What is a Punnett square?

A grid that shows every combination of one parent’s gametes with the other’s, so you can work out the probability of each genotype and phenotype.

Why is the ratio 3 : 1?

Crossing two heterozygous parents (Tt × Tt) gives TT, Tt, Tt and tt. Three of the four show the dominant trait.

The gene is on the X chromosome. Boys have only one X, so a single recessive allele is enough.

🧬 Biology · The science of living things

Two parents, four boxes, and the odds of every child.

The greenhouse

Ready to explore

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Punnett square

Breed them

Cross—

Expected ratio—

Offspring—

You got—