Consequences of Base Substitutions
- Imagine reading a sentence where a single letter is changed: "The dog ate the pie" becomes "The dog ate the pig."
- The meaning shifts, but the overall structure remains intact.
- Similarly, base substitutions in DNA can alter genetic instructions, with effects ranging from negligible to life-altering.
Definition
Base substitution
A base substitution is a gene mutation where one nucleotide in the DNA sequence is replaced by another.
Single-Nucleotide Polymorphisms (SNPs): Variations in the Genetic Code
- Single-nucleotide polymorphisms (SNPs) are the most common type of genetic variation in humans.
- They occur when a single nucleotide in the DNA sequence is altered.
- SNPs can be found in both coding and non-coding regions of the genome.
The genetic code is like a safety net: its redundancy helps protect against mutations.
Types of Base Substitution Mutations
1. Same-Sense Mutations
- These mutations change one codon into another that codes for the same amino acid.
- Because of the degeneracy of the genetic code, they have no effect on the protein.
- Don’t confuse mis-senseand nonsense mutations.
- Mis-sense mutations change one amino acid, while nonsense mutations create a stop codon.
A mutation changing CAG (glutamine) to TAG (stop codon) would truncate the protein.
Consequences of Base Substitutions
1. Neutral Mutations
- Many base substitutions have no effect on the organism,
- Especially if they occur in non-coding regions or result in same-sense mutations.
