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Unformatted text preview: Bio D137 Human and Eukaryotic Genetics Problem Set #3 J. L. Marsh Fall 2009 Due 10/13/09 1 Sex det & disjunction 1. Green-shifted colorblindness is sex-linked recessive. A green-shifted colorblind woman and a man with normal vision have a colorblind son with Klinefelter's syndrome. (a) Does the son's vision phenotype tell us whether nondisjunction occurred in the father or in the mother? Diagram two different cases of meiosis in the egg and sperm and the union of the necessary gametes that could produce a colorblind Klinefelter's from this union. Be sure to label the appropriate chromosomes with the alleles for color vision. Answer: For the son to be colorblind, he must inherit both X c s from the mother since this is recessive and a Y from the dad, so he is X c X c Y. So nondisjunction must have occurred during meiosis I OR meiosis II in the mother so that an X c X c egg is fertilized by a Y-bearing sperm (needed to mention the two types of meiotic ND and to show a diagram with the appropriate chromosomes labeled with the alleles for color vision to not lose points). (b) Repeat the above meiotic diagrams for the couple's next child who is a colorblind daughter with Turner syndrome. Answer: This daughter is X c O. Nondisjunction must have occurred in the father during meiosis I OR meiosis II so that a sperm without any sex chromosome fertilizes an egg with an X c chromosome (again, needed to mention the two types of meiotic ND and to show a diagram with the appropriate chromosomes labeled with the alleles for color vision to not lose points)....
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- Fall '09