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Unformatted text preview: 124 Chapter 4 Eukaryote Chromosome Mapping by Recombination a b 3 1 4 1 4 1 4 1 4 Gametes P Meiotic diploid (F 1 ) (Tester) Parental type Parental type Recombinant Recombinant Testcross progeny A B a b a b A B a b A B A B a b a b A B a b a b a b A b a b a B a b 3 , , . . Figure 4-10 Frequencies of recombinants arising from crossing-over. The frequencies of such recombinants are less than 50 percent. 4.3 Linkage maps As Morgan studied more and more linked genes, he saw that the proportion of recombinant progeny varied con- siderably, depending on which linked genes were being studied, and he thought that such variation in recombi- nant frequency might somehow indicate the actual dis- tances separating genes on the chromosomes. Morgan as- signed the study of this problem to a student, Alfred Sturtevant, who (like Bridges) became a great geneticist. Morgan asked Sturtevant, still an undergraduate at the time, to make some sense of the data on crossing-over be- tween different linked genes. In one night, Sturtevant de- veloped a method for mapping genes that is still used to- day. In Sturtevants own words, In the latter part ofday....
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- Spring '08