Introduction to Genetic Analysis 81

Introduction to Genetic Analysis 81 - 80 Chapter 3 The...

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Unformatted text preview: 80 Chapter 3 The Chromosomal Basis of Inheritance To follow Bridgess logic, recall that in Drosophila XXY is a female and XO is a male. Bridges assumed that XXX and YO zygotes die before development is complete, so the two types of viable exceptional prog- eny are expected to be X w X w Y (white-eyed female) and X w O (red-eyed sterile male). What about the sterility of the primary exceptional males? This sterility makes sense if we assume that a male must have a Y chromo- some to be fertile. To summarize, Bridges explained the primary excep- tional progeny by postulating rare abnormal meioses that gave rise to viable XXY females and XO males. To test this model, he examined microscopically the chro- mosomes of the primary exceptional progeny, and in- deed they were of the type that he had predicted, XXY and XO. Therefore, by assuming that the eye-color gene was located on the chromosomes, Bridges was able to ac- curately predict several unusual chromosome rearrange- ments as well as a previously unknown genetic process, nondisjunction....
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