Which statement is always true when describing sex-linked inheritance?

• A. All sex-linked traits are inherited from the father.
• B. Females cannot be carriers of X-linked recessive disorders.
• C. Y-linked traits are equally common in both sexes.
• D. Males are more likely than females to express recessive X-linked traits.

Answer: (D)

Verified step by step guidance

1. Understand the concept of sex-linked inheritance: Sex-linked traits are associated with genes located on the sex chromosomes (X and Y). Males have one X and one Y chromosome, while females have two X chromosomes.
2. Recognize the difference between X-linked and Y-linked traits: X-linked traits are carried on the X chromosome, while Y-linked traits are carried on the Y chromosome. Y-linked traits can only be passed from father to son, as only males have a Y chromosome.
3. Analyze why males are more likely to express recessive X-linked traits: Males have only one X chromosome, so if they inherit a recessive allele on the X chromosome, it will be expressed because there is no second X chromosome to provide a dominant allele to mask it.
4. Understand why females can be carriers of X-linked recessive disorders: Females have two X chromosomes, so they can inherit one recessive allele and one dominant allele. The dominant allele masks the recessive allele, making them carriers without expressing the disorder.
5. Evaluate the incorrect statements: 'All sex-linked traits are inherited from the father' is false because X-linked traits can be inherited from either parent. 'Females cannot be carriers of X-linked recessive disorders' is false because they can be carriers. 'Y-linked traits are equally common in both sexes' is false because Y-linked traits only affect males.