The sex of the baby is genetically determined by:
AThe father's sperm — 50% carry X, 50% carry Y; the fertilising sperm decides
BThe mother's ovum, which carries either X or Y
CMaternal hormonal levels at fertilisation
DBoth equally — random chance during meiosis in the mother
Answer & Solution
Correct answer: A. The father's sperm — 50% carry X, 50% carry Y; the fertilising sperm decides
All ova carry **X** (mother is XX). Half the sperms carry **X** and half carry **Y** (father is XY). The **fertilising sperm** therefore decides sex: X-sperm → XX (girl); Y-sperm → XY (boy).
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