Genotypes: dominant? fittest?

Dominance and recessivity refer to relations between alleles (A1, A2) at a single locus (gene). If the presence of one allele (A1) masks the effect of the other (A2), then A1 is dominant over A2 [and A2 is recessive to A1].

Fitness (ability to survive and reproduce) refers to a phenotypic property of the organism. If we can directly relate this property to the genotype of the organism, then we can talk of the relative fitness (w) of genotypes (A1A1, A1A2 and A2A2).

Higher relative fitness of a genotype does not mean that the allele responsible for higher fitness is also dominant over the other allele.

Suppose that relative fitnesses are given as A1A1 = w11; A1A2 = w12 and A2A2 = w22. We may assign relative values to these, e.g., w11 = 1, w22 = 0.8 and w12 = 0.8. In other words, the homozygous genotype A1A1 is the most fit; the heterozygote A1A2 and the homozygote A2A2 are less fit.

Relative fitnesses may be depicted so: w11 >w12 = w22

Question: Is the allele carrying higher fitness (A1) dominant over or recessive to the allele carrying lower fitness (A2)?





A2 is dominant over A1 because it masks the effect of A1 (higher fitness) in the heterozygote. As a result, both A1A2 and A2A2 have the same relative fitness, 0.8.

Suppose w11 = 1, w22 = 0.9 and w12 = 0.8.

How do the alleles interact with each other? Represent this using just the symbols for relative fitness.




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