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Mapping Public Policy for Genetic Technologies

Chapter 2. What Is Genetics?

The Study of Genes, Gene Function and Families Genetics is the study of genes, gene function, and the pattern of their inheritance. DNA is the molecular code that carries inherited information from generation to generation. A gene is a segment of DNA that carries the instruction for a single protein. Genes are individual instructions for producing parts of living organisms. These instructions are passed from parent to child, and from cell to cell. Genetics is the study of genes--individual genes, in most cases. How is the gene inherited? What are its effects? How does it show up in the people who inherit one copy? Two copies? Where is the gene located? How is regulated and how is it turned on and off? What protein does it make? What does that protein do in the body? Genomics--the study of all the tens of thousands of genes carried by an organism-was born in the 1990s. Advances in gene sequencing, molecular biology and computer technology have accelerated discovery to a rate that dwarfs previous research. Researchers report finding new genes weekly or daily. The problem no longer is how to uncover new information, but how to make sense of the flood of information that threatens to engulf us.

How Information Translates into Life

DNA is the ladder-like chain of nucleic acids, the double helix formed from just four basic nucleotide building blocks: adenine, cytosine, guanine and thymine (usually abbreviated by their first letters: A, C, G and T).

These units-called bases-pair up to make the rungs of the DNA ladder: adenine always pairs with thymine (A-T); cytosine always pairs with guanine (C-G). Thus, one side of the ladder always forms a complement of the other. Each complimentary rung is called a base-pair.

Instructions written in this four-letter DNA alphabet tell the cell how to make (or express) a particular protein.

Proteins, long chains of amino acids, are the cell's main structural and metabolic components-the bricks, mortar, gears and motors of life.

A gene is the stretch of DNA that contains the instruction for a single protein. The exact succession of DNA bases that translates into a given protein is called the gene sequence.

Genes are strung together on chromosomes-tremendously long molecules of DNA tightly coiled to fit inside the cell. Human beings have 80,000 to 100,000 genes. Each human cell contains about 3 billion base pairs of nuclear DNA-a rich volume 3,billion characters long. Stretched out, the DNA in a single cell of one person would measure about 6 feet. Written on sheets of paper like this, this information would fill 2 million pages and make a stack about 650 feet high.

All together, these 3 billion base pairs of DNA make up the human genome-the entire complement of genes and regulatory structures that characterize an individual or a species.

The cell behaves like a large, diversified manufacturing company with a strong central planning and design function.

The company varies its product mix according to marketing data received at its headquarters. The headquarters staff has files packed with detailed plans for the company's products. When they decide that the company needs to change the product to respond to changing times, they delve into the files, select a plan, photocopy it, and send it by courier to one of the company's far-flung manufacturing plants.

The factory receives the plans and produces the required product.

In the cell, the nucleus functions as the corporate headquarters. The genes are the files of product plans. The messenger RNA (mRNA) is the courier packet that carries the plans. The ribosomes are the factories.

If the effect is apparent, it usually appears as a disease. In general, when people say "the cystic fibrosis gene is responsible for cystic fibrosis," they are using shorthand. A more accurate statement would be that "Damage to the gene for the cystic fibrosis transmembrane region (CFTR) protein prevents the body from producing the molecular pump that moves chloride ions in and out of the cell; when this protein malfunctions, the result is cystic fibrosis."

It is an oddity of scientific naming that most genes are named for what they do not do. Thus, a properly functioning "cystic fibrosis gene" (CFTR) keeps people from developing cystic fibrosis. A properly functioning "breast cancer gene" (BRCA1 or BRCA2) helps protect against developing breast cancer. A properly functioning "muscular dystrophy gene" keeps the muscles functioning properly. The list goes on and on.

To Next Section: Chapter 3. What is Genomics?
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