Rapid individual identification by minisatellite variant repeat (MVR)-PCR at D1S8 locus using "exponential law"

We describe an efficient and simple minisatellite variant repeat mapping by PCR (MVR-PCR) method based on the assignment of the tandem array of 29 bp repeating units into a-type, t-type and 0-type (a rarely appearing unamplified unit), from the first repeat unit position (code position 0) of 293 bp in D1S8 locus. After microchip electrophoresis of PCR product amplified from the target DNA of a human hair root, each rung of the ladder at the position of 293 + 29 n bp (n: code position) was detected and the type of repeating unit was determined, i.e., aa, a0, tt, t0, at and 00. The peak area of the rungs from PCR product decreased with increase in code position. We found for the first time that the logarithmic plots of the peak area against the code position showed a linear relationship, which implied that peak areas decrease exponentially. The present method was successfully applied to identify 37 individuals using only a hair root as a biological specimen. This "exponential law" is expected to be an effective tool in forensic science.