What is Difference Between Codominance And Incomplete Dominance

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Incomplete Dominance is an Intragenic (Allelic) Gene Interaction, where there is no clear-cut dominant-recessive relationship between the two alleles of a gene. Both the alleles express partially, often creating an intermediate phenotype. Example: Pink flower in Mirabilis Jalapa, when crossed with Red and White flower plants.

Co-Dominance is also an Intragenic (Allelic) Gene Interaction, where both the co-dominant alleles express fully, causing a mixture of effects in the resulting phenotype. Example: Roan Character in cattle and Blood Group (AB) which is the resulting phenotype of (A) and (B) alleles of blood group. ABO blood group system displays the three gene interactions - Complete Dominance, Codominance and Multiple Alleles

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Table of Differences between Codominance and Incomplete Dominance

Incomplete DominanceCo-Dominance
Effect of one of the two alleles is more conspicuous.Effect of both the alleles are equally conspicuous.
It produces a fine mixture of the expression of two alleles.There is no mixing of the expression of two alleles.
The effect in hybrid is intermediate of the two alleles.Both the alleles produce their effect independently.
The expressed phenomenon is new. It has no allele of its own.The expressed phenotype is combination of two phenotypes and their alleles.
The incomplete dominant allele has quantitative effect.The quantitative effect is absent.
Examples: Mirabilis Jalapa; SnapdragonExamples: A and B blood group alleles of Human; Roan character in Cattle

Gene Interactions

Both the Complete and Incomplete Dominance are the Intragenic (Allelic) Gene Interaction. The other types are:
  • Intragenic (Allelic) Gene Interaction
  • Intergenic (Non-Allelic) Gene Interaction
    • Epistasis
    • Duplicate Genes
    • Complementary Genes
    • Supplementary Genes
    • Polymeric Genes
    • Pleiotropy
    • Polygenic Genes

Multiple Choice Questions

ABO Blood group system is an example of
(1) Complete dominance and multiple allele
(2) Complete dominance and Lethal genes
(3) Co-dominance and multiple allele
(4) Incomplete dominance and multiple allele

Ans: http://zoomgenetics.apphb.com/?id=m10

Which of the following is FALSE, if
DA = Dominant Allele
RA = Recessive Allele
CA = Co-Dominant Allele
DP = Dominant Phenotype
RP = Recessive Phenotype
(1) DA + RA = DP
(2) CA + RA = DP
(3) CA + RA = RP
(4) RA + RA = RP

Ans: http://zoomgenetics.apphb.com/?id=m16

`Inflated` pod shape in pea plant is a 
(1) Co-dominant allele
(2) Dominant allele
(3) Recessive allele
(4) Multiple allele

Ans: http://zoomgenetics.apphb.com/?id=m19

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