Forensic Scientists usually classify individuals DNA by DNA profiling/DNA fingerprinting.The DNA isolated from biological evidence is routinely amplified by Polymerase chain reaction using short tandem repeats (STR’s) which require ~ 1 nanogram of the template DNA. However there are many samples which contain degraded DNA, or is contaminated from multiple donors as a result of which allele drop in, allele drop out, heterozygote peak imbalances are determined after PCR. Hence the resulting STR profiles are difficult to illustrate.
Due to these imbalances many forensic laboratories have initiated the use of mini STR kits for the amplification of low copy number, degraded DNA however 0.5 nanogram of input DNA is still a requirement observed here.
Some avoid the PCR process and its correspondent stochastic variation by implementing the technique of single molecule that examine each DNA molecule individually in a sample. A case study used the single molecule technique recently to do so, an amino modified DNA probe(complete amount of STR repeats at a purticular locus) was attached to a surface to which complement was added and labelling of the double stranded DNA with flourescent marker was done.
Alternately an amino modified intercalator is tethered to the surface, followed by STR repeat and its complement. In both the cases, the sample is genotyped by measuring the intensity of the fluorescence, which is proportional to the number of STR repeats present. Though this methodology is more time consuming and expensive than traditional PCR analysis but it enables generation of an STR profile in high value cases, even where the DNA evidence is limited or compromised.Tags: DNA Profiling, Heterozygote, methodology