Because dominance is incomplete in this example the usual 3:1 ratio is modified to a 1:2:1 ratio.

In peas the allele for round seeds (R) is dominant over wrinkled seeds (r), and yellow seed color (Y) is dominant over green (y). A plant with yellow round seeds is crossed with a plant with green wrinkled seeds. The progeny all have yellow seeds, but half have wrinkled seeds. What was the genotype of the round seeded parent: