Why so many errors in our DNA?

As scientists learn to read the instructions in our genes, they are discovering that much of our DNA is riddled with errors.

Fortunately, most of the errors are harmless. Considering the difficulties involved — the 6 feet of DNA in a human cell consists of 6 billion subunits, or base pairs, coiled and tightly packed into 46 chromosomes, all of which must be duplicated every time a cell divides — our general state of health is something of a miracle.

We each inherit hundreds of genetic mutations from our parents, as they did from their forebears. In addition, the DNA in our own cells undergoes an estimated 30 new mutations during our lifetime, either through mistakes during DNA copying or cell division or, more often, because of damage from the environment. Bits of our DNA may be deleted, inserted, broken, or substituted. But most of these changes affect only the parts of DNA that do not contain a gene’s instructions, so we need not worry about them.

Problems arise only when an error in DNA alters a message that tells certain cells to manufacture a particular protein.

To stay alive and functioning, the human body requires a daily crop of billions of fresh protein molecules — about 50,000 different kinds of proteins that must be supplied in the right quantites, at the right times, and in the right places. Our cells are kept extremely busy linking together amino acids — the building blocks of proteins — in the right order to produce these diverse proteins.

An error in just one base can bring the wrong amino acid, altering the protein. Much of the recent progress in reading DNA has come from analyses of genetic errors.

©Howard Hughes Medical Institute, as published in Blazing a Genetic Trail, 1991.