Dominance

First, be careful when you do a google search on 'dominance'. I'm so naive sometimes.....

Anyhow, an interesting question came up today - what IS dominance? What causes one allele to be 'dominant' to another?

In certain cases it is pretty simple. The production of 'something' tends to be dominant to the production of 'nothing'. So 'wild type' alleles tend to be dominant to mutants that code for nothing. If the allele is coding for the production of an enzyme and a single copy of the allele produces more than enough then the heterozygote and the homozygote will have similar phenotypes - complete dominance. However if the homozygote produces just enough then the half expression of the heterozygote may result in a different phenotype. The pink flowers would be a good example here. The pink comes about by the production of only half as much red pigment.

After this it gets a bit more complicated and was, in fact, the subject of a fairly intense debate in the last century between two giants of the population genetics world: RA Fisher and Sewall Wright. If you are interested in this topic then here are a couple of entries into the literature: a blog post entitled ' Whatever happened to the Fisher-Wright controversy?' and an article in the Journal of Theoretical Biology on 'The Heat-shock Response and the Molecular Basis of Genetic Dominance'.

This time last year: Canterbury Tales