Sometimes a gene can mutate
- Rare, random change in an organism's DNA that can be inherited
- Occur continuously
Mutations mean gene is altered
- Produces a genetic variant (different form of the gene)
As genes code the sequence of amino acids that make up a protein, gene mutations can lead to changes in the protein
Most genetic variants have very little or no effect on the protein the gene codes for
- Some will change it so little that its function is unaffected - means most mutations have no effect on phenotype
Some variants have a small influence on phenotype - alter individual's characteristics but only slightly
- Some characteristics are controlled by more than one gene
- Mutation in one of the genes may change eye colour - difference may not be huge
Very occasionally, variants can have a dramatic effect that they determine phenotype
- Cystic fibrosis is caused by a mutation that has a huge effect on phenotype
- Gene codes for a protein that controls movement of salt and water into/out of cells
- However, protein produced by the mutated gene doesn't work properly - leads to excess mucus production in lungs and digestive system
If environment changes, and the new phenotype makes an individual more suited to a new environment
- Can become more common throughout species relatively quickly by natural selection

Inheritance, Variation and Evolution