Both people and tomatoes come in different shapes and sizes. That is because every individual has a unique set of genetic variations—mutations—that affect how genes act and function. Added together, millions of small genetic variations make it hard to predict how a particular mutation will impact any individual. Cold Spring Harbor Laboratory (CSHL) Professor and Howard Hughes Medical Institute Investigator Zach Lippman showed how genetic variations in tomatoes can influence the way a specific mutation affects the plant. He is working toward being able to predict the effects of mutations on different tomato varieties.