Introduction to Genetic Analysis 80

Introduction to Genetic Analysis 80 - 44200_03_p73-114...

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79 3.1 Historical development of the chromosome theory Evidence from abnormal chromosome segregation The critical analysis that firmly established the chromo- some theory of heredity came from one of Morgan’s stu- dents, Calvin Bridges. He was able to predict that, if genes are located on chromosomes, certain unusual and unexpected genetic results should be explained by the occurrence of abnormal chromosome arrangements. He subsequently observed the abnormal chromosomes un- der the microscope, exactly as he had predicted. Bridges’s work began with a fruit fly cross that we have considered before: White-eyed females ± red-eyed males We can write the parental genotypes by using the conventional symbolism as X w X w (white-eyed) ± ± X w ² Y (red-eyed) ² .We have learned that the expected progeny are X w ² X w (red-eyed females) and X w Y (white- eyed males). However, when Bridges made the cross on a large scale, he observed a few exceptions among the large number of progeny. About 1 of every 2000 F 1 progeny was a white-eyed female or a red-eyed male. Collectively, these individuals were called
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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