Question

A population is said to be polymorphic for a locus if it has at least
A. Three genotypes for that locus
B. Two genotypes for that locus
C. Two genotypes for that locus, the rarest of which is more common than expected by
mutation alone.
D. None of the above

Answer 1

Hint:Gene polymorphism is a phenomenon in which more than one allele occupies a gene’s locus within a population. They can occur in any region of the genome. The majority of the gene polymorphisms are silent and do not alter the function or expression of genes.

Complete answer:
● According to the definition, the population of genes is said to be polymorphic if it has more than one allele at a single locus.
● So at least two genotypes for that locus will cause polymorphism in the population.
● The frequency of allele plays an important role in determining polymorphism.
● If allele frequency is less than 1% then there are high chances of mutations.
● Polymorphism can also occur at low allele frequency but mutation chances are high at that allele frequency.
● So allele frequency should be more than 1% to have stable polymorphism.
● Examples of Gene polymorphism include Major Histocompatibility Complex (MHC).
● Three genotypes for that locus will also cause gene polymorphism but the question has asked about the minimum genotype for the locus to cause polymorphism
● Two genotypes for that locus, the rarest of which is more common than expected by mutation alone. This is wrong. Despite saying two genotypes it is asking about a mutation that occurs below 1% allele frequency and to cause gene polymorphism in a population, allele frequency should be more than or equal to 1%..
So, the correct option is (B) Two genotypes for that locus.

Note: Polymorphism can be identified by various methods such as PCR (Polymerase Chain Reaction) which causes amplification of genes. PCR is the best tool to distinguish between Mutation and Polymorphism.