Incomplete dominance

Definition

noun

(genetics) A form of dominance occurring in heterozygotes in which the dominant allele is only partially expressed, and usually resulting in an offspring with an intermediate phenotype


Supplement

In genetics, dominance pertains to the property of a gene (or allele) in relation to other genes or alleles. A gene or allele shows dominance when it suppresses the expression, or dominates the effects, of the recessive gene (or allele). There are many forms of dominance: complete dominance, incomplete dominance, and codominance.

In incomplete dominance, a heterozygous organism carrying two alleles wherein one is dominant and the other one is recessive, (e.g. Aa), the dominant allele will only be partially expressed. Hence, the heterozygote (Aa) will have an intermediate phenotype.

A typical example is the color of the flower in which R symbolizes the dominant allele for red pigment and r is the recessive allele for no pigment. In incomplete dominance, the heterozygous plant carrying both alleles, Rr, will not be able to produce enough red pigment (since the dominant allele is only partially expressed) and therefore will appear pink.


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