UPSC CDS 2 2020 GK Paper

Concept:Human sex is determined by the combination of sex chromosomes ($\mathrm{X}$ and $\mathrm{Y}$) inherited from each parent.Explanation:Human cells normally have 23 pairs of chromosomes, including one pair of sex chromosomes.Females have two $\mathrm{X}$ chromosomes ($\mathrm{XX}$), while males have one $\mathrm{X}$ and one $\mathrm{Y}$ chromosome ($\mathrm{XY}$).A mother always contributes an $\mathrm{X}$ chromosome to her child.A father contributes either an $\mathrm{X}$ or a $\mathrm{Y}$ chromosome.If the child receives an $\mathrm{X}$ from the father, the pair becomes $\mathrm{XX}$ — resulting in a female.If the child receives a $\mathrm{Y}$ from the father, the pair becomes $\mathrm{XY}$ — resulting in a male.Therefore, for a normal female child, the required chromosomes are one $\mathrm{X}$ from the mother and one $\mathrm{X}$ from the father.This matches option A.Answer:Option A – one $\mathrm{X}$ chromosome from mother and one $\mathrm{X}$ chromosome from father.