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Lec 10 Meiosis.docx

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Biology 1001A

Lecture 10: Meiosis Products of meiosis in animals vs. plants, fungi, algae - After meiosis I, cells are already haploid (contain one chromosome from each homologous pair) - Produces of meiosis in animals are haploid gametes - In plants, gametes are formed from mitotic division of specific sporophyte tissues Timing of meiosis in vertebrate life cycles (humans) - Spermatogenesis: cell produces 4 equal-sized sperm o Testes have millions of cells continuously producing sperm through meiosis - Oogenesis: cytokinesis divides cytoplasm unevenly o Only one daughter cell will have a large volume o Others will are minimal and non-functional (cannot develop into viable offspring) Main differences between meiosis and mitosis Mitosis Meiosis Produces genetically identical offspring Produces daughter cells that are genetically distinct from, and contain half as much DNA as, their parent cells Somatic cells Gametes One cell division (2 daughter cells) Two cell division (4 daughter cells) Produces cells with 2x as many Produces cells with half as many chromosomes as mitosis chromosomes as meiosis Characteristics of homologous chromosomes - Same genes but possibly different alleles (DNA sequence) than homologous partner o Homozygous for a gene when both have same allele o Heterozygous for a gene when chromosomes have differing alleles - Same size and shape - Toward beginning of meiosis I, homologous chromosomes move together and are held together by protein complex called the synaptonemal complex Meiosis I is “reductional” because cell is going from diploid to haploid - Meiosis II is “equational” because the daughter cells stay haploid Changes in C and n during meiosis Mechanism of recombination during prophase - Recombination during meiosis is what causes CNVs - Double stranded change in the sequence of the chromosome - Sexual recombination happens in meiosis I o Homologues do not pair side-by-side; they overlap! - Women: recombination is done before they are done (as fetus) and cells sit in meiotic
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