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Punnett squares: the chance of a trait

Punnett squares: count the chances

Key points

1. Each parent passes on 1 letter for a gene.
2. Capital letter = dominant. Small letter = recessive.
3. Draw 4 boxes. One parent across the top, one down the side.
4. Count the boxes and turn the count into a fraction or percent.
5. Genotype = the letters. Phenotype = what you can see.

Worked example

Try it

A TT plant and a tt plant have young. What share are expected to be tall?

Answer: Every box is Tt, so 4 of 4 (100%) are expected to be tall.

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