Genetic loci that contain a variable number of tandem repeats(VNTR) could be successfully amplified from a very small amount of genomic DNA by the polymerase chain reaction(PCR) and have been applied to individual identification in forensic
field.
Forensic samples are sometimes not a sample of one individual, but mixed sample, such as blood, hairs, and vaginal fluid with sperm. Even though very small amount of sample is mixed to the large one, the small fraction of the mixture is amplified
by
PCR. But sometimes it could not be detected in electrophoresed agarose gel with ethidium bromide staining, because the PCR products of small fraction are less amount rather than that of large fraction of mixed sample and because of the limitation
of the
sensitivity of ethidium bromide staining in agarose gel.
We investigated to search the detectable limitation of the PCR products of mixed sample with various ratio, experimentally. The sample were mixed with various ratio, amplified by polymerase chain reaction, electrophoresed, and stained with
ethidium
bromide. We can detect the small fraction of mixed sample from the 50% to the 5.9% or 3.0% of blood mixture and to the 0.8% of DNA mixture. In Southern blot, we can detect the small fraction in all ratio of blood mixture, to the 0.26% which is
the
smallest ratio of mixture in this experiment.
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