- Ordinary human body cells contain 23 pairs of chromosomes.
- 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: =, <, <<, >>, >, ∝, ~