Overdominance

Overdominance

Overdominance is a condition in genetics where the phenotype of the heterozygote lies outside of the phenotypical range of both homozygote parents. Overdominance can also be described as heterozygote advantage, wherein heterozygous individuals have a higher fitness than homozygous individuals.

An example in humans is sickle cell anemia. This condition is determined by a single polymorphism. Possessors of the deleterious allele have lower life expectancy, with homozygotes rarely reaching 50 years of age. However, this allele also yields some resistance to malaria. Thus in regions where malaria exerts or has exerted a strong selective pressure, sickle cell anemia has been selected for its conferred partial resistance to the disease. While homozygotes will have either no protection from malaria or a dramatic propensity to sickle cell anemia, heterozygotes enjoy a partial resistance to both.[citation needed]

Contents

The Gillespie Model

Population Geneticist John H. Gillespie established the following model [1]:

Genotype: A1A1 A1A2 A2A2
Relative fitness: 1 1-hs 1-s

Where h is the heterozygote effect and s is the recessive allele effect. Thus given a value for s (ie: 0<s<1), h can yield the following information:

h=0 A1 dominant, A2 recessive
h=1 A2 dominant, A1 recessive
0<h<1 incomplete dominance
h<0 overdominance
h>1 Underdominance

For the case of sickle cell anemia the situation corresponds to the case h<0 in the Gillespie Model .

See also

Notes

  1. ^ Gillespie 2004

References



Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • overdominance — overdominance. См. отрицательный эффект двойной дозы. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • overdominance — superdominavimas statusas T sritis augalininkystė apibrėžtis Alelinių genų sąveika, kai heterozigotiniai individai požymių raiška lenkia homozigotinius individus. atitikmenys: angl. overdominance; superdominance rus. сверхдоминирование …   Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

  • overdominance — noun Date: 1947 the condition wherein a heterozygote produces a phenotype more extreme or better adapted than that of the homozygote • overdominant adjective …   New Collegiate Dictionary

  • overdominance — o·ver·dom·i·nance (ō vər dŏmʹə nəns) n. The condition of a heterozygote having a phenotype that is more pronounced or better adapted than that of either homozygote.   o ver·domʹi·nant adj. * * * …   Universalium

  • overdominance — noun The state of a gene wherein a heterozygote has a higher risk of disease than either of its homozygote parents …   Wiktionary

  • overdominance — That state in which the heterozygote has greater phenotype value and perhaps is more fit than the homozygous state for either of the alleles that it comprises. Cf.:balanced polymorphism. * * * over·dom·i·nance däm( ə) nən(t)s n the property of… …   Medical dictionary

  • overdominance — Where heterozygote performance is superior to that of either parental genotype …   Glossary of Biotechnology

  • overdominance — ˌ ̷ ̷  ̷ ̷ ˈ ̷ ̷  ̷ ̷  ̷ ̷ noun Etymology: over (III) + dominance : the property of having a heterozygote that produces a phenotype more extreme or better adapted than that of the homozygote • overdominant ¦ ̷ ̷  ̷ ̷ ¦ ̷ ̷  ̷ ̷  ̷ ̷ adjective …   Useful english dictionary

  • Dominance versus overdominance — is a scientific controversy in the field of genetics that has persisted for more than a century.[1] These two alternative hypotheses were first stated in 1908. Genetic basis of heterosis When a population is small or inbred, it tends to lose… …   Wikipedia

  • Polar overdominance — is a unique form of inheritance (described in sheep) whereby a mutant Callipyge allele must be inherited from the father to cause muscle hypertrophy (big buttocks).ee also*Imprinting (genetics)External links*… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”