- X and Y chromosomes
- X and Y = Men
- Y + Y = Female
- When making sperm the X and Y chromosomes are drawn apart in the first division in meiosis. There's a 50% chance each way.
- Alleles are different versions of the same gene
- In genetic diagrams letters are usually used to represent alleles
- Homozygous - two alleles for a particular gene are the same
- Heterozygous - two alleles for a particular gene are different.