Question

Shorten The new X chromosome data supports the hypothesis that mutations causing male lethality are X-linked, as evidenced by the inheritance patterns in the offspring of crossed D. melanogaster flies. This is supported by observations that only half of the F1 females produce fewer male offspring as predicted, indicating that these females carry one normal X and one mutant X, while all living males carry only the normal X chromosome. The observation that females with a mutant X chromosome produce fewer males is also consistent with the understanding that males inherit their single X chromosome from their mothers. If the X chromosome is mutated, it can lead to lethality, thereby affecting the ratio of the offspring. Further evidence for X-linked genes comes from the famous experiments by Muller, who demonstrated that inducing mutation through radiation on the male Drosophila's X-chromosome could produce a variety of mutations when these males were crossed with females. The resulting F1 generation, when crossed again, produced offsprings from which the mutated genes could be studied, confirming that radiation could alter the genetic material on the X chromosome. In the event of unexpected data, the hypothesis would be revised to include new possible mutations.

Answer 1

New X-chromosome data support that male-lethal mutations are X-linked. Only half the F1 females produce fewer male offspring, consistent with heterozygous females (one normal, one mutant X) while surviving males carry only the normal X; because males inherit their single X from their mothers, a mutant maternal X causes male lethality and skews sex ratios. Muller's radiation experiments—inducing mutations on the X in males and following the F1 and later crosses—further confirmed heritable X-linked mutations. Unexpected data would prompt revising the hypothesis to include additional mutations.