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In Drosophila, a cross was made between females expressing the three X-linked recessive traits, scute bristles (sc), sable body (s), and vermilion eyes (v), and wild-type males. All females were wild type in the F1, while all males expressed all three mutant traits. The cross was carried to the F2 generation and 1000 offspring were counted, with the results shown in the following table. No determination of sex was made in the F2 data. (a) Using proper nomenclature, determine the genotypes of the P1 and F1 parents. (b) Determine the sequence of the three genes and the map distance between them. (c) Are there more or fewer double crossovers than expected? (d) Calculate the coefficient of coincidence; does this represent positive or negative interference?
Offspring | |||
SC | s | V | 314 |
+ | + | + | 280 |
+ | s | V | 150 |
sc | + | + | 156 |
sc | + | V | 46 |
+ | s | + | 30 |
sc | s | + | 10 |
+ | + | V | 14 |
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