Principles of Inheritance and Variation

The pedigree fits X-linked recessive inheritance (affected $F_0$ mother → all daughters carriers; carrier mother → affected son). The $F_2$ cross is carrier female $X^A{X}^a$ × affected male $X^{a}Y$: offspring $X^A{X}^a$ (carrier daughter), $X^a{X}^a$ (affected daughter), $X^{A}Y$ (normal son), $X^{a}Y$ (affected son), each 1/4. Probability of a disease-free carrier is 1/4.