Question

Two persons differ in several SNPs (single nucleotide polymorphisms), however, after their proteins are compared, you realize that only some SNPs induce changes in amino acid sequence. What is going on here? How come some SNPs induce amino acid change while others don't?

Answer 1

Silent mutation: these are point mutations which do not result in any observable phenotypic effect. This means the change in the nucleotide can result in the expression of a different or altered codon but produces the amino acid with similar functionality.

The substitution of a single nucleotide at a specific location in the genome is known to produce single nucleotide polymorphism(SNP). In a population every individual show a variation at s single nucleotide which give rise to this polymorphism and it is very rare that a group of individuals will have common SNP. This polymorphism usually occur in the non coding region as compared to the coding region.

The SNP present within a coding region does not necessarily result in the change in the amino acid sequence of the protein. In the coding region the SNP can be of 2types:

1. Synonymous SNP- this type of polymorphism in the single nucleotide does not result in the change in the amino acid due to the degeneracy of the genetic code i.e amino acids can be coded by more than one codon.

2. Non synonymous SNP- these are the altered nucleotide which can code for a different amino acid than expected one. So these are the SNPs which result in the change in the amino acid in the protein sequence. It can be either misense(the SNP results in the expression of a codon that codes for different amino acid) or nonsense (resulting in the premature stop codon and hence results in the formation of non functional protein).