CBSE · Class 10 · Science · HeredityDiscuss the mechanism of sex determination in human beings. How is the sex of a child genetically determined at the time of fertilization? Support your answer with a suitable cross diagram explanation.

Introduction to Sex Determination\nSex determination is the biological system that determines the development of sexual characteristics in an organism. In human beings, sex determination is completely genetic and depends entirely on the type of sex chromosomes inherited from the parents.

Chromosomal Makeup in Humans

• Human cells contain 23 pairs of chromosomes (46 total chromosomes).
• Out of these, 22 pairs are autosomes, which determine general body characteristics and are identical in males and females.
• The 23rd pair consists of sex chromosomes, which differ in males and females:
  • Females possess two identical sex chromosomes designated as XX.
  • Males possess two different sex chromosomes designated as XY.

Role of Gametes

• Female Gametes (Ova): Since females are XX, all the eggs produced by a human female contain an X chromosome. Thus, females are homogametic.
• Male Gametes (Sperm): Since males are XY, half of the sperms produced contain an X chromosome and the other half contain a Y chromosome. Thus, males are heterogametic.

Genetic Cross at Fertilization\nSex is determined at the precise moment of fertilization, depending on which sperm fertilizes the egg:

1. Case 1 (Female Child): If a sperm carrying an X chromosome fertilizes an egg carrying an X chromosome, the resulting zygote has the XX combination, developing into a female child.
2. Case 2 (Male Child): If a sperm carrying a Y chromosome fertilizes an egg carrying an X chromosome, the resulting zygote has the XY combination, developing into a male child.

Conclusion and Societal Implication\nTherefore, it is scientifically evident that the father's sperm (carrying either X or Y chromosome) determines the sex of the child, and mothers have no role in determining the sex of the baby. This helps eliminate societal superstitions blaming women for bearing girl children.