A purebred tall pea plant is crossed with a purebred short pea plant. All of the

resulting offspring are fall. What does this tell you about the gene controlling pea

plant height?

This tells you that the tall pea plant possesses the dominant allele for height, that being tall. It shows that when two pea plants of different heights are crossed, you can establish which of them has the dominant allele for height. In this instance, tall is dominant and short is recessive. In order to have a short pea plant, two short purebred plants would have to be crossed or two heterozygous plants that each carry the recessive allele, or one of each!

The tall pea plant gene is dominant, and the short pea plant height is submissive. Each offspring has both genes, but since the tall gene is dominant, it is the only gene that shows up.