Punnett Square Probability

Work the printed Tt × Tt example together before students try the four crosses. On the probability sheet, have students say aloud which boxes show the recessive trait before writing the fraction.

Fill in Punnett squares for guinea pigs, rabbits, freckles and peas, then write each chance. The directions on the page read: Write the parents' alleles on the square, the first parent across the top. Fill the square, then write the chance of the recessive trait. An answer key is included.

Yes, both. We made it for 6th Grade living things, and the page works the same whether it lands on a kitchen table or a center rotation. At home, most families go through it together and talk the answers out loud, and that talking is where most of the learning happens with punnett squares. In class it runs well as independent work while you pull a small group. Print one copy or thirty, whichever the day needs.

Write the first parent's alleles across the top and the second parent's down the side. Each box gets the letter above it and the letter beside it. Any offspring with at least one dominant allele shows the dominant trait.

A Punnett square has 4 boxes, so each box is a 1/4 chance, or 25%. Count the boxes that show the trait. Three boxes out of 4 is 3/4, or 75%.

It gives 1 TT, 2 Tt and 1 tt, which is 3 tall to 1 short, a 3:1 ratio, on the example at the top of Punnett Squares.