Practice question

In Drosophila with XY sex determination, males possess single X chromosome and Y lacking most X genes. For locus on X, male genotype contains only one allele, genetic condition termed hemizygous, distinct from homozygous bearing two identical alleles or heterozygous bearing two different alleles. Hemizygous recessive allele expresses phenotype directly because no second allele masks it, explaining higher frequency of X-linked recessive traits in males. Transmission pattern shows father passes X to daughters only, Y to sons, shaping pedigree where affected males transmit trait to grandsons via carrier daughters rather than directly to sons.