genetic variants and phenotype

• Mutations are rare, random changes that continuously occur in the sequence of DNA bases in a gene.
• DNA base sequence determines sequence of amino acids for a protein, so mutations sometimes lead to a change in protein the gene codes for. However, mostly it is only altered slightly so there is not change in appearance or function.
• • Insertions: A new base randomly inserted in the DNA sequence.

  • Deletions: A base is randomly deleted.

  • Substitutions: A base is randomly swapped for another.
• On rare occasions, mutations lead to the development of new alleles and so new phenotypes.
• On rare occasions, mutations significantly alter a protein and they no longer have the ability to preform their function.
• Sickle cell anaemia:

  • Mutation changes haemoglobin in a red blood cell.

  • RBC become stiff and shaped like a sickle cell.

  • They get stuck in narrow blood vessels which block blood flow.
• A mutation may affect the ability of RNA polymerase to bind to non-coding DNA which may affect protein production and phenotype.