Sex chromosomes are a specific type of chromosome that determine the biological sex of an organism. In humans, there are two sex chromosomes: X and Y. Typically, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome usually triggers male development. These chromosomes carry genes that influence sexual characteristics and reproductive functions. For example, the SRY gene located on the Y chromosome is crucial for the development of male traits. In contrast, the absence of a Y chromosome leads to the development of female traits.