Question

Multiple alleles are present

• A. at the same locus of the chromosome
• B. on non-sister chromatids
• C. on different chromosomes
• D. at different loci on the same chromosome.

Answer 1

Answer: (A)

at the same locus of the chromosome

Answer 2

Multiple alleles refer to the presence of more than two alternate forms of a gene that should be accommodated on two loci on a homologous pair. This is facilitated by the presence of more than one allele on the same locus of a chromosome provided one allele is present at a locus at a time.

Important Notes on the Concept:

• In humans, the condition of multiple allelism is best illustrated by the ABO blood group system.
• In the ABO blood group system in humans, gene I i.e. isohemagglutinin exists in three allelic forms. They are IA, IB, and IO.
• IA and IB are codominant and they are responsible for type A and type B antigens, respectively, on the surface of the cell; erythrocytes.
• IO is a recessive allele and does not produce antigens.
• Even if there are more than two alleles present in the population, the individual comprising the population would possess only two such alleles.
• In the case of ABO blood group system, inheritance of IA and IB alleles results in having a blood type AB.
• The formula to find the number of genotypes for multiple allelism: (n/2)(n+1) where n is the number of alleles.