Question

Men have XY​ (or YX) chromosomes and women have XX chromosomes.​ X-linked recessive genetic diseases​ (such as juvenile​ retinoschisis) occur when there is a defective X chromosome that occurs without a paired X chromosome that is not defective. Represent a defective X chromosome with lowercase​ x, so a child with the xY or Yx pair of chromosomes will have the disease and a child with XX or XY or YX or xX or Xx will not have the disease. Each parent contributes one of the chromosomes to the child. Complete parts a through d below. a. If a father has the defective x chromosome and the mother has good XX​ chromosomes, what is the probability that a son will inherit the​ disease? 0.333

Answer 1

The probability that a son will inherit the​ disease is zero.

The human males are XY and females are XX. In addition, fathers pass their Y chromosome to their sons and X chromosome to their daughters. In contrast, mother pass one X to chromosome to son and another X chromosome to daughters.

In the given scenario, father is xY and mother is XX. Thus, father will pass x to daughters to Y to sons. The mother pass one X chromosome to son as well as daughters.

Thus, the genotype of the sons will be XY and that of daughters will be Xx. Hence, all the daughters will be carrier and all the sons will be unaffected.

The same is explained in the Punnette square in the figure below.