What is incomplete dominance? Give an example.

Explanation

Definition : When one allele is not completely dominant to another allele it shows incomplete dominance. Such allelic interaction is known as incomplete dominanace.
(i) Carl Corren's (1905) Experimented in 4 O' clock plant, Mirabilis jalapa. When the pure breeding homozygous red `(R^(1)R^(1))` parent is crossed with homozygous white `(R^(2)R^(2))`, the phenotype of the `F_(1)` hybrid is heterozygous pink `(R^(1)R^(2))`
(ii) The `F_(1)` heterozygous phenotype differs from both the parental homozygous phenotype. This cross did not exhibit the character of the dominant parent but an intermediate colour pink.
(iii) `F_(1)` generation produces intermediate phenotype pink coloured flower.
(iv) When pink coloured plants of `F_(1)` generation were interbred in `F_(2)` both phenotype and genotypic rations were found to be identical as `1 : 2 :1` (1 red : 2 pink : 1 white). Genotypic ratio is `1 R^(1)R^(1) : 2 R_(1)R^(2) : 1 R^(2)R^(2)`
(v) Thus the alleles themselves remain discrete and unaltered proving the Mendel's Law of Segregation. The phenotypic and genotypic ratios are the same. There is no blending of genes.
(vi) In the `F_(2)` generation `R_(1)` and `R_(2)` genes segregate and recombine to produce red, pink and white in the ratios of `1 : 2: 1`.
(vii) R1 allele codes for an enzyme responsible for the formation of red pigment. `R_(2)` allel codes for defective enzyme. `R_(1)` and `r_(2)` genotypes produce only enough red pigments to make the flower pink.
(viii) Mendel's particulate inheritance takes place in this cross which is confirmed by the reappearance of original phenotype in `F_(2)`.