DNA 101: A Primer on the Science of Non-invasive Prenatal Testing

Today, most people are familiar with DNA and the impact that it can have on a person, including their looks, their health outcomes, and even their personality. The way that DNA affects humans has become increasingly important in the practice of medicine today, but it’s also become an entire market on its own. Commercial DNA testing and non-invasive prenatal testing (NIPT) have now become commonplace for people looking to better understand their risk of developing a health condition or the risk that their unborn child will develop one.

But how does DNA work and how do we test for DNA mutations? DNA is usually taught in the classroom in high school biology (around 9th or 10th grade), so it’s likely that most of us need a small refresher to brush up on their knowledge about DNA and the human genome.

What is DNA?

DNA, or deoxyribonucleic acid, is a material that holds the instructions for how your cells go about making other cells, proteins, and molecules. Without DNA, your body would not perform the functions necessary to sustain life.

This material is unique to every person. Each person’s set of DNA’s first created at conception when the sperm fertilizes the egg and the 23 chromosomes from each parent combine to create the child’s unique 46 total chromosomes.

Where is DNA found?

DNA is found in the nuclei of human cells, within structures called chromosomes. To undergo DNA testing (testing for an adult) or non-invasive prenatal DNA testing (for a fetus), the person or expectant mother undergoing testing will have their blood drawn and analyzed for particular DNA sequences and mutations. While a pregnant woman does not have her child’s cells in her bloodstream, detectable DNA fragments of the fetus are usually present in the mother’s blood sample. Lab technicians use these fragments to analyze the unborn child’s DNA for particular mutations or abnormalities. At the same time, they are also usually able to tell the sex of the baby.

What is DNA made of?

DNA consists of many smaller molecules, or nucleotides, that combine to form a “chain” of DNA. Each nucleotide is composed of deoxyribose (sugar), a nitrogenous base, and a phosphate group. The DNA chain is composed of two strands of nucleotides, held together by the bonding of their corresponding nitrogenous bases.

There are four different kinds of nitrogenous bases: adenine, thymine, cytosine, and guanine. Each of these bases has a corresponding, or opposite, nitrogenous base that it is exclusively able to bond with. Adenine nucleotides will only bond with thymine nucleotides, and cytosine nucleotides will only bond with guanine nucleotides. When the two strands of nucleotides bond, they create the two-stranded double helix DNA structure that we’re used to seeing in illustrations.

Mutations in DNA

The order of the nucleotides and their bases is a code that provides instructions to cells for how to make certain proteins and how to express certain genes. Depending on what instructions are encoded in the DNA, you will have certain genes turned “on” (or expressed) and other genes turned “off” (or not expressed).

Most mutations in DNA occur during meiosis, when a cell is dividing and needs to make a copy of its DNA for the new cell. Mutations can also occur due to damage from environmental factors. There are many different kinds of genetic mutations that can vary greatly in their expression and overall effect on a person. Depending on the mutation and subsequent expression of a gene, you or your unborn baby may be more likely to develop a particular genetic disorder or health condition later in life.

Learn More About DNA Testing

If you’re interested in learning more about genetic mutations, genetic diseases, or DNA testing in general, speak with your doctor. They will be able to recommend genetic testing that is specific to your health and family history (if deemed necessary) or refer you to a healthcare professional called a genetic counselor who specializes in the assessment and treatment of genetic health issues.


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