Every cell of the human body contains its own instruction manual called DNA. Except for identical twins, each person has unique DNA because we receive half from our father and half from out mother—this amounts to over 8 trillion possible combinations. Small sections of a DNA strand, called a single locus probe, can be used by scientists to make a fingerprint specific to only one person out of several hundred trillion people.
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A strand of DNA has four basic components: Guanine (G), Cytosine (C), Thymine (T), and Adenine (A) are strung together as A-T, T-A, C-G, or G-C pairs called nucleotide base pairs. Each DNA strand contains millions of base pairs. Scientists use a small section of those base pairs, called a single locus probe (SNP), to discover, diagnose and identify characteristics about a person that makes them unique.
Genomes contain all of the genetic information possessed by an organism. Humans have two genomes, one passed to the child from the mother and one passed to a child from the father. Fathers pass the Y-chromosome to sons and an X-chromosome to daughters. Together, the two contributed genomes create a new genome specific to the child.
Single Locus DNA Fingerprints
A single locus DNA fingerprint is a base pair pattern, an SNP, that occurs only once in a genome. Scientists match the SNP to the same pattern in an individual’s genome. The probe itself may not have any importance other than it is only found once in the genome, but it can contain a gene or occur at certain spots in the genome, such as near a gene for a specific disease. The importance lies in what it locates.
SNP’s identify the location of a certain physical property within an organism, such as a gene or a single-point mutation. It may show the susceptibility to certain diseases or a predisposition to an illness such as cancer or diabetes. Scientists use SNP fingerprints like a map to find defects in a genome or to identify a particular individual.
SNP fingerprints have uses in genealogy, paternity and criminal investigation. With blood samples from several known relatives, scientists trace ancestry back hundreds of generations. Since children obtain half of their genome from each parent, scientists can positively identify parents of any individual. SNPs are so specific that law enforcement uses DNA to solve crimes. DNA left at a crime scene that is uncommon to the victim may positively identify the perpetrator. Many SNPs are available in databases and can be retrieved and grown in a laboratory when needed.
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