Final answer:
Option (b), The claim that an X-linked recessive trait never appears in females and affects only 1/4 of sons of a carrier female is false. The correct probability for a son of a carrier mother to be affected by an X-linked recessive trait is 50 percent.
Step-by-step explanation:
The statement that an X-linked recessive trait is never seen in females and affects 1/4 of all the sons of a female carrier is false. Females can exhibit X-linked recessive traits if they inherit two copies of the recessive allele, one from each parent. For a son of a female carrier of an X-linked recessive disorder, there is actually a 50 percent chance of being affected, as males have only one X chromosome and the presence of the recessive allele on this chromosome will result in the expression of the trait.
Females can be carriers of an X-linked recessive trait if they inherit one recessive allele and one normal allele. In this case, they do not express the trait because they have a normal allele on their other X chromosome. When a female carrier has children, she can pass on the recessive allele to her daughters, making them carriers, or to her sons, who may express the trait. X-linked recessive disorders are more common in males because they only have one X chromosome and therefore express the trait when they inherit the recessive allele.