DNA (also called Deoxyribonucleic acid) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. DNA, along with the instructions it contains, is passed from adult organisms to their offspring during reproduction. Nearly every cell in a person’s body has the same DNA. We all inherit half of the DNA from our biological father and half from our biological mother. Every person’s DNA profile is unique except for identical twins.
The polymerase chain reaction (PCR) technology was invented not long after the DNA double helix structure was discovered in 1953. The PCR process sets in motion a chain reaction in which the DNA template is exponentially amplified (copied). PCR allows genetic scientists and researchers to amplify a limited amount of DNA so that billions of copies of the same DNA piece can be generated for analysis. Therefore, the PCR technology is widely used in both the DNA research and testing fields.
The genetic analyzer is an advanced capillary electrophoresis instrument that analyzes specific DNA fragments according to their lengths and generates allele size data used for human identification.
The genetic fingerprint or profile is the record of a person’s DNA markers, which are proved to be highly differential among individuals. No two persons share the same DNA profile except for identical twins. Our genetic fingerprint is inherited from our parents and is our unique biological identity.
An inclusion result for a paternity test means that the alleged father cannot be excluded as the biological father of the tested child. The probability of paternity is usually higher than 99.9% for an inclusion case, leading to the definitive conclusion that the alleged father is the biological father of the tested child.
An exclusion result for a paternity test means the alleged father is excluded as the biological father of the tested child. The probability of paternity is always 0% for an exclusion case, leading to the definitive conclusion that the alleged father is not the biological father of the tested child.
The word “Loci” is the plural form for locus, which means the location of a gene on a chromosome. Loci are also called markers to describe the specific DNA fragment used in a DNA test.
The Combined DNA Index System (CODIS) databases were established by the Federal Bureau of Investigation (FBI) to store genetic profiles of convicted felons and evidence samples with unknown origins from crime scenes for possible “hits”. CODIS utilizes computer software to automatically search the databases for matching DNA profiles. If a match is made between a sample and a stored profile, CODIS can either identify the perpetrator or link two crimes together.
STR stands for Short Tandem Repeats. It refers to a type of DNA markers that have multiple repeating short sequences. The number of repeats for these sequences is highly variable among individuals. This property of STR is used for human identification purposes.
Y-STR DNA makers are found on the male specific Y chromosome. Y-STR DNA is passed from father to son unchanged through many generations. Y-STR is not as unique as STR since all paternally related males have the same or very similar Y-STR profiles inherited from the same male ancestor.
Mitochondrial DNA (mtDNA)
Unlike STR and Y-STR DNA, both of which are nucleus DNA, Mitochondrial DNA (mtDNA) is found outside the nucleus. Both males and females inherit mtDNA from their mothers, but only females pass mtDNA to their children. mtDNA does not change very much from generation to generation. However, there is a region in the mtDNA that has a high mutation rate. When the mutation is found, it indicates that your maternal lineage has diverted from others over the years.
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