Mapping - MAPPING GENES A normal woman whose colorblind...

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MAPPING GENES A normal woman whose colorblind father had normal blood clotting has a son who has hemophilia. Could she have any normal sons? Is there a risk of having sons with both genetic defects? Since both of these genes are on the X chromosome, she must carry recessive alleles of the colorblindness and clotting factor genes on different X-chromosomes. That is her X chromosomes have the following gene composition with respect to these two traits: Cb h cb H If X chromosomes always segregate "intact" to opposite poles in meiosis I , every son would be either a hemophiliac or colorblind. As it turns out, however, new gene combinations can be created, by a process called crossing-over or recombination . Crossing-over occurs during prophase of meiosis I. It occurs after the already duplicated chromosomes have paired ( synapsis ). Most paired chromosomes will undergo at least one crossover Any one crossover involves only 2 of the 4 chromatids present. At most, 1/2 of the gametes will show "recombination"
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This note was uploaded on 04/29/2008 for the course GENE 310 taught by Professor Magill during the Spring '08 term at Texas A&M.

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Mapping - MAPPING GENES A normal woman whose colorblind...

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