1. Sex Chromosomes: Humans have 23 pairs of chromosomes, out of which one pair determines the sex of an individual. These are called sex chromosomes, labeled as X and Y.
- Females (XX): Females typically have two copies of the X chromosome (XX).
- Males (XY): Males have one X chromosome and one Y chromosome (XY).
2. The SRY Gene: The sex-determining gene, known as the SRY (Sex-determining Region Y) gene, is located on the short arm of the Y chromosome. It plays a crucial role in initiating the development of male characteristics.
- When a sperm cell carrying the Y chromosome fertilizes an egg (containing an X chromosome), it introduces the SRY gene into the developing embryo.
- The SRY gene triggers the differentiation of the gonads into testes instead of ovaries. Testes produce male hormones, including testosterone, which lead to the development of male reproductive organs and male physical traits.
3. Sperm Determination: During sperm production (spermatogenesis), some cells in the testes undergo genetic recombination, which involves the exchange of genetic material between chromosomes. This process can result in the creation of sperm cells that carry either the X chromosome or the Y chromosome.
- If the sperm carries the X chromosome, it can combine with the X chromosome in the egg, resulting in a female (XX) embryo.
- If the sperm carries the Y chromosome (with the SRY gene), it can combine with the X chromosome in the egg, leading to a male (XY) embryo.
Therefore, it is the presence or absence of the SRY gene on the Y chromosome inherited from the father that ultimately determines whether the offspring will be a boy (XY) or a girl (XX).
