If a man has a recessive sexlinked disorder, he has a 0% chance of passing it onto his son. Why?

Question

William Albracht · Accepted Answer

See explanation.

Most sex-linked traits are on the X sex chromosomes. Females have two X sex chromosomes and males have one X and one Y sex chromosomes. A female inherits an X chromosome from each parent. A male inherits an X chromosome exclusively from his mother and a Y chromosome exclusively from his father.

A man with an X-linked recessive disorder cannot pass on the disorder to a son because he exclusively passes on the unaffected Y chromosome to his son. The son's X chromosome comes exclusively from his mother.

The following image shows the inheritance of the X-linked recessive allele for hemophilia in which the father has the disorder and the mother is homozygous for normal blood clotting.

Maya Anderson · Answer

undefined A man with a recessive sex-linked disorder passes his Y chromosome to his son, which does not carry the gene for the disorder. Since the gene for the disorder is located on the X chromosome, his son receives the X chromosome from his mother, who would need to be a carrier or affected by the disorder for the son to inherit it. Therefore, the man has a 0% chance of passing the disorder to his son.