Give an overview of the human genome project with some relevant examples.
In order to understand the genetic revolution that is now underway, it will be helpful to provide a brief overview ofhuman genetics and the federally funded research endeavor called the Human Genome Project. DNA is found in bacteria, in nuclei of eukaryotic cells, and in mitochondria. It is made up of two extremely long nucleotide chains containing the bases adenine (A), guanine (G), thymine (Y), and cytosine (C). The chains are bound together by hydrogen bonding between the bases, with adenine bonding to thymine and guanine to cytosine. An indication of the complexity of the molecule is the fact that the DNA in the human haploid genome (the total genetic message) is made up of 3×109 base pairs.
DNA is the component of the chromosomes that carry the “genetic message,” the blueprint for all heritable characteristics of the cell and its descendants. Each chromosome contains a segment of the DNA double helix. The genetic message is encoded by the sequence of purine and pyrimidine bases in the nucleotide chains.
An individual’s heredity is determined by the DNA that is provided through the mother’s egg and the father’s sperm. The egg and sperm each contain DNA packaged in 23 chromosomes. A new embryo, made up of the DNA from the combined egg and sperm, therefore contains forty-six chromosomes in each of its cells. These forty-six chromosomes contain the entire human genetic code, called the human “genome.” As the embryo grows and develops into a fetus and into an infant, each of the body’s cells retains a copy of the 46 chromosomes.
The sequence of base pairs carries the genetic information contained within the DNA molecule. There are three billion base pairs in the human genome. The biologic machinery of the cell translates a certain sequence of base pairs into a sequence of another set of molecules called RNA. RNA, in turn, is translated into a sequence of amino acids, which are the building blocks of proteins. Through this mechanism, a specific sequence of DNA will produce, or “code for,” a specific protein. Proteins do the yeoman’s work for the cell by providing the raw materials for cellular structures and by creating enzymes that facilitate the tens of thousands of chemical reactions that are essential to life. Since DNA controls the type, amount, and sequence of proteins produced in a cell, it earns the title of “mastermolecule” or “blueprint for life.”
In the 1980s, it was becoming increasingly apparent to many scientists that an understanding of basic biology would be greatly enhanced if the detailed structure of DNA was understood. In addition, technology was emerging that gave scientists confidence that such a massive undertaking could be successful. The debate in the scientific community over whether to pursue this goal led to key reports in 1988 by the National Research Council of the National Academy of Sciences and the Congressional Office of Technology Assessment. Both supported the idea, and, despite a few voices of concern in the scientific community, Congress allocated funding for the creation of what became known as the Human Genome Project.
The goal of the Human Genome Project is to “map” and “sequence” the entire human genome. The concept of sequencing is the more straightforward, although the more difficult from a technical standpoint. As noted above, DNA is composed of a long sequence of base pair molecules linked to a helical backbone. The goal of sequencing the genome is to identify, in the proper order, the three billion base pairs that make up human DNA. Through the process of compiling this information, the telltale sequences that signify genes can be located and the exact sequences of all the genes revealed. So the process of sequencing will provide the real information that will be useful—the location and base-pair structure of all of the genes that code for humans.
The basic idea of a genome map is that it establishes landmarks throughout the genome that can be used as reference points to locate genes in their vicinity. These genetic landmarks are unique sequences of DNA that can be identified by the use of genetic tests called “probes.” A map is created by identifying sequences, called “markers,” that are positioned along each of the forty-six chromosomes. Once a map has been constructed, each gene on a chromosome can be located in terms of its position relative to a marker.
Knowledge about the effects of DNA variations among individuals through the Human Genome Project can lead to revolutionary new ways to diagnose, treat, and someday prevent the thousands of disorders that affect us. Besides providing clues to understanding human biology, learning about nonhuman organisms’ DNA sequences can lead to an understanding of their natural capabilities that can be applied toward solving challenges in health care, agriculture, energy production, environmental remediation, and carbon sequestration.