The coagulation factors with a sex-linked recessive inheritance pattern are which pair?

• A. Factor V and Factor VIII
• B. Factor VIII and Factor IX
• C. Factor IX and Factor X
• D. von Willebrand factor and Factor VIII

Answer: (B)

Factor VIII and Factor IX are the coagulation factors whose genes sit on the X chromosome, so their deficiencies exhibit an X-linked recessive inheritance pattern. In this pattern, males are affected when they inherit the mutated X, while females are typically carriers unless there is another contributing factor. An affected male passes the mutated X to all daughters (making them carriers) and passes a Y to sons (who are usually unaffected). A carrier female has a 50% chance with each pregnancy to pass the mutated X to offspring, resulting in affected sons and carrier daughters.

The other options involve genes on autosomes or factors not linked to the X chromosome (Factor V and Factor X are autosomal; von Willebrand factor is autosomal), so they do not show X-linked recessive inheritance.