If a Man Expresses an X-Linked Recessive Trait,____

Question

If a man expresses an X-linked recessive trait,____.
A) all of his brothers will also express it
B) his father transmitted the trait to him
C) his father carried the trait
D) all of his sisters will also express it
E) his mother was heterozygous or homozygous for the trait

Accepted Answer

Since X-linked recessive traits are carried on the X chromosome, if a man expresses the trait, he must have inherited the mutated allele from his mother. Therefore, his mother must either be a carrier of the trait (heterozygous) or express the trait (homozygous). His father may or may not carry the trait, and his siblings may or may not express the trait depending on their own genetic makeup.