In peas, the gene for green color is dominant over the gene for yellow color.We will specify the gene for yellow peas as y, and the gene for green peas as Y. Each pea has two genes for color (one from each parent) and donates only one gene for color to its offspring. Yellow peas have the genotype yy. Any other genotype leads to green peas. Consider the following Punnett square: The offspring of these two parents
could be either green or yellow.
According to the Punnett square, the combination of genes of Parent I with the genes of Parent II results in either offspring with yy (which is yellow) or Yy (which is green).