Science (086) — AI-generated practice question

Cross Diagram:

| | X (from mother) | X (from mother) |
|---|---|---|
| X (from father) | XX (Girl) | XX (Girl) |
| Y (from father) | XY (Boy) | XY (Boy) |

Father determines sex: The mother always contributes an X chromosome to the child. The father can contribute either X or Y. If the child inherits X from the father → girl (XX); if Y → boy (XY). So the sex of the child depends on the father's contribution, not the mother's.

Equal probability: Since a father produces equal numbers of X-bearing and Y-bearing sperms, the chance of fertilisation by either type is equal (50:50), making the probability of a boy equal to the probability of a girl.

Source: Chapter 8, Section 8.2.4 – Sex Determination

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• The cross diagram (Punnett square) is essential — examiners expect it drawn/tabulated clearly.
• Key point: mother is always XX → always gives X; father is XY → gives X or Y randomly.
• "Father determines sex" must be explicitly stated with reasoning, not just implied.
• The 50:50 probability comes from equal production of X and Y sperms — mention this directly.
• All three parts carry marks, so answer each one clearly.