The Human Genome Profile

Article excerpt

THE human genome refers to all the DNA and genes that characterize the human species that are stored in 23 pairs of chromosomes.

Humans possess over 3,000,000,000 DNA "base" pairs of hereditary material. The total number of genes in humans has been estimated at 40,000 to 60,000. The biological information encoded in these genes serves as a blueprint or software that provides a set of instructions for synthesizing the proteins in the cell at the correct time, in the correct place, and in the right quantity. The kind of protein that is synthesized is determined by the sequence and length of the two nitrogen-bearing base pairs designated by biochemical letters AT and CG along the DNA helix. Proteins perform most of life's functions and make up the majority of cellular structures. They are large and complex molecules made up of smaller repeating subunits called amino acids. There are 20 different amino acids that genes can synthesize to form the kinds of protein that cells require.

The Human Genome Project (HGP)

The HGP was conceived to sequence the 3,000,000,000 DNA bases or nucleotides in order to establish the identity and specific location of all human genes. It was an international 13-year effort that was formally launched in 1990 and completed in 2003 at a cost of more than US$3 billion. Francis Collins, who was the Director of the US National Human Genome Research Institute since 1993, headed a multinational team of 2,400 scientists who co-mapped the entire genetic blueprint.

The method used in DNA sequencing relied on the technology pioneered by Fred Sanger, the Nobel Prize winner who first synthesized the insulin gene. Though highly reliable, the Sanger method was meticulously time-consuming and expensive to undertake. A new generation of sequencing machines is now available that can do the work at unprecedented speed and low cost. J. Craig Venter, a former physiologist of the US National Institute of Health and who was actively involved in the human genome project, is the proponent of the high-speed approach to DNA sequencing in collaboration with private equipment manufacturers like Roche Diagnostics. With the earlier-generation sequencing machines, Craig Venter's genome was subjected to analysis at a cost of only $70 million and completed in just a few years. With the rapid-sequencing technology using the 454 Life Sciences Genome Analyzer, it took just two months for a handful of scientists to sequence the DNA of James Watson and at a cost of less than $1 million. The goal is to reduce the cost of sequencing further to just a few thousand dollars and make it readily affordable.

A parallel development in the genetic revolution is the invention of the "gene copying machine" which undertakes a "polymerase chain reaction" (PCR) analysis of genes. Specific target DNA sequences corresponding to genes or fragments of genes are copied or amplified over a million times in a simple enzyme reaction involving nucleotide primers, the four bases, and the polymerase enzyme. The PCR is used extensively in the study and manipulation of genes. It has many applications throughout biology and medicine and has made important contributions to the study of inherited diseases. Other applications are in forensic science and biotechnology.

Startling revelations about the human genome

With better understanding of the functioning of genes and the profile of the human genome, some startling facts have been uncovered.

1. Though the human genomic content is extremely large, the functional genes that are involved in hereditary transmission comprise only about two percent of the genome. The remainder or 98 percent consists of noncoding regions constituted by elements known as tandem or interspersed repeats (or satellite DNA), pseudogenes, and other large chunks of DNA. Much of these noncoding sequences are relics of the evolutionary past but conserved within the human species. …