Practice question

Father transmits Y chromosome to sons and X chromosome to daughters during fertilization. Since X-linked genes reside on X chromosome, father cannot transmit X-linked allele to son who receives paternal Y instead of paternal X. Sons obtain their single X exclusively from mother. Consequently father-to-son transmission in pedigree excludes X-linked inheritance and suggests autosomal or Y-linked pattern. In X-linked recessive pedigrees, affected males must receive mutant X from carrier mother, and affected fathers pass mutant X to all daughters, making them obligate carriers, never to sons.