Lecture 4

Lecture 4 - BICD 100 Genetics Winter 2008 Andrew Chisholm...

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Lecture 4 17/1/08 Meiosis, chromosomes and sex Genes are on chromosomes. Behavior of chromosomes in meiosis underlies Mendelian genetics. Don’t confuse chromosomes vs chromatids vs chromatin. # chromosomes = # centromeres. # chromatids = # DNA molecules. chromatin = DNA + proteins (+ some RNA) What’s special about meiosis compared to mitosis? Pairing of homologs in prophase of Meiosis I. Crossing-over (recombination) between homologs. Pairing means that homologs disjoin in Meiosis I anaphase: Law of equal segregation. Number of chromosomes is reduced by half. Be familiar with the terms prophase, metaphase, anaphase, telophase. Meiosis II resembles mitosis--equational division-- except that no DNA replication, so number of DNA molecules is halved. Chromosomes segregate independently in Meiosis II: Law of Independent Assortment., How meiosis actually happens in animals Male and female germ lines generate spermatogonia and oogonia. 1° and 2° spermatocytes/ oocytes. Typically all four products of male meiosis become spermatozoa, but only one product of female meiosis becomes oocyte. In plants a more complex sequence of events but the genetic consequences are the same. The Chromosome Theory of Inheritance
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This note was uploaded on 05/31/2009 for the course BICD 100 taught by Professor Nehring during the Spring '08 term at UCSD.

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Lecture 4 - BICD 100 Genetics Winter 2008 Andrew Chisholm...

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