A strong understanding of the difference between gene and allele is needed now. We covered allele interactions in the lesson before this one. Allele interactions deal with a single gene and its alleles. Alleles, versions of a gene, can interact when placed together in a heterozygote.
We are now looking at two genes and how they interact. To more easily understand how two genes interact, we will only be considering the normal alleles and null alleles of both genes. Normal alleles will be dominant, null alleles will be recessive. In addition, the two genes are UNLINKED. The various interactions are made evident in standard F2 generations: Two purebred parents are crossed, a dihybrid F1 is formed, the dihybrid F1 is selfed, and F2 generation is examined. One must remember, the progeny of dihybrid selfs are always in a fixed genotype distribution: 9 A _ B_ : 3 A _ bb : 3: aa B _ : 1 aa bb. BUT, with genes interacting the phenotypic ratios are changed.
Please focus on how genes interact. You do not need to know specific pathways or organisms.
Answer the following questions.
2. There is a hypothetical plant called rat-ear. Red and pink varieties flourish in Hawaii and Long Island, NY. All the red and pink varieties can be bred true. Surprisingly, when the Hawaiian pink is bred with the Long Island pink, all the resulting progeny are red. When these red progeny are selfed the next generation has 333 red flowered and 259 pink flowered plants. The breeders breathe a sigh of relief. What do the breeders understand about the petal pigmentation of rat-ear plants?