3.2 Genetic Variation

When the extra-leg deformity is due to genetics, the model of frog development looks like one of these two (I’m not saying which):

A pair of tables side-by-side, both with the same design. Top row is Genotype, with columns for f f, f f-prime, and f-prime f-prime. Bottom row is Phenotype, illustrated with cartoon frogs and text labels. In the first table, genotypes f f and f f-prime have a phenotype of 4 legs and genotype f-prime f-prime has a phentype of 5 legs. In the second table, genotype f f has a phenotype of 4 legs and genotypes f f-prime and f-prime f-prime have a phentype of 5 legs.

When the variation in leg number is genetic, individuals that inherit two copies of a deleterious allele (left)—or one or two copies (right)—develop five legs. All other individuals grow four legs.

The difference between ponds in the frequency of five legs is due to the fact that one of the ponds holds frogs with a higher frequency of the f’ allele.