Suppose you are carrying out a series of crosses with an insect where the mechanism of sex determination is unknown.You discover a mutant female with short bristles and decide to cross it with a wild type male that has normal bristles.Half of the F₁ progeny have short bristles but all of these short-bristled F₁ progeny are males.Based on these results,a valid hypothesis would be A)Males are ZW,females are ZZ,and short bristles are caused by a dominant allele on the Z chromosome. B)Males are ZZ,females are ZW,and short bristles are caused by a recessive allele on the Z chromosome. C)Males are ZZ,females are ZW,and short bristles are caused by a dominant allele on the W chromosome. D)Males are ZZ,females are ZW,and short bristles are caused by a dominant allele on the Z chromosome.

Question

Quizplus · Accepted Answer

If the mutant female with short bristles is carrying a dominant allele on one of her sex chromosomes (Z or W), then when mated to a wild type male, all of her male offspring (who inherit her single X chromosome along with either a Z or a W) will exhibit the mutant phenotype. This is consistent with the observed results. Since all short-bristled progeny were male, this suggests that the mutant allele is on the Z chromosome (which males inherit only from their mother in this system). The fact that half of the progeny had short bristles indicates that the mutant female was heterozygous for the trait. Therefore, a valid hypothesis is that males are ZZ, females are ZW (consistent with what is known about insect sex determination), and short bristles are caused by a dominant allele on the Z chromosome.

Suppose You Are Carrying Out a Series of Crosses with an Insect