Inheritance160-page9

Inheritance160-page9 - While the ratio of 3:1 was obtained...

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Inheritance Patterns - 9 Some species have the reverse pattern of sex chromosomes (male = XX and female = XY), and some species have one gender (female) with a pair of chromosomes and one gender (male) with a single unmatched chromosome. In all cases the gender with the dissimilar pattern will determine the gender of the offspring. Sex Linkage In 1910, Thomas Hunt Morgan, who spent much of his career studying inheritance patterns of the fruit fly, Drosophila melanogaster , discovered the presence of a white eye in certain individuals. Since this was a distinctive feature, Morgan decided to study the inheritance pattern for this recessive eye color. Morgan made several crosses using a white-eyed male, expecting the standard Mendelian results. He did not get them.
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Unformatted text preview: While the ratio of 3:1 was obtained, all of the white-eyed second generation offspring were male flies. All females had red eyes (and 25% of the males also had red eyes). Morgan did a series of reciprocal crosses of white-eye males with red-eye females and red-eye males with white-eye females. He concluded that the gene for eye color in the fruit fly was located on the X chromosome. Males passed the trait to their daughters (on their solitary X chromosome) and mothers passed the trait to sons. White eyed females could also pass the white eye allele to their daughters, but if the father fly had red eyes, the eye color of the daughters would be red, while the eye color of the sons of white-eyed females would always be white....
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