Unit 2: #7 Genetics: Mutations (copy)

Genetic Mutations

• Changes in DNA sequence that are caused by various mechanisms 

• Eg. radiation, chemicals, incorrect replication or random mutations 

• Can have a negative effect, no effect or a positive side effect (natural selection)

Small Scale Mutations

• Include Point Mutations 

  • Mutations of an individual base pair 

•  Examples:

  • Substitution of one base for another 

  • Insertion or deletion of a single base pair 

  • Inversion of two adjoining base pairs 

What are the four outcomes from a small scale mutation?

1. Silent Mutations

2. Missense Mutation

3. Nonsense Mutation

4. Frameshift Mutations

Silent Mutations

• Has no effect on the operation of the cell (no consequences, will remain the same even with the mutations) 

• Usually occurs in non-coding regions (introns) 

• Change in codon can still represent same amino acid, since more than one codon code for same amino acid

Missense Mutations

• Change in DNA bases alters a codon 

• This is substitution 

• Causes different amino acid to be placed in protein sequence

Nonsense Mutation

• Occurs when a change in DNA base sequence causes a stop codon to be placed instead of an amino acid codon 

• This is a substitution 

• Only part of protein before “stop” is made and fragment may be digested

• Often lethal to cell

Frameshift Mutations

• Occurs when one or more nucleotides are inserted or deleted 

• Causes the reading frame of codons to shift one direction or another 

• Causes multiple missense or nonsense effects

Frameshift Mutation → Deletion

• A frameshift occurs when one or more nucleotides are removed from the DNA sequence 

• Missing amino acids will alter the protein shape drastically

Frameshift Mutation → Insertion

• Results in a frameshift by inserting a nucleotide

• DNA read in triplets, inserting a nucleotide will modify the codons and different amino acids will be translated

Translocation

• The relocation of entire genes or groups of genes from one of the chromosome to another 

• A segment of one chromosome breaks and releases a fragment. The same occurs at another unrelated chromosome 

• The two fragments then switch places 

• Results in a fusion protein with altered function.

Inversion

• The reversal of a segment of DNA within a chromosome

• No gain or loss of genetic material, but may interrupt a gene