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5.3 Death from Fixed Mutations

Recall that the equation for the relative fitness of an individual is

where n1 is the number of heterozygous mutations in the individual, n2 is the number of homozygous mutant loci, and nf is the number of fixed mutations in the population. We can factor this into two parts: the effects due to segregating loci, and the effects of fixed loci:

where

and

One way to interpret this new equation is that of all the individuals that fail to survive, die as a result of too many segregating mutations, and die from fixed mutations. The significance of this observation is that the individuals that die from fixed mutations are going to do so no matter how many segregating mutations they carry; in other words, it is not even necessary to go through the steps of drawing random parents, combining genes, and counting mutations.