In garden peas, the allele for tall plants is dominant over the allele for short plants.A true-breeding tall plant is crossed with a short plant, and one of their offspring is test crossed.Out of 60 offspring resulting from the test cross, _______ should be short.

Question

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Since the allele for tall plants is dominant over the allele for short plants, the true-breeding tall plant must be homozygous dominant (TT) while the short plant must be homozygous recessive (tt). The offspring resulting from their cross would be heterozygous (Tt) and all tall. However, when one of these tall offspring is test crossed (crossed with a homozygous recessive individual), the possible genotypes of its gametes are T or t. This means that 50% of the offspring resulting from the test cross should inherit the recessive allele and be short (tt genotype). Since there were 60 offspring in the test cross, about half of them (30) should be short. Therefore, the answer is C) about 30.

In Garden Peas, the Allele for Tall Plants Is Dominant