Question

With the help of one example, explain the phenomenon of codominance and multiple allelism in the human population.

Answer 1

In the field of genetics, the term dominance refers to the phenomenon by which, an allele, masks the expression of another allele when both of it are present together. Where the allele which masks the effect of the other is known as the dominant allele and the one which gets masked over is known as the recessive allele.

Step by step answer: Co-dominance is the phenomenon by which in a gene when two different alleles are present, both of it gets expressed together, i.e, both the alleles get equally dominant. It occurs in a heterozygotic genotype. The trait becomes neither dominant nor recessive. Multiple allelism occurs, when in a condition, wherein a gene three or more alleles are present. Alleles are known as a pair of genes present in the locus of a chromosome. If a gene exists with two or more allelic forms, it is referred to as multiple allelism. In human beings, both codominance and multiple alleles occurs in the ABO grouping of blood. The different blood groups in human beings are coded by a gene named I, it consists of mainly three alleles, namely IA, IB, and IO, where A, B, and O are the various alleles present, and the different combination of the genes consisting of these alleles, are responsible for the different blood groups. Codominance occurs when the alleles IA and IB are present together. Both these alleles are dominant together, that is, if present together it results in the AB blood group, while the allele Io is recessive to A and B alleles.

Note: Pleiotropy is a phenomenon by which a single gene is responsible for more than one phenotypic traits, which are not related to each other. In short, it has multiple phenotypes. One disorder in humans occurring due to pleiotropy is phenylketonuria.