Incomplete dominance

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Incomplete dominance occurs when a genotype is heterozygous for two different alleles, but one allele is not dominant over the over; the phenotype shown is intermediate between the two penhotypes of the homozygous allele genotypes. Not to be confused with co-dominance, during which the phenotype shows both characteristics of the homozygous genotypes.

For example, in the flower Antirrhinum majus, petals will be red if the genotype is homozygous for the red allele (II), or could be ivory if the genotype is homozygous for the ivory (ii) allele. If, however, the genotype is heterozygous for both the red and ivory alleles (Ii), the phenotype will be pink (an intermediate colour between red and ivory). Had the alleles been co-dominant, the phenotype would have shown both red and ivory in a pattern (Hartl et al (2012):104)[1].


  1. Hartyl et al (2012), Genetics: Analysis of Genes and Genomes, 8th edition, United States of America, Jones and Bartlett Learning.
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