Term 'fitness' is pretty obvious, but, often 'fitness effects' is commonly used in many research articles in the field of evolutionary biology.

I suspect that 'fitness effects' has a different meaning than just 'fitness'. I found that it's really difficult to find the distinction between the two terms just by googling.

So, if some expert in the subject is reading, please clarify.



Fitness is some function of the probability of survival and fecundity for a given genotype. Fitness is therefore a single value per genotype.

Fitness effect

A fitness effect is a component of fitness. For example, for a given bi-allelic locus, the fitness effect of allele A is -0.05 in comparison to the allele B, meaning that the allele A is deleterious and the allele B is beneficial. There is a fitness effect for each allele, for each trait and, if you interested in genetic interaction (epistasis) and genetic-environment interaction, then there can be a fitness effect for each gene and each trait in each genotype in each environment.


It is typically common to assume a model of $n$ loci, where the fitness effects at each loci are $1$, $1-hs$ and $1-s$ for the three genotypes AA, AB and BB respectively (diploid population). $s$ is the selection coefficients and $h$ is the dominance coefficient. The fitness of the individual is often obtained by multiplying out the fitness effects at each loci. The worst possible fitness is therefore $\left(1-s\right)^n$.

  • $\begingroup$ Fitness effect of an allele seems to be an 'effect size' which is calculated relative to fitness of other allele. $\endgroup$ – Ramirez Nov 29 '17 at 5:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.