Question

“In human beings, the sex of a newborn child depends on the father and not the mother.” Justify this statement with the help of a flow diagram.

Hint:

Only the father’s sperm determines the sex because the mother only contributes X chromosomes.

Answer 1

Humans have 23 pairs of chromosomes, out of which one pair are sex chromosomes: - Females have XX chromosomes. - Males have XY chromosomes. The mother always contributes an X chromosome through the egg. The father’s sperm may carry either an X or a Y chromosome: - If the sperm carrying an X chromosome fertilises the egg (X), the child will be XX (female). - If the sperm carrying a Y chromosome fertilises the egg (X), the child will be XY (male). \[ \text{Father (XY)} \xrightarrow{\text{produces}} \text{X-sperm or Y-sperm} \\ \text{Mother (XX)} \xrightarrow{\text{produces}} \text{only X-egg} \] Flow Diagram: \[ \begin{array}{c} \text{Sperm (X)} + \text{Egg (X)} \longrightarrow \text{XX (Girl)} \\ \text{Sperm (Y)} + \text{Egg (X)} \longrightarrow \text{XY (Boy)} \end{array} \] Therefore, the sex of the child depends on whether an X or Y carrying sperm fertilises the egg. Hence, it is determined by the father.