Advocacy in Genetics: A Teaching Guide and Workbook
The Human Genome Project
The Human Genome Project And The Genetics Behind The Project: What Does It All Mean?
For all the diversity of the world's five and a half billion people, full of creativity and contradictions, the machinery of every human mind and body is built and run with fewer than 100,000 kinds of protein molecules. And for each of these proteins, we can imagine a single corresponding gene (though there is some redundancy) whose job it is to ensure an adequate and timely supply of information. In a material sense, then, all of the subtlety of our species, all of our art and science, is ultimately accounted for by a surprisingly small set of discrete genetic instructions. More surprising still, the differences between two unrelated individuals, between the man next door and Mozart, may reflect a minute difference in their genomic "recipes". We are far more alike than we are different. At the same time, there is room for near-infinite variety. It is no overstatement to say that decoding our 30,000 genes is an enormous step toward unraveling the mysteries of life.
The complete set of instructions for making an organism is called a genome. The genome contains the blueprint for all cellular structures and activities for the lifetime of the organism. The human genome is, therefore, the full collection of genes needed to produce a functioning human being.
The Human Genome Project (HGP) is a collaborative effort of the United States Department of Energy (DOE)’s Human Genome Program and the National Institutes of Health (NIH)’s National Center for Human Genome Research. The goal of the project is to identify the function of the approximately 30,000 human genes and determine the sequence of the 3 billion DNA subunits, or bases. Research on the HGP is conducted at hundreds of university and laboratory sites throughout the United States, funded by grants from DOE and NIH. At least 18 other countries in North and South America, Europe, and Asia are doing research on the human genome, as well. The Human Genome Organization (HUGO) coordinates international efforts on human genome research.
This massive effort will provide scientists with precise information that will be key to understanding the organization and function of DNA in chromosomes. The knowledge gained and therapies developed as a result of this effort will revolutionize future biological explorations – in some ways that we can anticipate and in others that will surprise us.
Genetics: The Basics
The human genome is the full complement of genetic material in a human cell. (Despite five and a half billion variations on a theme, the differences from one genome to the next are minute; hence, we hear about the human genome -- as if there were only one.) The genome, in turn, is distributed among 23 sets of chromosomes, which, in each of us, have been replicated and re-replicated since the fusion of sperm and egg that marked our conception. The source of our personal uniqueness, our full genome, is therefore preserved in each of our body's several trillion cells. At a more basic level, the genome is DNA, deoxyribonucleic acid, a natural polymer built up of repeating nucleotides, each consisting of a simple sugar, a phosphate group, and one of four nitrogenous bases. In the chromosomes, two DNA strands are twisted together into an entwined spiral -- the famous double helix -- held together by weak bonds between complementary bases, adenine (A) in one strand to thymine (T) in the other, and cytosine to guanine (C-G). In the language of molecular genetics, each of these linkages constitutes a base pair. All told, if we count only one of each pair of chromosomes, the human genome comprises about three billion base pairs.
If unwound and tied together, all of the DNA in the human body would stretch more than 6 feet, but would be only 50 trillionths of an inch wide. For every organism – from the simplest bacteria to exceedingly complex human beings – the components of these slender threads encode all of the information necessary for building and maintaining life.
Chromosomes
The three billion base pairs in the human genome are organized into distinct, physically separate microscopic units called chromosomes. All genes are arranged linearly along the chromosomes. The nucleus of most human cells contains two sets of chromosomes, one set from each parent. Each of these sets is comprised of 23 single chromosomes – 22 "autosomes" and an "X’ or "Y" sex chromosome. (Females have a pair of X chromosomes, males an X and a Y.)
Chromosomes, when stained with dye, can be seen under a light microscope. The dye reveals a pattern of light and dark bands that indicates the variations in the amount of A and T vs. C and G. This distinctive patterning allows chromosomes to be distinguished from one another with an analysis called a "karyotype." Some chromosomal abnormalities – missing chromosomes, extra chromosomes, breaks and rejoinings called translocations – can be detected by microscopic evaluation. For example, Down syndrome, which occurs when an individual’s cells contain a third copy of chromosome 21 ("trisomy 21") is diagnosed by karyotype analysis.
Many other DNA changes are too subtle to be detected by this technique (i.e., to be seen on the chromosome) and require a different type of analysis. These subtle abnormalities, or "mutations," are responsible for many inherited conditions, such as cystic fibrosis and sickle cell anemia, or may predispose an individual to cancer, certain psychiatric illnesses, and other conditions.
Most of the information in this section is taken from To Know Ourselves.
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