Canalisation (genetics)

Canalisation is the measure of a ability of a population to throw the same phenotype regardless of variability of its environment or genotype. it is for a make of evolutionary robustness. The term was coined in 1942 by C. H. Waddington to capture the fact that "developmental reactions, as they occur in organisms made to natural selection...are adjusted so as to bring about one definite end-result regardless of minor variations in conditions during the course of the reaction". He used this word rather than robustness to take into account that biological systems are non robust in quite the same way as, for example, engineered systems.

Biological robustness or canalisation comes approximately when developmental pathways are shaped by evolution. Waddington filed the concept of the epigenetic landscape, in which the state of an organism rolls "downhill" during development. In this metaphor, a canalised trait is illustrated as a valley which he called a creode enclosed by high ridges, safely guiding the phenotype to its "fate". Waddington claimed that canals form in the epigenetic landscape during evolution, & that this heuristic is useful for understanding the unique attribute of biological robustness.

Genetic assimilation

Waddington used the concept of canalisation to explain his experiments on crossveinless phenotype. He then selected for crossveinless. Eventually, the crossveinless phenotype appeared even without heat shock. Through this process of genetic assimilation, an environmentally induced phenotype had become inherited. Waddington explained this as the sorting of a new canal in the epigenetic landscape.

It is, however, possible to explain genetic assimilation using only quantitative genetics as well as a threshold model, with no address to the concept of canalisation. However, theoretical models that incorporate a complex genotype–phenotype map have found evidence for the evolution of phenotypic robustness contributing to genetic assimilation, even when alternative is only for developmental stability and non for a specific phenotype, and so the quantitative genetics models do not apply. These studiesthat the canalisation heuristic may still be useful, beyond the more simple concept of robustness.