If a man expresses an X-linked recessive trait, we can draw the following conclusion:

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X-linked recessive traits are carried on the X chromosome. Since males only have one X chromosome, if they express an X-linked recessive trait, it means they inherited the mutated gene from their mother who is either heterozygous or homozygous for the trait. The father may have carried the mutation, but he did not transmit it to his son if he does not show the trait. Not all brothers will show the trait, as it depends on their mother's carrier status.

If a Man Expresses an X-Linked Recessive Trait, We Can