Explain with a flow chart how the sex of a child is determined in human beings.

1. 1 · Define in one line. Sex determination is the way the sex of an individual is fixed; in humans, it is decided by genes.
2. 2 · Chromosomes. Women are XX and men are XY; the other 22 pairs match.
3. 3 · Gametes. Every egg carries X; half the sperms carry X and half carry Y.
4. 4 · Draw the chart. [Chart: XX × XY → gametes X; X and Y → XX girl, XY boy]
5. 5 · Link to daily life. The father's sperm decides the sex, so blaming a mother for having a girl is wrong.
6. 6 · Close in one line. Each child has an equal, 50% chance of being a boy or a girl.

Scoring tip: Put the gametes in circles and write girl and boy under XX and XY. Add the 1 : 1 ratio.