Question

What did Mendel cross pollination of pea plants prove

Answer 1

That you can predict the outcome of two chromosomes mixing depending on whether or not the chromosomes are heterozygous or homozygous. For example an PPxPP cross would have a 100% chance of being purple while a ppxpp cross would have a 100% chance of being white

Answer 2

That pea plants have both male and female reproductive organs. As a result, they can either self-pollinate themselves or cross-pollinate with another plant. In his experiments, Mendel was able to selectively cross-pollinate purebred plants with particular traits and observe the outcome over many generations.