A cross between a red-seeded Eucalyptus tree and a gray-seeded Eucalyptus tree yielded an F1 with red kernels. The F2 which resulted from intercrossing any two F1 individuals yielded a 15:1 ratio of red:gray. Provide a genetic explanation for this, including the genotypes of the two original parents, the F1, and a shorthand summary of the F2 genotypes.