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)?

half red and half white

all white

all red

unable to determine

If both the parents have progeny with red seeds and white seeds in the ratio 3:1 then it implies that both the parents are phenotypically having all red seeds while their genotype will be Rr & Rr i.e. heterozygous.

The reason why they produced progeny with white seeds even though they both are having all red seeds is because they both have one recessive allele (r) which was masked by their dominant allele (R) in them but when they were crossed some of the progeny which received both the recessive alleles (rr) produced white seeds because those progeny did not have dominant allele (R) which could mask the expression of recessive allele. In rest of the progeny, there was at least one dominant allele which did not let recessive allele to express and all those progeny produced red colored seed.

The Punnett square diagram is attached.

It is clear from the diagram that 3 (RR, Rr & Rr) out of the 4 probable progeny have red seeds while only 1 (rr) has white seeds so red: white ratio is 3:1