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.
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.
More easy to read summaries of each of these procedures
at
http://dnatestingguides.com
http://dnatestingguides.com 