Mechanisms of Dominance (Gibert, S. F. Developmental Biology
Sixth Edition. Swarthmore College. Sinauer Associates, Inc. Publishers,
Sunderland, Aassachusetts U.S.A.)
There are at least 3 ways of achieving a dominant phenotype:
1) Gain of Function Mutations - this is a mutation that
causes a reception for the production of a protein to be constitutively active
(it is always active). This activity is sufficient to cause an abnormal/new
phenotype to develop. Gain of function mutations are dominant.
2) Haploinsufficiency - 1 copy of the gene is not sufficient
to produce the required amount of product for normal/regular development (the
heterozygote and the homozygous mutants are dominant to the wild type
genotype).
3) Dominant Negative Allele - This can occur when the active
form of the protein is a multimer and in order for the protein to function in a
wild type fashion, all proteins of the multimer have to be wild type.
Definitions (Gibert, S. F. Developmental Biology Sixth
Edition. Swarthmore College. Sinauer Associates, Inc. Publishers, Sunderland,
Aassachusetts U.S.A.)
Genetic Heterogeneity - When mutations in different genes
produce similar phenotypes.
Pleiotrophy - The production of several effects by one gene
(e.g. 1 gene has an effect on several different systems/developmental
pathways).