pleiotropy
Wagner GP & Zhang J 2011 The pleiotropic structure of the genotype-phenotype map: the evolvability of complex organisms. Nat Rev Genet 12:204-213.
- pleiotropy is highly restricted and are more in line with the notion of variational modularity than with universal pleiotropy
- most genes in a genome are not highly pleiotropic
- the gene-trait relationship is strongly modular
- pleiotropy does not hinder the evolution of complex organisms
- the concept of the 'cost of complexity', however, should be more properly called the 'cost of pleiotropy'
- as the classical versions of the FGM assume that every mutation potentially affects all traits of an organism
- this position has been called 'universal pleiotropy'
- there is an alternative model that assumes that mutations are more structured and tend to affect only subsets of characters
- this model is variously known as 'variational modularity' or 'restricted pleiotropy'
- restricted pleiotropy is the predominant pattern
- with restricted pleiotropy, the rate of evolution depends on the degree of pleiotropy of individual mutations rather than on the complexity of the organism
- another simplification of the FGM is that the rate of evolution is limited by the arrival of new mutations, rather than by the amount of genetic variation that segregates in a population
- models that estimate the evolvability of genetically variable populations, using quantitative genetic models, come to qualitatively different results than do those that follow the FGM mutation accumulation approach
- in quantitative genetic models, the dimensionality of the phenotype does not affect the rate of evolution
- higher levels of pleiotropy are predicted to increase the rate of evolution
- evolvability depends only on genetic co-variance rather than pleiotropy per se
- the new data show that previous estimates of the cost of complexity are fundamentally flawed, because their basic assumptions are not empirically supported
- it is now recognized that:
- pleiotropy is highly restricted
- the total effect size scales more than additively with the number of pleiotropic effects
- the rate of evolution that is predicted from the FGM is a function of pleiotropy rather than of organismal complexity
- now the problem is to explain how the GPM has acquired this structure
