OVERVIEW OF GENETICS
Hardly a week goes by without a major news story involving a genetic breakthrough. The increasing pace of genetic discoveries has become staggering.
The Human Genome Project is a case in point. This project began in the United States in 1990, when the National Institutes of Health and the Department of Energy joined forces with international partners to decipher the massive amount of information contained in our genome—the DNA found within all of our chromosomes.
Working collectively, a large group of scientists from around the world has produced a detailed series of maps that help geneticists navigate through human DNA. Remarkably, in only a decade, they determined the DNA sequence (read in the bases of A, T, G, and C) covering over 90% of the human genome.
The first draft of this sequence, published in 2001, is nearly 3 billion nucleotide base pairs in length.
The completed sequence, published in 2003, has an accuracy greater than 99.99%; fewer than one mistake was
made in every 10,000 base pairs (bp)! Studying the human genome allows us to explore fundamental details about ourselves at the molecular level.
The results of the Human Genome Project are expected to shed considerable light on basic questions, like how many genes we have, how genes direct the activities of living cells, how species evolve, how single cells develop into complex tissues, and how defective genes cause disease.
Furthermore, such understanding may lend itself to improvements in modern medicine by leading to better diagnoses of diseases and the development of new treatments for them .
As scientists have attempted to unravel the mysteries within our genes, this journey has involved the invention of many new technologies.
For example, new technologies have made it possible to produce medicines that would otherwise be difficult or impossible to make.
An example is human recombinant insulin, sold under the brand name Humulin.
This medicine is synthesized in strains of Escherichia coli bacteria that have been genetically altered by the addition of genes that encode the polypeptides that form human insulin. The bacteria are grown in a laboratory and make large amounts of human insulin.
As discussed in Chapter 19 , the insulin is purified and administered to many people with insulin dependent
DNA, the molecule of life
Trillions of cells Each cell contains:
• 46 human chromosomes, found in 23 pairs
• 2 meters of DNA
• Approximately 3 billion DNA base pairs per set of chromosomes, containing the bases A, T, G, and C
• Approximately 20,000 to 25,000 genes coding for proteins that perform most life functions