Final answer:
The frequency of the green allele in snapdragons can be determined from a given F2 offspring ratio of 3:1 yellow to green seeds, with the resulting frequency being 50%.
Step-by-step explanation:
The frequency of the green allele in snapdragons can be determined from the given ratio of the F2 offspring resulting from self-pollination of the F1 offspring. According to the ratio of 3:1 yellow to green seeds, we understand that yellow is the dominant allele while green is the recessive allele. In a simple Mendelian inheritance, a 3:1 ratio of dominant to recessive phenotypes suggests that in the F1 generation, all individuals were heterozygous, carrying one dominant and one recessive allele (Yg). Therefore, the F2 generation, which exhibits a 3:1 phenotype ratio, actually has a genotype ratio of 1YY:2Yg:1gg. To obtain the frequency of the green allele (g), we look at the homozygous recessive (gg) and the heterozygous (Yg) genotypes. Since there is one gg for every three Yg, and each Yg carries one g allele, the frequency of the green allele would be calculated by (2 x ½ number of Yg) + number of gg, divided by the total number of alleles.
If we treat the ratio as the actual number of individuals, we have 1 gg and 2 Yg for every 3 yellow seed plants. The number of green alleles would therefore be (2 x 1/2) + 1 = 2 green alleles for every 4 alleles in total, giving a green allele frequency of 2/4 or 50%.