Rare Diseases Genetic Disorders Overview of Genes, DNA, and Chromosomes Knowing the basics of genetics can help understand disorders By Mary Kugler, RN Mary Kugler, RN, is a pediatric nurse whose specialty is caring for children with long-term or severe medical problems. Learn about our editorial process Mary Kugler, RN Medically reviewed by Medically reviewed by Rochelle Collins, DO on May 05, 2020 linkedin Rochelle Collins, DO, is board-certified in family medicine. She is an assistant clinical professor of family medicine at Quinnipiac University and works in private practice in Hartford, Connecticut. Learn about our Medical Review Board Rochelle Collins, DO on May 05, 2020 Print The science community's knowledge of genetics increases every day, making medical discoveries and treatments more likely with each passing day. If you or someone you love has been diagnosed with a genetic condition, you may be finding it difficult to keep up with all of these genetics-based terms. Here are some of the most common terms and what you need to know about them. Andrew Brookes / Getty Images What Is DNA? DNA (deoxyribonucleic acid) carries the genetic information in your body’s cells. DNA is made up of four similar chemicals—adenine, thymine, cytosine, and guanine—which are called bases and abbreviated as A, T, C, and G. These bases are repeated over and over in pairs to make up your DNA. What Is a Gene? A gene is a distinct portion of your cell’s DNA. Genes are coded instructions for making everything your body needs, especially proteins. You have about 25,000 genes. Researchers have yet to determine what that majority of our genes do, however, some of our genes can be associated with disorders such as cystic fibrosis or Huntington’s disease. Proteins: Our Building Blocks Proteins are chains of chemical building blocks called amino acids. A protein could contain just a few amino acids in its chain or it could have several thousand. Proteins form the basis for most of what your body does such as digestion, making energy, and growing. The Basics of Chromosomes Genes are packaged in bundles called chromosomes. Humans have 23 pairs of chromosomes, resulting in 46 individual chromosomes. Of those pairs, one pair, the x and y chromosome, determines whether you are male or female, plus some other body characteristics. Females have an XX pair of chromosomes while men have a pair of XY chromosomes. The other 22 pairs are autosomal chromosomes, which determine the rest of your body’s makeup. The Human Genome The human genome is a complete copy of the entire set of human gene instructions. The Human Genome Project, completed in 2003, identified all the human genes in DNA and stored the information in databases so all researchers everywhere could use it. Understanding Mutations The particular order of the pairs of As, Ts, Cs, and Gs is extremely important in your DNA. Sometimes there is a mistake—one of the pairs gets switched, dropped, or repeated. This changes the coding for one or more genes and is called a genetic mutation. Some mutations are harmless, while other mutations can cause diseases or lead to nonviable pregnancies. Another way your DNA code could be changed is by errors in your chromosomes. Parts of a chromosome could break off, switch with part of another chromosome, or be swapped within the same chromosome. If any of these or other mistakes occur then changes, also known as mutations, happen within the coding of your genes. You can also have three copies of a chromosome, known as a trisomy, or only one chromosome, instead of the normal pair. Down syndrome, also called trisomy 21, occurs when there are three copies of chromosome 21. Was this page helpful? Thanks for your feedback! Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. "How Genetic Disorders Are Inherited." Howard Hughes Medical Institute. 21 Jan 2008. "The Basics And Beyond." Learn.Genetics. The University of Utah. 21 Jan 2008. "What Is a Gene?" Understanding Genetics. The Tech Museum of Innovation. 21 Jan 2008. Burton, Jess, & Jon Turney. The Rough Guide to Genes & Cloning. London: Rough Guide Ltd, 2007.