Mapping Chromosomes Problem 2
A. In the fruit fly, scute (sc, missing bristles), crossveinless (cv, wing veins missing), and echinus (ec, rough eye) are all located on the X chromosome. A homozygous scute, crossveinless female fly was mated to an echinus male fly. Phenotypically wid type first generation offspring females heterozygous for these traits were mated to fully mutant males, and the following progeny were observed.
1. With respect to these three genes, what are the genotypes of the parents used in making the phenotypically wild first generation heterozygote?
2. Which gene is in the middle?
3. What are the map distances between the three genes?
4. Calculate the coefficient of coincidence and explain what it means.
B. In the fruit fly, three recessive X chromosome mutants are scute (sc), sable body (s), and vermillion eyes (v). Females heterozygous normal (wilds type) for all three of these traits were mated to males that were mutant for all three traits, and the following testcross femal progeny (1000 total) were observed.
1. With respect to the three genes mentioned in the problem, show the genotypes of the first generation females and the male tester parents used in developing the testcross progeny.
2. Which of the offspring are derived from double crossover female gametes?
3. Which gene is in the middle?
4. What are the map distances between each of the end genes and the middle gene?
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