Two species have genotypes aaBB and Aabb.Mating between these species leads to F₁ individuals that are sterile due to a Dobzhansky-Muller incompatibility.Therefore,the genotype of the ancestral population could have been A) AaBb. B) AABb. C) aabb. D) Aabb. E) AaBB.

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The sterile offspring resulting from a Dobzhansky-Muller incompatibility implies that there are genetic incompatibilities between the two parental species. This suggests that the two parental species have been separated for a significant amount of time, during which genetic divergence occurred.

The genotypes of the parental species are aaBB and Aabb. From this, we can infer that one parental species is fixed for one allele at both loci (aaBB) while the other is heterozygous for both loci (Aabb).

If the ancestral population was either AaBb, AABb, or AaBB, we would expect some offspring to be viable (not all sterile) because they do not have genetic incompatibilities. Therefore, we can rule out these options.

The only remaining option is c) aabb, where both loci are homozygous recessive. This would result in complete genetic incompatibility with the parental species, leading to sterile offspring. Therefore, the best choice for the ancestral genotype is aabb.

Two Species Have Genotypes AaBB and Aabb