Bateson–Dobzhansky–Muller model

[6][7] For example, an ancestral species has the alleles a and b fixed in its population, resulting in all individuals having the aabb genotype.

[5] The model states that genetic incompatibility is most likely evolved by alternative fixation of two or more loci instead of just one, so that when hybridisation occurs, it is the first time for some of the alleles to co-occur in the same individual.

[8] The Dobzhansky–Muller incompatibilities can result from purely random, neutral or non-selected differences between the populations.

The genes that have arisen to adapt to different ecological surroundings can thus cause hybrid incompatibilities.

[5] The genetic changes that are accumulated when populations diverge from a common ancestor will not severely decrease viability or fertility because natural selection influences these strongly deleterious alleles.

However, natural selection cannot act when alleles have never occurred together, as they would in the genome of a hybrid.

[12] Therefore, Dobzhansky–Muller incompatibilities can also provide information on the time and type of divergence which can help in phylogenetic studies.

Figure 1. In the ancestral population the genotype is AABB. When two populations become isolated from each other, new mutations can arise. In one population A evolves into a, and in the other B evolves into b. When the two populations hybridise it is the first time a and b interact with each other. When these alleles are incompatible, we speak of Dobzhansky–Muller incompatibilities.