MP Board · Class 10 · Science · Heredity and EvolutionWhat is sex determination? Explain the mechanism of sex determination in human beings with a neat schematic representation.

Definition of Sex Determination\nSex determination is a biological system that determines the development of sexual characteristics in an organism. It dictates whether an individual will develop male or female reproductive organs and associated traits. In many organisms, including humans, sex is determined genetically by specific chromosomes known as sex chromosomes.

Sex Determination Mechanism in Humans\nIn human beings, the chromosomal mechanism of sex determination is of the XX-XY type.

• Total Chromosomes: Every normal human somatic cell contains 23 pairs of chromosomes (46 total). Out of these, 22 pairs are autosomes, which determine general body characteristics, and 1 pair (2 chromosomes) constitutes the sex chromosomes.
• Female Genotype: Human females possess two identical sex chromosomes represented as XX. Therefore, all female gametes (ova) produced carry an X chromosome ($22 + X$).
• Male Genotype: Human males possess two different sex chromosomes represented as XY. Therefore, male gametes (sperm) are of two types: 50% carry an X chromosome ($22 + X$) and 50% carry a Y chromosome ($22 + Y$).

Schematic Representation of Fertilization\nWhen fertilization takes place:

1. If a sperm carrying an X chromosome fertilizes an ovum (X), the resulting zygote will have XX chromosomes, developing into a female child.
2. If a sperm carrying a Y chromosome fertilizes an ovum (X), the resulting zygote will have XY chromosomes, developing into a male child. \nThus, the statistical probability of having a male or female child is always 50:50, and it is scientifically evident that the father's sperm determines the sex of the child.