Question

1. What are some factors that could affect, or allow, polymorphisms (SNPs) to be preserved in a population? What is the common explanation for a mutant phenotype’s geographical distribution.

Answer 1

The conservation of a sequence (DNA or protein) depends upon its functional significance.
Mutations are random and non-directional i.e. all locations in the genome have an equal probability of mutation.
However, natural selection and evolution are directional i.e. Natural selection selects only desired alleles and eliminates deleterious alleles.

For example, if a protein is highly essential for survival, its sequence is found to be highly conserved. However, it does not mean that mutations are not occurring at the locus. However, those mutations are eliminated from the population.

A mutation's geographical distribution depends upon the selection pressure and the extent of gene flow.
For example, HbS allele is deleterious in normal population.
However, it is common in African populations where malaria is prevalent (Heterozygote advantage)