Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Humans have 46 chromosomes thus they have 23 pairs of chromosomes. Of these 23 pairs 22 pairs are autosomes and the remaining 1 pair is the sex chromosome that determines the sex of the child. In humans sex chromosome is of two types X and Y. The genetic composition of females is 44+XX whereas males have a genetic composition of 44+XY. As humans are diploid organisms and during fertilization the child receives half of its chromosomes from one parent and the other half from another the diploid state is restored. Now, the gametes formed by the female is all 22+X where as males produce two types of gametes, 22+X and 22+Y. During fertilization if the female gamete with 22+X chromosome is fertilized by the sperm bearing 22+X chromosome the resulting zygote has the genetic composition as 44+XX thus giving rise to a female child. But, if the female gamete with 22+X chromosome is fertilized by the sperm bearing 22+Y chromosome the resulting zygote has the genetic composition as 44+XY thus giving rise to a male child. Thus the sex of the child is determined by the type of sperm that fertilizes the ovum and not the other way round.