How is DNA Extracted From a Sample? - Pathway Genomics
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How is DNA Extracted From a Sample?

Over the years, DNA tests have been continuously refined to the point where people, in the comforts of their own home, can provide a sample that lab technicians can use to map out a comprehensive report of their genome. Through a small sample of blood, saliva, cheek cells, or a hair follicle, you can better understand your body and its needs.

When you use a DNA test, you provide a sample, usually either blood or saliva. Once this sample arrives at the lab, technicians extract the DNA from this sample. Known as DNA extraction, this is a process by which DNA is isolated from the nucleus of cells. Along with DNA testing, DNA extraction is also used to detect bacteria or viruses in the environment.

There are a number of techniques for DNA extraction. For example, the molecular technique FISH (Fluorescence In Situ Hybridization) is used to identify and itemize particular bacterial groups, whereas sequencing is done to compare portions of or whole genomes with existing sequence in a public database.

The Five Steps for DNA Extraction

While there are DNA extraction kits available, which extract DNA from cell types, these can be expensive, so most scientists and labs develop their own method for extracting DNA. While there may be slight deviations, there are general steps labs follow to extract DNA from your sample.

Step 1: Technicians first break open the cells in your sample to release the DNA. This process is known as lysing, as lysins are used to dissolve the cells. To separate the cells in your sample, technicians will grind them and add them to a salt solution. The sodium ions in the salt, which are positively charged, help protect the phosphate groups that are found in the backbone of DNA, as they’re negatively charged. Following, a detergent, such as SDS (sodium dodecyl sulfate), is added to remove lipids in the cell membrane and nuclei. As these membranes break down, DNA is released.

Step 2: Next, DNA must be separated from proteins. This cellular debris can make it difficult to get a clean reading of DNA, so technicians strive to get as clean a sample of DNA as they can. There are a few different ways to remove cellular debris and proteins. One method for precipitating the protein is to add ammonium, sodium acetate, or another salt. By vortexing with phenol-chloroform and centrifuging, the proteins can be drawn off. Alternatively, a protein enzyme may be added to the sample to degrade any proteins.

Step 3: After technicians have a clean sample of DNA, they add ice-cold ethanol or isopropanol. While DNA is soluble in water, it isn’t soluble when salt or alcohol are present. The alcohol helps wash the sample and remove the salt that was previously added. As they stir the alcohol in the sample, a white, stringy precipitate (imagine spit in a glass of water) appears and it can be retrieved.

Step 4: Once the DNA sample is extracted, technicians will further purify and clean it. Once clean, it’s resuspended in a buffer that’s slightly alkaline, such as Tris, and is ready to use.

Step 5: Even when it’s ready to use, technicians still need to determine the quality and concentration of the DNA. For example, if not enough DNA is extracted, an additional swab may be needed. Using a spectrophotometer, technicians for an optical density reading, technicians can confirm the presence of the DNA. Alternatively, instead of an optical density reading, technicians may use gel electrophoresis to indicate the presence of DNA.

Once technicians have a clean DNA sample extracted from your swab, they can review your DNA for a number of factors. While 99.9% of DNA from two people will be identical, that 0.1% varies, and it’s what makes us unique. Known as genetic markers, these are what scientists focus on when conducting a DNA test.

DNA testing can reveal your genetic ethnicity and risk factors and potential diseases you may have inherited (or may eventually inherit) from your parents, help you lose weight and more. And as we’ve all seen on crime shows, DNA samples can also be used to aid in crime scenes and trials, as fingerprints and blood samples can be used to determine the victim and perpetrator.

At Pathway Genomics, we offer a number of DNA tests centered on your health. From understanding your dietary and exercise needs to screening for potential cancer genes, DNA testing can empower you to make informed decisions about your health. With a small sample of DNA, you can uncover a number of things about your health and body you never knew.