Question

Multiple alleles are present
(a) At different loci in the same chromosome
(b) In different chromosomes.
(c) At the same locus is one type of chromosome.
(d) None of the above.

Answer 1

Hint: This is the condition when three or more alleles are present for a particular gene in the same place. The phenomenon of multiple allelism is a genetic variation arising usually through mutation and therefore is responsible for hereditary variations.

Correct step by step answer:
Multiple alleles are present at the same locus as one type of chromosomes. The pairs of genes occupying a specific spot called locus on a chromosome are known as alleles.
Generally, in a diploid organism, there are only two alleles for one gene. A condition when there is a gene existing in more than two allelic forms then the condition is referred to as multiple allelism. The term ‘multiple alleles’ is referred to as the presence of three or more alleles for a particular gene. These alleles are present on the same locus of the homologous chromosome.
In humans, the condition of multiple allelism is best illustrated by the ABO blood group system. In the ABO blood group system in humans, a gene I i.e. isohemagglutinin exists in three allelic forms. They are IA, IB, and IO. Here, IA and IB are codominant and they are responsible for type A and type B antigens, respectively, on the surface of the cell; erythrocytes. The IO is a recessive allele and does not produce antigen. Now it should be noted that even if there are more than two alleles present in the population, the individual comprising the population would possess only two such alleles. Thus, we can say that in the case of ABO blood group system, the inheritance of IA and IB alleles results in having a blood type AB. The multiple alleles can be detected only in a population. The formula to find the number of genotypes for multiple allelism is (n/2)(n+1) where n is the number of alleles.
So, the correct option is ‘(c) At the same locus is one type of chromosomes’.

Note:
- The term ‘multiple alleles’ is referred to as the presence of three or more alleles for a particular gene.
- Multiple allelism is a genetic variation that arises usually through mutation and therefore is responsible for hereditary variations.
- If there are more than two alleles present in a particular population, the individual comprising the population would possess only two such alleles.