Give an account of Codominance `(1 : 2 :1)`

Explanation

(i) Definition : This patterm occurs due to simultaneous expression of both alleles in the heterozygote. The phenomenon in which two alleles are both expressed in the hetorozygous individual is known as codominance.
Example: Red and white flowers of camellia, inheritance of sickle cell hemoglobin, ABO blood group system in human beings.
(ii) In human beings `I^(A)`and `I^(B)` alleles of I gene are codominant which follows Mendels law of segreegation.
(iii) Codominance in plants demonstrasted in plants with the help of electrophoresis or chromatography for protein or flavonoid substance.
Example: Gossypium hirsutum and Gossypium strutianum their `F_(1)` hybrid (amphiploid) was tested for seed protein by electrophoresis.
(iv)Both the parents have different banding patterns for their seed proteins.
(v) In hybrids, additive banding pattern was noticed.
(vi) Their hybrid shows the presence of both the types of proteins similar to their parents.
Conclusion:
(i) The hetorozygote genotype gives rise to a phenotype distinctly different from either of the homozyhote genotypes.
(ii) The `F_(1)` hetorozygotes produce a `F_(2)` progeny in a phenotype and genotype ratio of `1 : 2 : 1`.