DNA Testing

DNA TESTING

DNA is material that governs inheritance of eye color, hair color, stature, bone density and many other human and animal traits.  DNA is a long, but narrow string-like object.  A one foot long string or strand of DNA is normally packed into a space roughly equal to a cube 1/millionth of an inch on a side.  This is possible only because DNA is a very thin string.

Our body's cells each contain a complete sample of our DNA.  One cell is roughly equal in size to the cube described in the previous paragraph.  There are muscle cells, brain cells, liver cells, blood cells, sperm cells and others.  Basically, every part of the body is made up of these tiny cells and each contains a sample or complement of DNA identical to that of every other cell within a given person.  There are a few exceptions.  For example, our red blood cells lack DNA.  Blood itself can be typed because of the DNA contained in our white blood cells.   Not only does the human body rely on DNA but so do most living things including plants, animals and bacteria.  

A strand of DNA is made up of tiny building-blocks.  There are only four, different basic building-blocks.  Scientists usually refer to these using four letters, A,  T,  G,  and C.  These four letters are short nicknames for more complicated building-block chemical names, but actually the letters (A,T, G and C) are used much more commonly than the chemical names so the latter will not be mentioned here.  Another term for DNA's building blocks is the term, "bases."  A, T, G and C are bases. 

DNA testing is the process of using DNA to assist in the identification of individuals. While 99.9 percent of human DNA sequences are the same, scientists are able to use repeat sequences in the DNA to distinguish individuals from each other since this information is always different. DNA testing is also known as DNA profiling, DNA typing or genetic fingerprinting and can be used to link suspects to crimes, establish paternity or maternity, prove blood relationship or determine genealogical roots.

Test Background ( DNA Testing background)

                The fundamental key of DNA testing is in finding the differences in specific DNA sequences. Two sets of DNA are needed for comparison. In forensics, for example, these are often the DNA samples from the crime scene compared with the DNA from a suspect. The first step in testing may vary depending on different techniques (described in the following sections) but is basically the isolation of a part of a DNA sequence. The cut DNA fragments are then sorted by size using gel electrophoresis. A blot of the gel is made to record the gel's results and a probe is released onto the blot to find and bind onto a similar DNA sequence as the one associated with the probe.

History of DNA Testing

DNA testing is a powerful tool for identification. With today's technology, DNA tests can now identify individuals with almost 100% certainty. Identification has not always been this conclusive. Before DNA tests, the science community used other biological tools to identify people and determine relationships. These techniques, which included blood typing, serological testing, and HLA testing, were useful for other uses (such as matching blood and tissue donors with recipients and reducing the rejection rate for transplant patients), but they were not effective for identification and determining relationships.

With the introduction of DNA testing in the late 1970s and 1980s, scientists saw the powerful tool this process was for identification and determination of biological relationships. Thanks to the advent of DNA testing, Determine the identity of individuals we can now and their relatives with exceptional accruacy and conclusiveness.

1980s—DNA Testing via RFLP      
Power of Exclusion: 99.99% and higher

In the 1980s, DNA testing became available. DNA, the genetic material, is found in all cells of the body. You inherit a unique combination of DNA from your mother and father, and no two persons have the same DNA, except for identical twins. Thus, DNA can be used to conclusively determine paternity.

The Science of DNA Testing via RFLP

In RFLP (Restriction Fragment Length Polymorphism), blood samples are taken from child, mother, and alleged father. DNA is purified from the blood samples in the form of a long, stringlike molecule.The purified DNA samples are placed into a “digestion mix” with biological molecules called restriction enzymes. The enzymes cut the DNA into different-sized pieces, called fragments.

The size of each fragment depends on the type of DNA that is inherited from the mother and father. Half of the child’s fragments should match DNA fragments from the mother, and the rest should match DNA fragments from the father.

If a fragment is found that matches neither the mother’s nor the father’s DNA fragments, additional analysis is required—the mismatch might be a result of mutation. Mutations are random changes that rarely occur in DNA. Statistical analysis is used to determine the chance that a mutation has caused the mismatch. If too many fragments do not have a match, however, the alleged father is excluded.

DNA testing via RFLP is conclusive, but it is an old technique that requires larger amounts of samples and longer processing time. New developments in DNA technology have paved the way for DNA testing via PCR, discussed below. 

1990s—DNA Testing via PCR
Power of Exclusion: 99.99% and higher

The Polymerase Chain Reaction (PCR) became established in the 1990s as the standard method for paternity testing. Like RFLP, this method uses DNA, which is found in all cells of your body. You inherit a unique combination of DNA from your parents.

Because scientists have extensively used PCR for DNA testing, a greater amount of information has been accumulated to form a database for accurate DNA analysis. This large database enables paternity testing via PCR to have the highest power of exclusion.

The Science of DNA Testing via PCR

The Polymerase Chain Reaction (PCR) is a powerful method for analyzing DNA. PCR can be performed on very small amounts of biological samples, from almost every part of the body. All cells in the body have the same DNA, so the results are the same regardless of the type of sample taken.PCR allows scientists to make billions of copies of DNA from a small sample, such as a buccal swab (a cotton swab rubbed against a patient’s inner cheek). DNA is extracted from the swab as a long, stringlike molecule. PCR creates copies of only a small fragment from this molecule—scientists can control which part of the DNA molecule is copied. Once the copies are made, the DNA fragment can be easily analyzed.

In paternity testing, 16 different DNA fragments are copied at the same time. These fragments are often referred to as loci (singular locus), locations on the DNA that have been found to be useful for human identification. These fragments form the DNA profile.

The DNA profile is interpreted in a manner similar to RFLP. Half of a child’s DNA profile (8 fragments) matches fragments on the mother’s DNA profile, and the other half matches fragments on the father’s DNA profile. If a mismatch is observed, statistical analysis and additional tests will show whether or not the mismatch is a result of mutation (a rare, random change in the DNA). If too many fragments do not have a match, however, the alleged father is excluded (he is not the father).DNA Testing via PCR is the fastest, most accurate method for determining paternity.

Restriction Fragment Length Polymorphism

Restriction fragment length polymorphism (RFLP) is a technique of DNA isolation that is often used in forensics. Generally, RFLP requires large amounts of undegraded DNA, so it is ideal for crime scenes that are new with a lot of evidence. Once sufficient samples are obtained, restriction enzymes are used on the DNA to isolate a sequence known as AATT. The fragments are then run through a gel electrophoresis, made into a blot and probed (as mentioned above). The sizes of the DNA fragments found by the probe are analyzed and the results of each sample of DNA are compared. A match may be declared if the bands are all within 5 percent of one another in size.

Polymerase Chain Reaction

 Polymerase chain reaction (PCR) is another technique of DNA amplification commonly used in forensics. Unlike RFLP, PCR has the ability to use information from very small and even degraded samples by greatly amplifying specific regions of DNA. PCR uses two short pieces of DNA known as oligonucleotide primers and a thermostable DNA polymerase to isolate the region of DNA to be copied. The samples of isolated DNA are then run under gel electrophoresis and blotted just as with RFLP for analysis and comparison. It should be noted that contamination of the DNA sample is of particular importance in PCR analysis. If any type of other DNA from either other people or things such as bacteria are present, many copies of the isolated DNA fragments may be made from the wrong source and give false results.

Time Picks Best Invention Of The Year 2008: DNA Test "23andMe"

Time Magazine has announced the 50 best inventions of 2008 and at its top is a DNA test called 23andMe. It's not as well-known as the iPhone, Time's best invention of 2007, but if 23andMe catches on, it will change how much we know about ourselves, our families, and possibly, about others.

Created by Anne Wojcicki and Linda Avey, 23andMe is a mail order, self-administered DNA test! For $399, you receive a 23andMe kit containing a funnel and cap. You spit into the funnel, cap it, and return it to 23andMe's special laboratory for analysis. In four to six weeks, you will receive an email from the company, letting you know how to find your results online.
The number 23 stands for the 23 pairs of chromosomes found in the human genetic sequence. However, the actual analysis of your saliva sample is done on nearly 600,000 single nucleotide polymorphisms (SNPs), that are scattered across the genetic sequence. 23andMe also analyzes a few thousand places on the mitochondrial DNA.
23andMe, coincidentally, can provide you with you with information on your predisposition for 23 conditions that have genetic markers; however, this number is growing, as more research data is compiled for other diseases and conditions. Currently, the list of conditions includes age-related macular degeneration, Crohn's disease, Parkinson's disease, rheumatoid arthritis, resistance to HIV/AIDS, and diabetes I and II.
In addition to the known conditions with genetic predispositions, the client also has access to research on 68 other conditions being studied, but not analyzed on the DNA test. 23andMe also provides an analysis of a client's ancestry!
Ms. Wojcicki and Ms. Avey have had some famous clients so far, including Warren Buffet and Rupert Murdoch. They may be included in the funding of 23andMe, but we do know that Ms. Wojcicki's husband, Sergey Brin, co-founder of Google, has played a large role in funding the project.