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
Equational = the amount of DNA is reduced “C-value” but the number of chromosomes is not
o In meiosis II, the cells divide to give the daughter cells “1C” the amount of DNA per
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
Mechanism of recombination during prophase
In prophase of meiosis I, replicated homologues pair and recombine!
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.
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