Another cross in Drosophila involved the recessive, X-linked genes yellow (y), w

Question

Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white- eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The Fi females were wild type for all three traits, while the Fi males expressed the yellow-body and white-eye traits. The cross was carried to an F2 progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was con- structed. Male Offspring ct 90 95 424 376 0 y Wct ct +wct (a) Diagram the genotypes of the Fi parents. (b) Construct a map, assuming that white is at locus 1.5 on the X chromosome. (c) Were any double-crossover offspring expected? (d) Could the F2 female offspring be used to construct the map? Why or why not?

Explanation / Answer

(A) F1 male Parent: yellow-body, white-eye which are recessive so the genotype should be y/y w/w Ct/+

Females are wild tpe: +/+ +/+ +/+

(c) Yes, the first two classes wth male offsprings 9 and 6 are with the double crossover

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