IB Biology D1.3 Notes

Mutations

Just like the generation of new alleles, the process of evolution is often dependent on mutations. These are defined as changes in the base sequence of DNA. Most of the time they are not advantageous, but neutral, harmful, or lethal.

There are two main types of mutations you need to be aware of:

1. A substitution mutation replaces one nucleotide with one another. Due to the degeneracy of the genetic code, this may produce a codon for the same amino acid, having no effect, or produce a codon for a different amino acid.
2. A frameshift mutation refers to a mutation that shifts an entire part of the amino acid sequence by one or two nucleotides. This changes all the codons in that part, resulting in a different polypeptide.
   1. An insertion alters the DNA sequence by adding nucleotides to the gene.
   2. A deletion similarly will change the DNA sequence by removing nucleotides from the gene.