Sex determination means that a newborn would be a male baby like father or female baby like the mother. The mechanism of sex determination in humans is controlled by genetic factors, specifically the sex chromosomes. Humans have two types of sex chromosomes: X and Y. The combination of these chromosomes inherited from the parents determines the biological sex of the individual.
6.4.1 Chromosomal Basis of Sex Determination
Humans have 46 chromosomes in total, arranged in 23 homologous pairs. Each homologous pair consists of two structurally similar but functionally different chromosomes. One of which is maternal that comes from the mother and the other is paternal that comes from father. Out of these 23 pairs, 22 pairs are autosomes, which are the same in both males and females, and 1 pair is sex chromosome pair, which is different in male and female individuals. As show in the human karyotype in figure 6.10. In females, the sex chromosome pair consists of two completely homologous chromosomes called XX. In males, the sex chromosome pair consists of two partially homologous chromosomes called X and Y.
6.4.2 Role of Sperm and Egg
During reproduction, each parent contributes one sex chromosome to the offspring. The mother can only contribute an X chromosome, as she is XX, therefore, during oogenesis every time the egg would take either of the X chromosome. Since mother can produce only same type of gametes, therefore, the human female is called homogametic sex.