Incomplete Dominance: Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles. Unlike complete dominance inheritance, one allele does not dominate or mask the other. Incomplete dominance occurs in the polygenic inheritance of traits such as eye color and skin color. It is a cornerstone in the study of non-Mendelian genetics.

• Incomplete dominance is also called partial dominance or semi-dominance.
• In incomplete dominance, both the alleles in heterozygous condition partially express themselves.
• Here the dominant allele can not completely mask the effect of recessive alleles.
• The physical appearance of the organism shows the blending of both the two alleles i.e. dominant allele as well as recessive allele.

Mechanism of Incomplete Dominance

Incomplete dominance occurs because neither of the two alleles is completely dominant over the other. This results in a phenotype that is a combination of both.

Gregor Mendel conducted experiments on pea plants. He studied on seven characters with contrasting traits and all of them showed a similar pattern of inheritance. Based on this, he generalized the law of inheritance.

Later, researchers repeated Mendel’s experiment on other plants. Shockingly, they noted that the F₁ Generation showed variation from the usual pattern of inheritance. The monohybrid cross resulted in F₁ Progeny which didn’t show any resemblance to either of the parents, but an intermediate progeny.

Examples of Incomplete Dominance

• Cross pollination between red snapdragon and white snapdragon result in pink snapdragon.
• Here, neither the white allele or red allele is dominant.
• The pink colour results from the blending of both the two alleles that are white allele or white and red allele.
• RR represents the dominant red allele and rr represents the recessive allele.
• In F₁ ( filial 1 ) generation, all the offspring will be of pink colour having genotype Rr.
• And in F₂ generation when two heterozygotes are crossed and results in 1 red coloured snapdragon, 2 pink coloured snapdragon and 1 white coloured snapdragon in the ratio 1:2:1.

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By Team Learning Mantras