376

28

Forensic Investigation

of population-specific STR allele frequency databases, which allow random match

possibilities to be calculated, in order to determine the significance of any match

between a sample and an entry in the suspect database.

In summary, the procedure is: collect samples, amplify selected portions using

PCR, separate and quantify lengths using capillary electrophoresis, compare with

databases, and ascertain best fits (if any). The whole procedure has been largely

automated and may take as little as a few hours. Nevertheless, DNA forensics is

estimated to contribute to a criminal justice outcome in less than 1% of recorded

crimes in England and Wales, which pioneered the technology. ⁶

The latest development in DNA forensics is to use coding sequences (selected via

appropriate PCR primers) in order to make phenotypic predictions, which may be

useful in finding suspects not in the database. Clues to biogeographical ancestry can

also be obtained. Methylation profiles of crime scene DNA can be useful to give an

indication of the age of a perpetrator.

28.2

Tracing Genetically Modified Ingredients in Food

Progress in the technical capabilities of plant biotechnology has resulted in the devel-

opment of many transgenic plants, including many comestible ones. The motivation

for introducing new genes has two primary aims: to confer resistance to pests, leading

to the diminished use of chemical pesticides; and to confer resistance to herbicides,

allowing their expanded and indiscriminate use to eliminate weeds without harming

the crops. Other aims are to enhance resistance to adverse environmental conditions

and to incorporate specific nutrients (e.g., vitamins) into plants that would not oth-

erwise be considered a source for them in the human diet. In all the above cases the

plants are destined for human consumption, which has given rise to some concerns

about their safety. (Other uses of plant genetic engineering, such as the industrial

production of drugs, are not controversial.) There is not space here to delve into the

controversies regarding the comestibility of genetically modified organisms (GMO);

whatever the merits of the arguments on both sides, there is widespread legislative

regulation of the production and distribution of GMO and the labeling of foodstuffs

containing them. Hence there is a permanent requirement for efficient and reliable

methods of detecting them.

Since, by definition, GMO contain uniquely characteristic DNA sequences, their

analysis is the most reliable and specific method for identifying GMO and this is,

indeed, the most widespread method in use. Typically the genetic material is ini-

tially screened qualitatively, following which any samples positively identified as

originating from GMO are subjected to quantitative analysis. ⁷

6 Amankwaa and McCartney (2021).

7 Kutateladze et al. (2009).