Which statement about sex-linked traits is most accurate?

• A. It is always inherited from father to son
• B. It is carried on autosomes
• C. It is produced by mitochondrial DNA
• D. It is often more common in males due to X-linked inheritance

Answer: (D)

Sex-linked traits are determined by genes on the sex chromosomes, most often on the X chromosome. Males have one X and one Y, while females have two X chromosomes. For many X-linked traits, especially recessive ones, a male needs only one copy of the allele on his single X to express the trait, because there isn’t a second X to mask it. A female would need two copies of the same recessive allele to show the trait, so it appears less frequently in females. This is why such traits are often more common in males. An example is color vision deficiency, which is X-linked recessive. In contrast, autosomal traits don’t show this male bias, and traits involving mitochondrial DNA are inherited from the mother, not via the X chromosome.