In tomatoes, red fruit (r) is dominant to yellow fruit (r). a true breeding red-fruited plant is bred to a true-breeding yellow-fruited plant.  what phenotypic ratio would you expect to see in the f1 offspring?

We make a Punnett square. A red-fruited plant will have the genotype Rr or RR. Since it says "true-breeding", it would be RR. A yellow-fruited plant would have the genotype rr. Therefore, we cross RR and rr.

The result would give you 100% Rr, meaning that the phenotypic ration would be 4 red: 0 yellow