BRAIN MAPPRING | test and Techniques
Posted Feb 2018
Posted Feb 2018
All forensic methods for individualization—fingerprints, dental impressions, striations on bullets, hair and fiber comparisons, voice spectrograms, neutron-activation analysis, blood-grouping and serum-protein and enzyme typing, as well as DNA profiling—demand an ability to match samples with reasonable accuracy with respect to characteristics that can help to differentiate one source from another. If such evidence is to be useful in court, scientifically acceptable procedures must permit the reliable measurement and comparison of physical features. Likewise, a scientific basis must exist for concluding that properly performed comparisons can distinguish possible sources.
DNA profiling (also called DNA fingerprinting, DNA testing, or DNA typing) is the process of determining an individual's DNA characteristics, called a DNA profile, that is very likely to be different in unrelated individuals, thereby being as unique to individuals as are fingerprints (hence the alternative name for the technique). DNA profiling with the aim of identifying not an individual but a species is called DNA barcoding.
DNA profiling is most commonly used as a forensic technique in criminal investigations to identify an unidentified person or whose identity needs to be confirmed, or to place a person at a crime scene or to eliminate a person from consideration. DNA profiling has also been used to help clarify paternity, in immigration disputes, in parentage testing and in genealogical research or medical research. DNA fingerprinting has also been used in the study of animal and floral populations and in the fields of zoology, botany, and agriculture
Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different that it is possible to distinguish one individual from another, unless they are monozygotic ("identical") twins. DNA profiling uses repetitive ("repeat") sequences that are highly variable, called variable number tandem repeats(VNTRs), in particular, short tandem repeats (STRs), also known as microsatellites, and minisatellites. VNTR loci are very similar between closely related individuals but are so variable that unrelated individuals are extremely unlikely to have the same VNTRs.
DNA Profiling Developed by Professor of Genetics Sir Alec Jeffreys, the process begins with a sample of an individual's DNA (typically called a "reference sample"). A common method of collecting a reference sample is the use of a buccal swab, which is easy, non-invasive and cheap. When this is not available (e.g. because a court order is needed but not obtainable) other methods may need to be used to collect a sample of blood, saliva, semen, vaginal lubrication, or other appropriate fluid or tissue from personal items (e.g. a toothbrush, razor) or from stored samples (e.g. banked sperm or biopsy tissue). Samples obtained from blood relatives (related by birth, not marriage) can provide an indication of an individual's profile, as could human remains that had been previously profiled.
A reference sample is then analyzed to create the individual's DNA profile using one of a number of techniques, discussed below. The DNA profile is then compared against another sample to determine whether there is a genetic match.
Using PCR technology, DNA analysis is widely applied to determine genetic family relationships such as paternity, maternity, siblingship and other kinships.
During conception, the father’s sperm cell and the mother’s egg cell, each containing half the amount of DNA found in other body cells, meet and fuse to form a fertilized egg, called a zygote. The zygote contains a complete set of DNA molecules, a unique combination of DNA from both parents. This zygote divides and multiplies into an embryo and later, a full human being.
At each stage of development, all the cells forming the body contain the same DNA—half from the father and half from the mother. This fact allows the relationship testing to use all types of all samples including loose cells from the cheeks collected using buccal swabs, blood or other types of samples.