1. Diagnosis with PCR This is a preparation of DNA. We zoomed in a portion of a gene. We know that two primers, Forward and Reverse, will hybridize at specific places in this exon. During a PCR reaction, a fragment of definite size will be amplified.

2. The same gene exists in another individual in the same species. It might present a mutation in this exon. The two primers, Forward and Reverse, have been chosen so that they amplify a fragment of the same size in the mutated gene. The mutation is not in the target sequence of the primers. Diagnosis with PCR

3. The primer W (Wild-type), has a target sequence which would contain the mutation in the mutated gene. A primer M (Mutant) designed to recognise the mutation would not hybridize. After PCR with the four primers, we obtain two fragments: one amplified between F and R and one amplified between W and R. invisibl e

4. Diagnostic with PCR In the mutated gene, the primer W (Wild-type), does not hybridize. A primer M (Mutant) designed to recognise the mutation, hybridizes. After PCR with the four primers, we obtain these two fragments: one amplified between F and R, and one amplified between F and M invisible

5. Diagnostic with PCR F/F f/f F/f Lets run our samples on a gel. Homozygous normal: F/F. Homozygous for the mutation (f/f) and heterozygous (F/f). After electrophoresis, the banding patterns are characteristic.