7 - BIO 320 Lecture 7 Chromosome aberrations Changes in...

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BIO 320: Lecture 7 Chromosome aberrations: Changes in number and structure CHANGES IN CHROMOSOME NUMBER: Euploid -- all sets of chromosomes are complete For an organism with n = 3, the diploid number is 2n = 6. Aneuploid -- a set of chromosomes is incomplete; often arises from chromosome nondisjunction during meiosis. Some examples: Monosomic , a chromosome is missing in diploids In humans, X0 Turner syndrome females are monsomic for the X chromosome. Trisomic , three copies of a chromosome are present in a diploid (2n +1) or a haploid (n +2) In humans, Down syndrome is caused by trisomy 21. Polyploids having an odd number of chromosome sets tend to be infertile. In triploids, for example, the third homolog segregates randomly so half of the gametes are disomic for any given chromosome: Meiosis I Meiosis II n +1 (disomic) n + 1 n n (disomic) (2n-1) Chapter 14: 14-1, 14-4a-d, 14-8, 14-10, 14-11, 14-13, 14-14, 14-17,14-29, 14-30, 14-31, 14-38; QB I1-27 2008
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7 - BIO 320 Lecture 7 Chromosome aberrations Changes in...

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