from each other & from parent cells - independent shuffling of maternal & paternal chromosomes, crossing over during meiosis I, fertilization - haploid sets combine to create unique offspring |
| independent assortment | homologs orient randomly in metaphase I. Each pair of chromosomes sorts maternal & paternal homologs into daughter cells independently of other pairs |
| # of combinations possible during independent assortment | 2^n where n is haploid #. Ex. humans n = 23, 2^23 = 8.4 million possible combinations of chromosomes |
| crossing over | produces recombinant chromosomes which combine genes from each parent - homologous portions of 2 non-sister chromatids swap places & combine DNA from 2 parents into 1 chromosome |
| random fertilization | any sperm can fuse w any ovum (unfertilized egg). Ex. fusion of 2 gametes w 8.4 million possible chromosome combinations produces zygote w ~70 trillion diploid combinations |
| what leads to genetic variation during sexual reproduction? | independent assortment, crossing over & random fertilization |
| random fertilization happens during meiosis I. T/F | F. Random fertilization is NOT part of meiosis |
| what is the basis for matching homologs matched? | Size (length), centromere position, and banding pattern (chromosomes are stained w dyes that show unique patterns of light & dark bands). Homologs r identical in all of these aspects |
| how do sister chromatids stay together in meiosis I and split in meiosis II? | they r joined together along their entire length by cohesins which are protected by other proteins during meiosis I but during meiosis II the protection is removed and the cohesins are disassembled |
Created by:
AntBanana
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