DNA is often called the blueprint of life, but what does that really mean? Elizabeth Worthey, Ph.D., associate professor, Department of Genetics in the Heersink School of Medicine, explains everything you need to know about genetics.
DNA, or deoxyribonucleic acid, is the genetic material found in all living organisms. It is made of long chains of chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). These chains make up chromosomes. Human chromosomes span two copies of 3.2 billion nucleotides in nearly every cell.
“Think of DNA as an instruction manual,” Worthey said. “It tells our cells how to form, operate, and interact with their surroundings.”
Most DNA is stored in the cell nucleus. A small portion is found in the mitochondria, the energy-generating structure of the cell. About 99.9% of the DNA sequence is the same in every person. The remaining 0.1% explains our unique traits.
Genes are specific sections of DNA that carry instructions for making proteins or other molecules. Proteins do much of the work in our bodies, including fighting infections, regulating the heartbeat, and helping us see.
“Some genes work like switches, deciding when, where, and how much of a protein is made,” Worthey said. “Others provide the instructions for building those proteins.”
Not all essential DNA sections are genes. Many regions help control when and where genes are active.
A genetic variant is a change in the DNA sequence. When a variant occurs in reproductive cells, it can be passed from parent to child and will be present in every cell of the body. Other variants arise later in life in specific cells. These are called somatic mutations, which are not inherited. “Somatic mutations are a major cause of cancer,” Worthey explained. “They can lead to cells growing when they should not, forming tumors, or spreading throughout the body.”
Most variants are common and have little or no effect, while others influence how cells function. “Most variants do not cause harm,” Worthey said. “But some can affect how a cell works, and a subset can lead to disease.”
Some variants can cause rare inherited conditions such as cystic fibrosis or muscular dystrophy. Others may contribute to risk of more common diseases like diabetes or heart disease, especially when combined with environmental or lifestyle factors.
In pharmacogenomics, specific genetic variants influence proteins that metabolize drugs, altering how a person responds to medication. This can affect which drug works best, how much is needed, and what side effects may occur.
Understanding a person’s DNA can help doctors predict disease risk, choose the right treatments, and in some cases prevent illness altogether.
“The more we learn about our individual genetic code,” Worthey said, “the more we can use that knowledge to improve care and personalize medicine for each individual.”