haya.Learning made clear
Sex determination in humans, birds and honey bee sheet
5-mark answer frame

Explain the mechanism of sex determination in humans. How does it differ in birds and in the honey bee?

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Define the basis. Sex is decided by sex chromosomes or, in some insects, by the number of chromosome sets.
  2. 2 · Explain humans. Female 44 + XX makes 22 + X eggs; male 44 + XY makes 22 + X and 22 + Y sperm in equal numbers; male heterogamety.
  3. 3 · Draw the chart. [Diagram: parents, gametes, zygotes 44 + XX and 44 + XY, ratio 1 : 1]
  4. 4 · Explain birds. Female ZW, male ZZ; female heterogamety, so the egg decides.
  5. 5 · Explain the honey bee. Fertilised egg → diploid female (32); unfertilised egg → haploid male (16) by parthenogenesis.
  6. 6 · Link to real life. In humans the father's sperm decides sex, so blaming the mother is wrong.
  7. 7 · Close in one line. So the heterogametic parent, or fertilisation itself in bees, decides the sex of the offspring.

Scoring tip: Write 44 + XX and 44 + XY, not just XX and XY. Draw the chart neatly with gametes in circles.