What is DNA Testing?

You’ve probably heard the term a million times in the news about criminal cases, on TV shows like CSI and Law and Order, or in high profile paternity cases or even in relation to inherited diseases and tracing your ancestry. But what is it exactly and how does it work?

First of all the DNA tests used in the above examples aren’t all the same. They all examine slightly different bits of our DNA, use different tests to it, and can tell us different things about ourselves. Click through for a easy to read summary of each of these procedures.

DNA Fingerprinting

In forensic cases, scientists usually look at about 13 different markers out of the entirety of the human DNA sequence. While this might not sound like much, the markers vary quite a lot between individuals

so the chance that you share exactly all 13 with anyone else on the planet is so small as to be nearly impossible. In practical terms however, the number of markers used by law enforcement cases can vary by state and country, due to the large cost and time needed to examine each one.

DNA Paternity testing

Testing the relationship between individuals with DNA is similar to the method for DNA fingerprinting in forensic cases. The goal however is not to find an exact match between samples but to measure how many DNA markers two or more sample share. For example the unique pattern of markers present in a child will be made from a combination of the markers present in the father and mother. As above, the odds that the marker combination in the child are due to chance rather than a pairing of the biological mother and father is statistically impossible.

DNA tests for health conditions

If you have a family history of diseases such as breast cancer or Alzheimer’s then it’s likely you’ve been tested for DNA mutations in specific genes. Currently it’s not possible to read the entire DNA sequence of individuals due to the massive size, cost and time to do so. What is possible is to examine a specific few of the 24 thousand genes that we have. This is useful since mutations in some genes such as BRCA1 have been conclusively linked to disease like breast cancer. Unfortunately screening for disease genes is only possible for conditions that have previously been identified as being caused by a mutation in a particular DNA sequence.

Ancestral DNA tests

Broadly speaking this category of tests looks for the relatedness of an individual to a historical population of people. Genealogical tests usually consist of two types, Y-Chromosome and mtDNA testing. The Y-Chromosome is carried exclusively by males and interrogating the markers within the DNA of the Y-Chromosome it is possible to trace the male ancestry. The history of the maternal line can be traced through a small piece of DNA contained within the mitochondria of all cells, and is passed down exclusively from the mother. Genealogical DNA tests generally have no medical or diagnostic value and are only useful for tracing lineages over large time scales. They are most useful when used in conjunction with genealogical records and family trees.