Which of the following is NOT a characteristic of X-linked recessive inheritance?

In X-linked recessive inheritance, affected individuals are typically male, as they have only one X chromosome. Males inherit their single X chromosome from their mother while receiving a Y chromosome from their father. This means that if a male has the mutant allele on his X chromosome, he will express the trait because there is no corresponding allele on the Y chromosome to mask it.

D states that all affected individuals have two copies of the mutant allele, which is not accurate in the context of X-linked recessive conditions. Affected males only have one copy of the mutant allele, whereas females would need two copies to be affected, as females have two X chromosomes. Therefore, the correct answer indicates a misunderstanding of the inheritance pattern—only females would have to have two copies of the mutant allele to express the trait, whereas males express it with just one.

The other statements reflect true aspects of X-linked recessive inheritance. For instance, females can be carriers if they have one copy of the mutant allele, but this does not make them affected. The pattern of inheritance primarily affecting males, along with the absence of male-to-male transmission, aligns with the established principles of X-linked recessive inheritance.