What is DNA?

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The complexity of the human body is an undeniable fact. Made of as many as 100 trillion cells, each cell in the body serves an integral purpose, from protecting our internal organs to transporting oxygen throughout the body, even enabling the creation of human life during the process of reproduction. Despite the incredible diversity of cells and their various functions, each cell (with the exception of red blood cells) shares a single important trait: a nucleus. The nucleus houses genetic information that is identical from cell to cell, bundled

Since all cells contain the same genetic information, potential sources for DNA collection are extensive; small tissue samples, hair roots and saliva are just a few examples of potential sources.

Collecting DNA Samples for Paternity Testing

Genetipeda™ » Collecting DNA Samples for Paternity Testing

All DNA testing laboratories require DNA sources that are clean (free of contaminants and other DNA) and densely populated with DNA (called “high yield”). DNA customers desire simple and reliable collection methods. Past collection methods such as blood or tissue biopsies were costly and often painful or traumatic. Fortunately science has virtually eliminated the need for these types of samples in DNA paternity testing procedures.

While IDENTIGENE can extract DNA from almost any specimen type, our standard DNA Paternity Test uses the easy and non-invasive, buccal (cheek) swabs. This collection procedure involves rubbing a special polyester-tipped (not cotton) swab against the inside of the cheek. It is a non-invasive, simple way to perform collection and typically yields thousands of times the amount of “clean” DNA necessary for use in a single test.

Extracting the DNA

Genetipeda™ » Extracting DNA for Paternity Testing

There are many methods to extract DNA from cells. All methods use three basic steps:

Lyse (break open) the cells
Separate the DNA from other cell proteins and lipids
Collect the pure DNA in a stable solution.

Cell lysis is performed by introducing a detergent and protein consuming enzyme to the cells. This releases the DNA from the nucleus. After completing this step what remains is a slurry (liquid mixture) of nucleic acids (DNA), proteins and lipids.

This relatively “dirty” sample is hardly the type of sample to use in a DNA test. The DNA is separated from protein and lipids using sophisticated robotics.

The extraction robot adds the detergent and enzyme to lyse the cells, transferring the DNA mixture to tiny silica-based nano-beads (one billionth of a meter in size); the DNA sticks to the beads while the protein and lipids are washed away. Now our DNA is pure. However, it is still unusable for proper testing.

The final step to DNA extraction from cells is elution (removing the DNA from the beads).The extraction robot adds a solution which causes the DNA to release from the beads. The released DNA is collected and ready for testing.

The PCR Process: Amplifying DNA for analysis

Genetipeda™ » Amplifying DNA for analysis

So, exactly how do we get all those numbers from a cheek swab? Advances in DNA testing technology enable scientists to transform a particle of DNA into a probability of paternity.

The lab technician puts the extracted DNA into a special solution containing primers, small synthetic DNA fragments that can identify and copy the DNA markers, and enzymes, used to build copies of the DNA. PCR begins by separating the double-stranded DNA – simply by turning up the heat. As the solution cools, the primers bind to complementary regions of DNA they are designed to target. One primer contains a fluorescent dye so it will be detectable on a DNA analyzer.

By the end of the first cycle a single bit of DNA has been duplicated into two identical strands of DNA. These steps, heating and cooling the DNA solution and copying the DNA strands, are repeated 28 times to allow for billions of copies of DNA fragments to be created so that a fluorescent signal can be amplified loud enough to be viewed with a machine called a Genetic Analyzer.

Measuring DNA for Paternity Testing

Genetipeda™ » Measuring DNA for Paternity Testing

After PCR is complete, all 16 markers (loci) of interest (15 markers useful for paternity, 1 gender determining marker for verification) have been amplified into many copies. Individual variation at each marker will create different DNA fragment sizes. Sophisticated Genetic Analyzers detect the fluorescent dye in each fragment and, with the assistance of analysis software, the size of each fragment is measured. The fragments sizes are represented by the numbers (alleles) that appear on your paternity test report. The allele information from each of the 16 loci is used to determine a biological relationship between individuals.

Reading the Paternity Test Report

Genetipeda™ » Reading the Paternity Test Report

A child’s results will be a combination of 1/2 the father’s alleles and 1/2 the mother’s alleles. The child's alleles that are not seen in the mother's DNA therefore must be inherited from the biological father. If the DNA from the tested (alleged) father does not share matching alleles with the child's DNA, then the tested man is not the biological father. If the genetic material does contain matching genetic markers, then the probability that the tested person is the biological father is reported (typically greater than 99.99%).

For more information on how probability of paternity is calculated visit our page on “Understanding Your Paternity Test Report”.

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