Genotyping using spike-in control DNA to distinguish common homozygotes from rare homozygotes. A. The melting curves of AG heterozygotes (in red) are distinguished from homozygous AA (in grey). Homozygous GG samples (in blue) are not distinguished from the common AA homozygous samples.B After spike-in of a homozygous AA sample, the GG samples are converted into AG heterozygotes (in blue), and they are now distinguished from AA samples.
Garritano et al. BMC Genetics 2009 10:5 doi:10.1186/1471-2156-10-5