IGCSE Biology glossary
Punnett square
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
A diagram used to predict the possible genotypes and phenotypes of offspring from a genetic cross. The alleles of one parent are placed along the top and the other parent's alleles along the side, and the boxes show all possible offspring combinations.
What to include in an exam answer
Always use standard genetic symbols (capital for dominant, lower case for recessive, same letter). Show the parental genotypes, gametes, Punnett square, and offspring ratio. A clearly drawn Punnett square earns method marks even if the answer is wrong.
Example in context
Use a Punnett square to show the expected ratio of offspring when two heterozygous parents (Bb x Bb) are crossed: Offspring genotypes are BB, Bb, Bb, bb. Phenotype ratio is 3 dominant: 1 recessive.
Related syllabus topic
Inheritance