Overdominance
Overdominance
Overdominance (pronunciation: /ˌoʊvərdoʊˈmɪnəns/), also known as heterozygote advantage, is a phenomenon in genetics where the heterozygote genotype has a higher fitness than either the homozygote dominant or homozygote recessive genotype.
Etymology
The term "overdominance" is derived from the prefix "over-", meaning "excessive", and "dominance", referring to the principle in genetics where one allele masks the contribution of a second allele at the same locus. The term thus refers to an excessive dominance, where the heterozygote genotype is more advantageous than either homozygote genotype.
Explanation
In overdominance, the heterozygote genotype exhibits a trait that is more beneficial than either homozygote genotype. This can occur in various forms, such as increased size, speed, or resistance to disease. The exact mechanism of overdominance is still a topic of ongoing research in the field of genetics. Some theories suggest that it may be due to the interaction of different alleles at the same locus, while others propose that it may be due to the interaction of genes at different loci.
Examples
One of the most well-known examples of overdominance is the sickle cell trait. Individuals with one sickle cell allele and one normal allele (heterozygotes) have a higher resistance to malaria than individuals with two normal alleles (homozygotes). This is because the sickle cell allele causes changes in the shape of red blood cells that make it harder for the malaria parasite to invade.
Another example is the tay-sachs disease, where individuals with one Tay-Sachs allele and one normal allele (heterozygotes) have a higher resistance to tuberculosis than individuals with two normal alleles (homozygotes).
Related Terms
External links
- Medical encyclopedia article on Overdominance
- Wikipedia's article - Overdominance
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