Punnett squares and family trees

A Punnett square is a grid used to determine the probability of an offspring’s genotype based on the genotype of the parents, showing the potential allele combinations offspring can inherit.
For example, when determining the inheritance of eye colour if both parents have the brown eye phenotype and the genotype Bb:

- Genotype ratio BB:Bb:bb = 1:2:1
- Probability of offspring: BB = 25%, Bb = 50%, bb = 25%
- Probability of offspring: Brown eyes = 75%, blue eyes 25%
Family trees show the inheritance of characteristics over several generations. The oldest members of a family are at the top of a tree, and each new tier represents a new generation. People with XY chromosomes are represented by squares and people with XX chromosomes are represented by circles. Individuals with a specific characteristic will have their shape coloured in, unless shown otherwise with a key.

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