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Lecture 10

Lecture 10 Lecture Outcomes word.doc

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Western University
Biology 1001A

Lecture 10 Lecture Outcomes 1. Reason why meiosis I is "reductional" and meiosis II is "equational" - in meiosis I, it is “reductional” because the chromosome number is reduced from diploid to haploid - meiosis II is “equational” because the number of DNA in a cell is reduced but the chro- mosome number is not 2. Changes in C and n during meiosis - in meiosis I the n is halved and so is C - in meiosis II the n stays the same but the C is halved again 3. Mechanism of recombination during prophase - in meiosis I prophase, homologous chromosomes pair up - their sequences are very similar because they are homologous - recombination enzymes make cuts on the backbone of the homologous chromosomes and pastes them on another chromosome - cuts and pastes from non-sister chromatids - this is really kinda like a mutation - the switch is very precise, the same base pairs are cut and pastes - so it doesn’t really create problems - usually no bases are lost or gains - sexual recombination occurs all the time for males - because it happens in prophase of meiosis - females experience prophase of meiosis as a fetus, it gets past prophase and recombination and stops - known as mitotic arrest - they’ve already done sexual recombination but meiosis has not com- pletely finished - meiosis will finish when eggs are fertilized 4. Role of cohesin and synaptonemal complex - cohesin is a protein that holds sister chromatids together - it is essential for the assembly of the synaptonemal complex - as well as it holds the sister chromatids together, it is essential for the comple- tion of recombination and pairing of the (homologous chromosomes) ? - also ensures that the sister chromatids will each attach to a different spindle and therefore go to a different side Lecture 10 Lecture Outcomes - synaptonemal complex is a protein structure that forms between homologous chromo- somes during meiosis - it functions primarily as a scaffold to allow interacting chromatids to complete their crossover activities 5. How homolgues pair in order for all non-sister chromatids to participate in recombina- tion - homologous pairs on top of each other, so that each sister chromatid pairs with the non-sister chromatid - not side by side 6. mechanism by which recombination creates new combinations of alleles - bec
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