CBSE · Class 10 · Science · HeredityHow is sex determined in human beings? Explain the genetic mechanism involved.

Sex determination in human beings is a genetic process controlled by sex chromosomes. Humans possess 23 pairs of chromosomes, out of which 22 pairs are autosomes and 1 pair consists of sex chromosomes. Females have two identical sex chromosomes designated as XX, while males have one X chromosome and one smaller Y chromosome designated as XY. Because females produce only one type of egg cell containing an X chromosome, they are homogametic. In contrast, males produce two different types of sperm cells in equal proportions: 50% of the sperms carry an X chromosome, and the other 50% carry a Y chromosome; thus, males are heterogametic. The sex of the child is entirely determined by which type of sperm fertilizes the egg. If a sperm carrying an X chromosome fertilizes the egg (X), the resulting zygote will have XX chromosomes, developing into a female child. If a sperm carrying a Y chromosome fertilizes the egg (X), the zygote will have XY chromosomes, developing into a male child. Therefore, the father's contribution of genetic material determines the gender of the offspring.