In X-linked recessive inheritance, which statement is true?

In X-linked recessive inheritance, which statement is true?

• A. It is always lethal in males.
• B. It is carried by females and predominantly affects males.
• C. It affects males and females equally.
• D. It is carried by males and predominantly affects females.

Answer: (B)

In X-linked recessive traits, the gene is on the X chromosome. Males have one X and one Y, so a single mutated allele on their X will express the condition. Females have two X chromosomes, so a single mutated allele usually doesn’t express because the normal copy on the other X masks it; they are typically carriers. This pattern means the condition is carried by females and predominantly affects males. If a carrier mother and an unaffected father have children, about half the sons may be affected, while daughters may be carriers; an affected father can pass the mutation to all daughters (making them carriers), but not to sons.

In X-linked recessive traits, the gene is on the X chromosome. Males have one X and one Y, so a single mutated allele on their X will express the condition. Females have two X chromosomes, so a single mutated allele usually doesn’t express because the normal copy on the other X masks it; they are typically carriers. This pattern means the condition is carried by females and predominantly affects males. If a carrier mother and an unaffected father have children, about half the sons may be affected, while daughters may be carriers; an affected father can pass the mutation to all daughters (making them carriers), but not to sons.