What Are Genes, DNA and Chromosomes?

Understanding the Basics of Genetic Disorders

Scientist examining DNA autoradiogram
Cultura Science/Rafe Swan/Riser/Getty Images

You’ve heard terms like genes, DNA, the Human Genome Project, and chromosomes. But what do these words mean exactly? Increase your genetic vocabulary so you’ll understand more about genetic disorders.

What Is DNA?

DNA (deoxyribonucleic acid) carries the genetic information in the body’s cells. DNA is made up of four similar chemicals (called bases and abbreviated A, T, C, and G) that are repeated over and over in pairs.

What Is a Gene?

A gene is a distinct portion of a cell’s DNA. Genes are coded instructions for making everything the body needs, especially proteins. Human beings have about 25,000 genes. Researchers have discovered what some of our genes do and have found some that are associated with disorders (such as cystic fibrosis or Huntington’s disease). There are, though, many genes whose functions are still unknown.

What Are Proteins?

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 the body does, such as digestion, making energy and growing.

What Are Chromosomes?

Genes are packaged in bundles called chromosomes. Humans have 23 pairs of chromosomes (for a total of 46). Of those, 1 pair is the sex chromosomes (determines whether you are male or female, plus some other body characteristics), and the other 22 pairs are autosomal chromosomes (determine the rest of the body’s makeup).

What Is 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.

What Is a Mutation?

The particular order of the pairs of As, Ts, Cs, and Gs is extremely important in the DNA.

Sometimes there is a mistake — one of the pairs gets switched, dropped, or repeated. This changes the coding for one or more genes. This is called genetic mutation. A mutation may be disease-causing or harmless.

Another way the DNA code could be changed is by errors in the 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 occurs then changes (mutations) happen in the gene coding. Sometimes there may be 3 or more copies of a chromosome, or only one chromosome, instead of the normal pair.


Burton, Jess, & Jon Turney. The Rough Guide to Genes & Cloning. London: Rough Guide Ltd, 2007.

"What Is a Gene?" Understanding Genetics. The Tech Museum of Innovation. 21 Jan 2008.

"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.

Continue Reading