What is the purpose of sex chromosomes?

The purpose of sex chromosomes is primarily to determine the sex of an individual. In many organisms, such as humans, there are two types of sex chromosomes: X and Y. The presence of two X chromosomes typically results in a female phenotype, while an X and a Y chromosome combination typically results in a male phenotype. This genetic distinction is crucial for sexual reproduction, influencing not just the biological sex but also sexual development and associated traits.

Sex chromosomes carry genes that are involved in sex differentiation and reproductive functions. For instance, the SRY gene located on the Y chromosome is critical for driving male development. Thus, the correct answer highlights the essential role these chromosomes play in establishing and regulating biological sex, a fundamental aspect of genetics that has significant implications for an organism's development and reproduction.