Question

Suppose you have monohybrid snapdragons in your garden and you find that they produce red seeds to white seeds in the ratio of 3:1. If the alleles are designated R (red seeds) and r (white seeds), what are the probable phenotypes of the parents (P1)?

Answer 1

Bam! Reverse Punnet Square to the rescue! So, the white seeds have to be rr, while the red ones could be RR or Rr. So, since there are rr seeds and each parent plant must have an r, but since three of the 4 offspring have at least 1 R, each parent must be Rr and thus be plants that were grown from red seeds. Good to distinguish that the answer is plants from red seeds (the phenotype) not Rr (the genotype), technically.