Science — CBSE Class 10 board question

Flow Chart:

$$\text{Father (XY)} \xrightarrow{\text{produces}} \begin{cases} \text{Sperm with X} \\ \text{Sperm with Y} \end{cases}$$

$$\text{Mother (XX)} \xrightarrow{\text{produces}} \text{Egg with X only}$$

• X sperm + X egg → XX → Girl
• Y sperm + X egg → XY → Boy

Since the mother always contributes X, the sex of the child depends on whether the father contributes X or Y chromosome. Thus, the father is responsible for determining the sex of the child.

Source: Chapter 8, Section 8.2.4 – Sex Determination

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• The examiner wants a flow chart (arrows showing the cross) plus a one-line conclusion — both are needed for full 2 marks.
• Key point: mother is always XX, so only the paternal chromosome (X or Y) decides the sex.
• Avoid writing long paragraphs; the flow chart itself carries most marks here.