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Unformatted text preview: 78 Chapter 3 The Chromosomal Basis of Inheritance In this context, Morgan constructed an interpreta- tion of his genetic data. First, it appeared that the X and Y chromosomes determine the sex of the fly. Drosophila females have four chromosome pairs, whereas males have three matching pairs plus a heteromorphic pair. Thus, meiosis in the female produces eggs that each bear one X chromosome. Although the X and Y chromo- somes in males are heteromorphic, they seem to pair and segregate like homologs, as we saw in Chapter 2. Thus, meiosis in the male produces two types of sperm, one type bearing an X chromosome and the other bear- ing a Y chromosome. Morgan then turned to the problem of eye color. He postulated that the alleles for red or white eye color are present on the X chromosome but that there is no counterpart for this gene on the Y chromosome. Thus, females would have two alleles for this gene, whereas males would have only one. The genetic re- sults were completely consistent with the known mei-...
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- Spring '08