Practice question

X-linked recessive alleles reside physically on X chromosome. Males are hemizygous with XY constitution, possessing single X copy, so any recessive allele on that X fully expresses without masking. Females possess two X chromosomes, requiring two copies to show affected phenotype, usually remaining shielded as heterozygous carriers with normal phenotype. Therefore trait appears predominantly in males across pedigree, while females serve as transmitters. This explains male bias in hemophilia, Duchenne muscular dystrophy, and red-green color blindness pedigrees where affected males connect through unaffected carrier females.