CBSE · Class 10 · Science · HeredityWhat is sex determination? Explain the mechanism of sex determination in human beings with the help of a flow chart or description. How does it differ from environmental sex determination in some animals?

Introduction to Sex Determination\nSex determination is the biological system that determines the development of sexual characteristics in an organism. Most sexually reproducing organisms have two sexes. The genetic mechanism of sex determination dictates whether an individual develops male or female reproductive organs.

Mechanism of Sex Determination in Humans\nIn human beings, sex determination is genetically controlled and depends on the type of sex chromosomes inherited from the parents.

• Total Chromosomes: Humans have 23 pairs of chromosomes (46 total), out of which 22 pairs are autosomes and 1 pair (2 chromosomes) are sex chromosomes.
• Female Chromosomes: Females have two identical sex chromosomes represented as XX.
• Male Chromosomes: Males have one X and one smaller Y chromosome, represented as XY.

Gamete Formation and Fertilization

• Sperm (Male): Half of the sperms carry the X chromosome, and the other half carry the Y chromosome.
• Ova (Female): All eggs produced by the female carry only the X chromosome.

Determination Process

• If a sperm carrying an X chromosome fertilizes an egg (X), the resulting zygote will have XX chromosomes and develop into a female.
• If a sperm carrying a Y chromosome fertilizes an egg (X), the resulting zygote will have XY chromosomes and develop into a male.\nThus, the male gamete (sperm) plays the deciding role in determining the sex of the child.

Comparison with Environmental Sex Determination\nUnlike humans where sex is genetically determined by chromosomes, in some animals (e.g., reptiles like turtles and lizards), the environmental temperature at which fertilized eggs are incubated determines the sex of the offspring. For instance, high temperatures may lead to the development of females in certain turtles, whereas in some snails, individuals can change sex during their lifetime based on social cues or environment.