Which chromosome pair determines biological sex in humans?

The 23rd pair of chromosomes in humans is responsible for determining biological sex. Humans have 46 chromosomes arranged in 23 pairs, with one chromosome inherited from each parent for each pair.

In the 23rd pair, there are two types of sex chromosomes: X and Y. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome is what specifically leads to male characteristics, while the absence of it (having two X chromosomes) results in female characteristics. Thus, this 23rd pair directly influences the development of the sexual traits and reproductive systems in humans, making it pivotal in determining biological sex.