It is important to realize that, in this experiment, the starting parent plants were homozygous for pea seed color. That is to say, they each had two identical forms (or alleles ) of the gene for this trait--2 yellows or 2 greens. The plants in the f1 generation were all heterozygous . In other words, they each had inherited two different alleles--one from each parent plant. It becomes clearer when we look at the actual genetic makeup, or genotype , of the pea plants instead of only the phenotype , or observable physical characteristics.