Question

To determine whether radiation associated with the atomic bombings of Hiroshima and Nagasaki produced recessive germ-line mutations, scientists examined the sex ratio of the children of the survivors of the blasts. Can you explain why an increase in germ-line mutations might be expected to alter the sex ratio?

Answer 1

Recessive germ-line mutations on the X chromosome have the potential to alter the sex ratios. Female offspring who have a single recessive mutation on the X chromosome will also possess a nonmutated allele on their other X chromosome. Therefore, females will be heterozygous for the pair of alleles. Male offspring, however, have only one X chromosome, and a mutation within an allele on the X chromosome will result in a phenotypic change. If the allele mutated is essential, then the mutation for males will be lethal. Essentially, recessive mutations on the X chromosome in the germ-line could lead to fewer males being born.