In some families, either rural or urban, females are tortured for giving birth to a female child. They do not seem to understand the scientific reason behind the birth of a boy or a girl. In fact the mother is not responsible for the sex of the child and it has been genetically proved that the sex of a newborn is determined by what the child inherits from the father.
Read the case carefully and answer the questions that follow.
Generated by claude-sonnet-4-6 · 2026-06-15 06:53 · grounding stimulus
Model Answer
(a) The sex of a newborn is determined by the type of sex chromosome inherited from the father. If the child inherits an X chromosome from the father, it is a girl (XX); if it inherits a Y chromosome, it is a boy (XY).
(b) In males, the two sex chromosomes are X and Y, which are not perfectly homologous — they differ in size and genetic content. Hence, they are called a mismatched pair.
(c) During gamete formation (meiosis), the chromosome number is halved — each gamete carries only one set (haploid, n). When the male gamete (n) fuses with the female gamete (n) during fertilisation, the original diploid number (2n) is restored in the progeny.
Source: Heredity and Evolution, Sex Determination / Chromosomes and Sex
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Explanation
- (a) Examiners want mention of the father's contribution (X or Y) and the resulting XX/XY combination.
- (b) Key phrase is "mismatched" — X and Y differ in size and gene content; one mark for stating this clearly.
- (c) This is a 2-mark answer: name meiosis (halving) + fertilisation (restoration). Both steps must be mentioned for full credit.