Practice question

Hemophilia A and B result from loss-of-function mutations in F8 and F9 genes encoding coagulation factors VIII and IX, located on long arm of X chromosome at Xq28 and Xq27. Because males possess single X, hemizygous deficiency causes severe bleeding disorder, while heterozygous females are usually asymptomatic carriers due to random X-inactivation providing sufficient clotting factor from normal allele. Pedigrees show affected males connected through carrier females, classic example described historically in Queen Victoria family. Inheritance follows X-linked recessive pattern with characteristic absence of father-to-son transmission.