A HUMAN CELL
Each of the 100 trillion cells in the human body (except red blood cells) contain the entire human genome — all the genetic information necessary to build a human being. This information is encoded in 6 billion base pairs, subunits of DNA. (Egg and sperm cells each contain three billion base pairs of DNA.)

THE CELL NUCLEUS
Inside the cell nucleus, 6 feet of DNA are packaged into 23 pairs of chromosomes (one chromosome in each pair coming from each parent).

A CHROMOSOME
Each of the 46 human chromosomes contains the DNA for hundreds or thousands of individual genes, the units of hereditity.

A GENE
Each gene is a segment of double stranded DNA that holds the recipe for making a specific molecule, usually protein. These recipes are spelled out in varying sequences of the four chemical bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). The bases form interlocking pairs that can fit together only one way: A pairs with T; G pairs with C.

A PROTEIN
Proteins, which are made of amino acids, are the body's workhorses — essential components of all organs and chemical activities. Their function depends on their shapes, which are determined by the estimated 40,000 genes in the cell nucleus.

Illustration: Karen Barnes, Stansbury Ronsaville Wood, Inc.