How does sex determination relate to chromosomes?

Sex determination is related to chromosomes as it is the specific combination of sex chromosomes that determines an individual's sex.

In humans and many other species, sex is determined by specific chromosomes known as sex chromosomes. These are different from the other chromosomes, known as autosomes, which are the same in both males and females. In humans, there are two types of sex chromosomes, X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

During sexual reproduction, each parent contributes one sex chromosome to the offspring. The mother, being XX, can only contribute an X chromosome. However, the father, being XY, can contribute either an X or a Y chromosome. If the father contributes an X chromosome, the offspring will be female (XX). If the father contributes a Y chromosome, the offspring will be male (XY). This is why it is often said that the father determines the sex of the child.

This system of sex determination is known as the XY system. However, it's worth noting that not all species use this system. Some species, such as birds, use a ZW system where the female determines the sex of the offspring. In these species, males are ZZ and females are ZW.

In addition to determining sex, sex chromosomes also carry genes that control the development of sexual characteristics. For example, the Y chromosome in humans carries the SRY gene, which triggers the development of male characteristics. If this gene is missing or non-functional, the individual will develop as a female despite having a Y chromosome. This shows that sex determination is not just about the presence or absence of certain chromosomes, but also about the specific genes they carry.