How DNA Testing Works


DNA testing is a tool that is used for identification and has various practical applications.

Common uses for DNA testing include:

  • Establishing whether or not someone is a child’s biological parent.

  • Helping to identify suspects or victims in a criminal investigation.

  • Gene therapy to test parenty or unborn babies for genetic conditions or birth defects.

  • To find out more about somebody’s genealogy.

What Exactly is DNA?

Molecule DNA is the heart of DNA testing. It is what carries out a genetic code and determines traits from personalities to eye color. Every cell in our bodies contains a complete set of our DNA including heart, skin, blood, and bones.

What Does The Test Look For?

99.9% of the DNA from two individuals will be identical. It’s that 0.1% of DNA code sequences that make us unique. These sequences are known as genetic markers. They are part of the code that is used by forensic scientists when they do a DNA test.

Identical twins will be the only people who have identical genetic markers.

However, the more closely two people are related, the more likely it is that some of their genetic markers will be similar.

The key to this kind of testing is knowing where to look in the billions of letters of genetic code in order to find those genetic markers that will identify the important differences or similarities between biological samples.

Because all the cells in the body contain the same DNA, samples can be taken from just about anywhere on the body including skin, hair, blood, follicles, and other bodily fluids.

When it comes to an attack victim, a forensic scientist may be asked to compare the DNA from skin cells found underneath the fingernails with DNA from a blood sample taken from a possible suspect.

The DNA is first isolated from the cells and millions of copies are made, using a method known as “polymerase chain reaction’, or PCR. PCR uses a natural enzyme to copy a specific stretch of DNA multiple times. Having a lot of DNA makes the genetic code simpler to analyze.

Then, the DNA molecules are split at a specific location to separate them into chunks and the code at those points are analyzed to create a DNA fingerprint. The prints from two samples are then compared to see if they match.

How Accurate Are These Tests?

There are some big implications when it comes to the accuracy of the DNA tests in Ottawa. DNA tests are sometimes the only evidence there is to prove a suspect was involved in a crime or to free somebody who has been wrongly convicted.

It is easy to tell if DNA from two samples that are biological doesn’t match. However, a match does not make you completely certain that the two samples come from the same person. There is always the chance that two individuals genetic markers could be the same, especially if they are relatives.

To reduce the risk of error, scientists test more than one marker. The more identical markers there are in two samples, the more accurate the test is going to be. However, DNA testing more markers take more time and cost more. Usually, forensic DNA tests will examine six to ten markers. The chances that two people who are unrelated have identical profiles is less than one in one billion.


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