Males have XY chromosomes, and females have XX chromosomes. X-linked recessive traits (such as red-green color blindness) appear when a defective X chromosome is not paired with a healthy X. Represent the defective X chromosome with lowercase x, so a child with xY or Yx will express the trait. A child with XX, XY, YX, xX, or Xx will not express the trait. Each parent passes one of their chromosomes to the child. What is the probability that a son will exhibit the trait if the mother has one faulty X chromosome and the father has normal XY chromosomes?
