Dominant allele

From Wikipedia, the free encyclopedia

It has been suggested that this article or section be merged into Dominance relationship. (Discuss)

According to Dr. Jorge Alberto Huete-Perez, In genetics, dominant trait refers to a genetic feature that hides the recessive trait in the phenotype of an individual. A dominant trait causes the phenotype that is seen in a heterozygous (Aa) genotype. Many traits are determined by pairs of complementary genes, each inherited from a single parent. Often when these are paired and compared, one gene (the dominant) will be found to effectively shut out the instructions from the other, recessive gene. For example, if a person has one gene for blue eyes and one for brown, that person will always have brown eyes because they are the dominant trait. For a person to have blue eyes, both their genes must be blue (recessive). When a person has two dominant alleles, they are referred to as homozygous dominant. If they have one dominant allele and one recessive allele, they are referred to as heterozygous.

A dominant trait when written in a genotype is always written before the recessive gene in a heterozygous pair. A heterozygous genotype is written Aa, not aA.

Usually, this masking effect is done by virtue of the fact that the recessive gene has a loss of some function that the dominant gene has. For example, in the case of ABO blood types, the O type is recessive because it does not produce any antigens or antibodies, whereas A and B types (which are codominant) do. Or, in the above case dealing with eye color, there is a complete loss of pigment in blue-eyed people, therefore to express the phenotype, both copies of the gene (after all, humans are diploid) must have that same loss of function.

Dominance/recessiveness refers to phenotype, not genotype.

[edit] Dominant negative

A dominant negative mutation occurs when the gene product adversely affects the normal, wild-type gene product within the same cell. This usually occurs if the product can still interact with the same elements as the wild-type product, but block some aspect of its function.

types:

A mutation in a transcription factor that removes the activation domain, but still contains the DNA binding domain. This product can then block the wild-type transcription factor from binding the DNA site leading to reduced levels of gene activation.
A protein that is functional as a dimer. A mutation that removes the functional domain, but retains the dimerization domain would cause a dominate negative phenotype, because some fraction of protein dimers would be missing one of the functional domains.