MAPPING THE GENOME
The Blueprint of Life
… and Death
To see a World in a Grain of Sand And a Heaven in a Wild Flower, Hold Infinity in the palm of your hand And Eternity in an hour.
—William Blake Auguries of Innocence
N eatly packaged inside every cell in our bodies (except red blood cells) is a dense structure called the nucleus of the cell.We have been able to see the nucleus for as long as we have had microscopes—more than one hundred years.The discovery of the contents and purpose of the nucleus during the last century has been one of the major achievements in science—an achievement perhaps more important than discovering the law of gravity or formulating the theory of relativity.We now know that the nucleus contains DeoxyriboNucleic Acid (DNA) and the genetic code:the blueprint used to create and destroy life.In human beings, the nucleus contains between 30,000 and 40,000 genes, which are located on 23 pairs of chromosomes.(The exact number is still being debated.)
We tend to think that genes are destiny. One set of chromosomes is passed to us through our fathers and the other set through our mothers. The 23 pairs produced through this union give us hereditary traits that are sometimes viewed as creating genetic determinism. We fear that we are likely to inherit father's heart problems or alcoholism or mother's breast cancer. No one likes to feel deprived of autonomy or freedom. Because mental illnesses are among the most familial of human diseases, the possibility of genetic determinism is all the more frightening.
Fortunately, the story is not so simple—or so grim.
Here is the clue as to why. Every cell in our bodies has exactly the same DNA and the same genes.Yet these cells, built from the same genes, may be quite different from one another.We have brain cells, liver cells, kidney cells, heart cells, skin cells, stomach cells, eye cells, hair cells, and many others—all produced from the same set of instructions coded in our DNA and our genes. By some magical process, the basic blueprint of