Midterm Preperation Lecture 10 - Meiosis.docx

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Biological Sciences
BISC 102
Tom Haffie

Lecture 10 – Meiosis Reason why meiosis I is "reductional" and meiosis II is "equational"  Zygotes bring DNA from two different parents into the same cell. (n+n=2n)  Homologous chromosomes carry the same genes but different alleles o Homologues have the same genes in the same places  Reductional Division = during meiosis 1, the number of chromosomes is reduced from diploid to haploid, the resulting daughter cells from the parent cell are haploid. o Meiosis I cells are haploid. Its reductional division because the number of chromosomes (2n  n) but the C-value is still 2C because there’s 2 DNA molecules per chromosome.  Equational = the amount of DNA is reduced “C-value” but the number of chromosomes is not (n) o In meiosis II, the cells divide to give the daughter cells “1C” the amount of DNA per chromosome. Changes in C and n during meiosis  In meiosis 1, chromosome number is reduced from diploid to haploid (n)  In meiosis II, the cells divide to give the daughter cells “1C” the amount of DNA per chromosome.  Mechanism of recombination during prophase  In prophase of meiosis I, replicated homologues pair and recombine!  Recombination: o The enzymes make the cuts in the homologues backbones to make the crossover between those 2 chromosomes. o Recombination is mutagenic because it cuts and pastes the DNA backbones to the other chromosome of the homologue. o The switch is very precise; the switch does not cause any problems. o Role of cohesin and synaptonemal complex  Cohesin = a protein that holds chromatids together  Synaptonemal complex = protein that holds homologues chromosomes together How homolgues pair in order for all non-sister chromatids to participate in recombination Mechanism by which recombination creates new combinations of alleles  C
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