In garden peas, the allele for tall plants is dominant over the allele for short plants. Imagine that a true- breeding tall plant is crossed with a short plant. Then one of their offspring is test crossed. Out of 20 offspring resulting from the test cross, about how many should be tall?

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A true-breeding tall plant is homozygous dominant (TT) and the short plant is homozygous recessive (tt). Their offspring will be heterozygous (Tt). A test cross with a homozygous recessive plant (tt) will produce a 1:1 ratio of tall (Tt) to short (tt) plants. Therefore, out of 20 offspring, about 10 should be tall.

In Garden Peas, the Allele for Tall Plants Is Dominant