Name: Pleiotropy
Uploaded: 2019-07-19
Duration: 5 min 21 s
Description: Phenylketonuria is a disease that is affected by the phenomenon of pleiotropy. Learn more about this genetic change occurring in our body through this video.

Question

'The human ABO blood group is considered a good example of co-dominance and multiple alleles'. Analyse the statement by giving suitable reasons.

Accepted Answer

A gene has two alternative forms/versions called alleles. They are present at the same locus in a pair of homologous chromosomes. Two alleles of a gene can form three genotypes in a diploid organism. Sometimes a gene may have more than two alleles. Although humans as diploid organisms can have only two alleles for any given gene, multiple allele traits may exist at the population level. When more than two alleles exist in a population of a specific gene, the phenomenon is called multiple alleles.

ABO blood group is a good example of multiple alleles as the expression of all the blood types occurs by three alleles of a single gene, which can produce six genotypes. The phenomenon of multiple alleles is mentioned in a tabulated form below.

Genotype Antigens present on red blood cells Antibodies present in blood plasma ABO blood group phenotype Blood types that can be accepted Blood types that can accept blood for transfusion

I^AI^A A Anti-B Type A A and O A and AB

I^Ai A Anti-B Type A A and O A and AB

I^BI^B B Anti-A Type B B and O B and AB

I^Bi B Anti-A Type B B and O B and AB

I^AI^B A and B Neither anti-A nor anti-B Type AB A, B, AB and O AB only

ii Neither A nor B Anti-A & anti-B O only O only A, B, AB and O

The A and B antigens are actually carbohydrate groups (sugar polymers) that are bound to lipid molecules (fatty acids) protruding from the plasma membrane of the red blood cell. They are also called isoagglutinogens because they cause blood cell agglutination in the case of incompatible blood transfusions.

In general, if the alleles are different, the dominant allele will be expressed, while the effect of the other allele, called recessive, is masked. In co-dominance, neither of the alleles is recessive, and the phenotypes of both alleles are expressed.

One classic example of co-dominance and multiple alleles is the human blood group. If the offspring inherits both A and B alleles from its parents, then its genotype can be AB and will express both the alleles, which is a case of co-dominance. Here, the characteristic of both A and B alleles is expressed.

'The human ABO blood group is considered a good example of co-dominance and multiple alleles'. Analyse the statement by giving suitable reasons.

Important Questions on Principles of Inheritance and Variation

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