The diagram below shows the Dobzhansky-Muller model of the evolution of reproductive isolation. The F₁ hybrids between the species at the end of this process have reduced fitness. Which of the following genotypes have reduced fitness?

Question

Quizplus · Accepted Answer

In the Dobzhansky-Muller model, reproductive isolation arises due to the accumulation of incompatibilities between genes that have diverged in the two populations/species. In this case, the two populations/species have fixed different alleles at two loci, resulting in four possible genotypes: AAbb, aaBB, AaBb, and aabb. The hybrids between the two species (e.g. F₁) have one allele from each population/species at each of these loci and are therefore AaBb. It is in these hybrids that the incompatibility arises, resulting in reduced fitness. Therefore, the answer is C (AaBb). The other genotypes may or may not have reduced fitness, depending on the specific alleles involved and the selective pressures acting on the populations/species.

The Diagram Below Shows the Dobzhansky-Muller Model of the Evolution