A heterozygote advantage is when the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype. This is due to a single locus known as overdominance, which is a condition where the phenotype of the heterozygote lies outside the phenotypical range of both homozygote parents, and heterozygous individuals have a higher fitness than homozygous individuals (1,2). The advantages and disadvantages are often complicated, because more than one gene may influence a given trait. Major genes usually have multiple effects which can simultaneously convey separate advantageous traits and disadvantageous traits, while both homozygotes convey a disadvantage.

Heterozygote advantage is a major mechanism for "hybrid vigor" which is the improved or increased function of any biological quality in a hybrid offspring. A majority of cases- especially in plants- are due to dominance and the masking of deleterious recessive alleles by wild-type alleles. But, there were also findings of overdominance, especially in rice. Recently, research has established that there is an epigenetic contribution to heterozygote advantage (3,4).


  1.  Charlesworth D, Willis JH (November 2009). "The genetics of inbreeding depression".Nat. Rev. Genet. 10 (11): 783–96. doi:10.1038/nrg2664. PMID 19834483.
  2. Carr DE, Dudash MR (June 2003). "Recent approaches into the genetic basis of inbreeding depression in plants". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 358(1434): 1071–84. doi:10.1098/rstb.2003.1295. PMC 1693197. PMID 12831473.
  3. Chen ZJ (February 2010). "Molecular mechanisms of polyploidy and hybrid vigor".Trends Plant Sci. 15 (2): 57–71. doi:10.1016/j.tplants.2009.12.003. PMC 2821985.PMID 20080432.
  4. Baranwal VK, Mikkilineni V, Zehr UB, Tyagi AK, Kapoor S (November 2012)."Heterosis: emerging ideas about hybrid vigour". J. Exp. Bot. 63 (18): 6309–14.doi:10.1093/jxb/ers291. PMID 23095992.

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