What type of chromosomes are responsible for determining the sex of a person?

The presence of the X and Y chromosomes plays a critical role in determining an individual's biological sex. Humans typically have two sex chromosomes that come in pairs: one X chromosome and one Y chromosome for males (XY), and two X chromosomes for females (XX).

The Y chromosome carries specific genes that are essential for the development of male characteristics, while the X chromosome contains a variety of genes that are involved in numerous biological processes. When an egg, which always carries an X chromosome, is fertilized by sperm that carries either an X or a Y chromosome, the sex of the offspring is determined. If the sperm delivers an X chromosome, the resulting genotype will be XX, leading to female development. If the sperm delivers a Y chromosome, the offspring has the XY genotype, resulting in male development.

Thus, the combination of both the X and Y chromosomes is what ultimately determines a person's sex, making the pair responsible for this vital aspect of human genetics.