Prefectural police headquarters began this month introducing new reagents to conduct DNA profiling for criminal investigations. The National Police Agency said the new system can identify one individual among 5,650 quadrillion people, significantly improving reliability from the conventional system's one among 4.7 trillion.
DNA is a double-helix structure consisting of four types of nitrogenous bases: adenine, thymine, guanine and cytosine. The same sequence repeats in some parts of the DNA, but the number of repetitions varies from person to person.
Police have adopted a DNA profiling called Short Tandem Repeat (STR) analysis, which compares the number of repetitions for identification. The new reagents enable the DNA profiling to check 21 loci on chromosomes, increasing the number from 15 in the conventional method, thus enhancing reliability for identifying a specific base sequence.
A locus is a fixed position on a chromosome.
In addition, by upgrading the fragment analyzer, a device that analyzes DNA types, the police have become capable of conducting forensic investigations requiring only much smaller and older samples than before.
DNA testing started in Japan in 1989, and in recent years about 300,000 testings have been conducted yearly at forensic science laboratories and other facilities.
The previous system originally checked only the base sequence of chromosome 1, therefore chances of wrongly identifying an individual was one in 833 people, even combined with blood type testing. STR analysis was later introduced and improved the system's reliability by increasing the number of loci it was capable of checking to 9 in 2003 and 15 in 2006.
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