Question

Summarize 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 the idea that mutations causing male lethality are X‑linked. Only about half of the F1 females produce the predicted deficit of male offspring, consistent with those females being heterozygous (one normal X and one mutant X), while surviving males carry only the normal X (males inherit their single X from their mothers, so a mutated maternal X can cause male lethality and skew the sex ratio). Classic experiments by Muller—inducing mutations on the male X with radiation and following them through crosses—further showed that the X chromosome can acquire and transmit such mutations. The authors note the hypothesis would be updated if unexpected data reveal additional mutations or patterns.