I'm not sure how to answer this question.

Question

A geneticist notes that crossing a round radish with a long radish produces oval radishes. When oval radishes were crossed with oval radishes, the F2 generation had these phenotypes: 100 long, 200 oval, and 100 round radishes. Use symbols to explain the results obtained for the F1 and F2 generations.

Answer 1

What you're dealing with here is "incomplete dominance." That is when one allele at a two-allele locus is not fully dominant over the other. Let's say the round radish allele is R and the long radish allele is L. Either one could be "dominant" - there's not enough information to say and it doesn't matter for the purpose of this exercise.

What we're seeing is two homozygous parents (that is RR and LL) forming offspring. The round parent (RR) can only contribute an R allele for the shape trait and the long parent (LL) can only contribute an L. This means that all the offspring will have the genotype RL and the oval phenotype which is intermediate between the two parental phenotypes.

The oval radishes resulting from the first cross form the F1 generation. If two of them form offspring (which form the F2 generation) we get the classic 1:2:1 Mendelian ratio for when heterozygotes breed. That is 1 of each type of homozygote (LL or RR) for every two heterozygotes (LR). Fill in a 2 X 2 Punnett square to see why this is the case.

You can make the symbols whatever you like, but the key is to understand what incomplete dominance is and how genotype translates into phenotype.