Which of the following genotypes has reduced fitness in the following Dobzhansky-Muller model if the F1 hybrids between the species at the end of the process have reduced fitness?

1) aabb

2) AAbb

3) AaBb

4) aaBB

5) all of the above

aabb

Explanation:

The original population has the following alleles:

AABB

Then the population is divided in 2 halves.

population a alleles = AABB

population b alleles = AABB

Some time happens and mutations happens in both populations.

population a alleles = AaBB

population b alleles = AABb

The organisms that have the a and the b allele, have better adaptability to their enviroment. So over time we will have the following genotipes:

population a alleles = aaBB

population b alleles = AAbb

Something happens and the two populations interact. The hybrids would have the following genotype:

hybrid population: AaBb

The a and b alleless have a negative interaction (Dobzhansky-Muller incompatibility), so the organisms that have this genotype will have a reduced fitness.

The offspring of this reduced fitness species will be the following genotypes:

AABB, AaBB, AABb, AaBb, Aabb, aabb, aaBb, aaBB, AAbb

Since the a and b alleless have a negative interaction (Dobzhansky-Muller incompatibility), the organisms that have 2 a alleles and 2 b alleles (aabb), would a double negative interaction. So it is expected that the organisms that have the alleles aabb would have a reduced fitness.