| Substitution of bases | - A nucleotide is replaced by another nucleotide that has a different base
- Can form stop codon
- So production of the polypeptide would be stopped prematurely
- Final protein different, not perform its normal function
- Forms codon for a different amino acid, structure of polypeptide different, different shape + not function properly
- Forms different codon but for the same amino acid, genetic code is degenerate, has no effect |
| Deletion of bases | - Causes frame shift
- Most triplets will be different, amino acids different too
- Polypetides different, nonfunctional protein, could alter phenotype
- One deleted base at the very start of a sequence could alter every triplet in the sequence
- A deleted base near the end of the sequence is likely to have a smaller impact but can still have consequences |
| Other types of gene mutation | - Addition of bases
- Duplication of bases
- Inversion of bases
- Translocation of bases |
| Addition of bases | - An extra base becomes inserted in the sequence
- Usually causes frame shift (right) + the whole sequence of triplets becomes altered |
| Duplication of bases | - One or more bases are repeated. This produces a frame shift to the right.
CGG AAA AAA CGC |
| Inversion of bases | - A group of bases become separated from the DNA sequence and rejoin at the same position but in the inverse order (back to front)
- The base sequence of this portion is therefore reversed and effects the amino acid sequence that results |
| Translocation of bases | - A group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome
- Often have significant effects on gene expression leading to an abnormal phenotype e.g. dev. of certain forms of cancer and also reduced fertility |
