Question

Your alien friend from planet Xenon is visiting and wants to learn how to breed pea plants. You show your friend a recent batch of pea plants with purple flowers that you grew by crossing plants that had purple flowers with plants that had white flowers. Your alien friend is confused as to why your plants all have purple flowers. How would you explain, in the simplest way possible, what happened?

Answer 1

I think that it is because purple is the more dominant color
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Answer 2

You have a trait (plant color) and you have two possible outcomes for it (purple and white). You know that some alleles for white were present in one of the parent plants, so you know they must be present in the offspring too. But they're expression is covered up by the purple alleles from the other plant, so you know that purple is dominant to white.