What is the role of a sex chromosome?

The role of a sex chromosome is primarily to define an individual's sex. In many organisms, including humans, sex chromosomes are designated as X and Y. The presence of specific combinations of these chromosomes—XX typically indicating female and XY typically indicating male—dictates the biological sex of the individual. This differentiation plays a crucial role in the development of sex-specific characteristics and reproductive anatomy.

While sex chromosomes can influence certain traits, their primary function is to establish sex, which is a critical aspect of reproduction and hereditary patterns. Therefore, the focus on sex determination makes it clear why the answer related to defining an individual's sex is accurate. In contrast, while the other options discuss important genetic functions, they pertain more to broader genetic roles rather than the specific function of sex chromosomes in determining sex.