Sex determination


  1. Ordinary human body cells contain 23 pairs of chromosomes.
  2. 22 pairs control characteristics only, but one of the pairs carries the genes that determine sex.
    • In females the sex chromosomes are the same (XX).
    • In males the chromosomes are different (XY).
    • Students should be able to carry out a genetic cross to show sex inheritance.
    • Students should understand and use direct proportion and simple ratios in genetic crosses.

Use ratios, fractions and percentages,

Understand and use the symbols: =, <, <<, >>, >, ∝, ~