Detection of child microchimerism by QT-PCR. (A) The mother's allele, or major allele, has low cycle number corresponding to its comparatively high DNA concentration. (B) The minor allele or microchimeric cell population has a much higher cycle number because the minor DNA exists at a much lower concentration than the major allele. The method is to calculate the change in cycle threshold (ΔCT) to show the ratio of the minor population to the major population.