Sex-linked

A sex-linked trait results from a gene located on a sex chromosome (in humans, either the X or Y chromosome). In practice, most often "sex-linked" refers to X-linked traits, since the X chromosome carries many more genes than the Y. These traits show different patterns of inheritance in males and females due to their linkage to the sex chromosomes.

• Sex-linked is an umbrella term covering both X-linked and Y-linked inheritance. However, because X-linked traits (like hemophilia or color blindness) are far more common, "sex-linked" is often used synonymously with X-linked in many contexts.
• Sex-linked traits differ from autosomal traits in that an individual's sex influences expression. For example, an X-linked recessive trait might affect primarily males (since males have only one X), whereas females can be carriers. Always consider the sex distribution in a pedigree when determining if a trait is sex-linked.
• If you see the term "sex-linked" in study materials or exam questions, make sure to apply the rules of X-linked inheritance (no father-son transmission, possible carrier females, etc.) unless the question explicitly specifies Y-linked. It usually implies that the gene in question lies on the X chromosome.

• Questions might directly use the phrase "sex-linked inheritance" - typically, they expect you to recognize an X-linked pattern. For instance, a problem may describe a trait that appears mostly in males and is passed through female carriers; identifying it as a sex-linked (X-linked) trait is key.
• In pedigree problems, a sex-linked trait will show characteristic clues: it may skip generations via female carriers and rarely (or differently) affect one sex. If a trait is described as sex-linked without further detail, assume X-linked and look for the telltale signs (e.g., more males affected, no male-to-male transmission).