3. Skim the text to check your ideas.

Reading C

THE GREATEST BIOLOGICAL DEVELOPMENT IN SCIENCE HISTORY

Scientists have cracked the code, the longest, tiniest imaginable, most important, oldest code: the code of human life, the DNA sequence of humanity. The numerics are staggering: written in just a four-letter alphabet (A, T, C, G), the human genome is around 3 billion letters long (or about one billion "words" in length since each word (a codon) is three letters long), and there are around 600 billion-trillion copies of it on Earth (6 billion people times 100 trillion cells per person). It took about 3 billion years to create (the age of life on Earth) and only 15 years to decipher if one starts at the beginning of the Human Genome Project. Alternatively, it might be argued that it has taken several 100,000 years (the age of Homo sapiens) for humans to look inside themselves and figure out their vital essence.      The human genome is the crown jewel of 20 years of biological research, the most important accomplishment in the field to date. On a scale unmatched in the history of biology, it has been a massive project built on the scientific endeavors of decades of dedicated investigators. In effect, biologists have climbed Mount Sinai and brought back the hitherto secret scriptures of life.

The genome encodes the proteins that form the structural elements of life and that regulate numerous biological processes. Genes provide the characteristics that distinguish one individual from another and allow these features to be passed from one generation to the next through reproduction, thereby providing the microscopic mechanism for evolution. For these reasons, the genome is often called the blueprint for life. In short, the sequence of the human genome and similar sequences for other organisms comprise the Books of Life, the Bible of Biology so to speak.

The genome is composed of chromosomes. In humans, there are 24 four different types, which are labeled chromosome 1, chromosome 2, . . ., chromosome 22, X and Y. Thus, the Great Code is contained in 24 volumes.

Humans, like other higher forms of life, are diploid (that is, their chromosomes are duplicated in the nucleus of a cell). There are 23 pairs, 22 of which are matched: There are two copies of chromosomes 1 through 22, and then either an XX pair for females or an XY pair for males. Each chromosome consists of a long DNA molecule wrapped into a compact form around proteins known as histones – roughly like the way thread is wound about a bobbin. DNA is comprised of two long chains of nucleotides bound and twisted about each other to form a helix. The nucleotides are of four types: adenine (symbol A), guanine (symbol G), cytosine (symbol C) and thymine (symbol T). Specifying the nucleotide sequence as a series of "biological letters," such as CTATGAT . . ., determines the DNA molecule.

Genes are certain sections of the DNA that code proteins. Messenger ribonucleic acid, abbreviated mRNA, transports the information in the DNA to the protein-producing machinary of a cell. In a given cell, certain genes are turned on, meaning that they are allowed to generate the proteins that they code, while other genes are switched off. The genes that are turned on determine the function of a cell.

The amino acid sequence of a protein coded by a gene is determined from the genetic code. Less than 1.5% of the genome encodes proteins; the rest consists of non-coding sequences, a sizeable fraction of which is junk, meaning that it appears to have no present biological purpose.

Feminists will be happy to learn that the male-defining Y chromosome is a junkyard, full of repetitive, non-functional nucleotide sequences. Furthermore, there are many copies of sperm-production genes in the Y chromosome; it is as though males are afraid of sterility or trying to defend themselves against female invasion. What is worse is that evolution has reduced it to a little stump in comparison with the other chromosomes and that it will be stuck with these features for a long time: Because the Y chromosome does not recombine (that is, it does not undergo sequence shuffling during reproduction), it is slow to evolve. On the other hand, this renders it useful in molecular anthropology, which uses DNA to deduce various relations among Homo sapiens during the past 200,000 years.

With the annotation of the human genome, a lot of progress had been made. What is the next great challenge for genetic biologists?

Unfortunately, biologists do not presently know how to combine a specific set of proteins to provide a cell with a particular function. Nature miraculously does this automatically. So the next great goal in understanding life is to figure out how proteins collectively interact to carry out cellular processes. At the genetic level, biologists must learn to deduce the biological consequences of having a whole ensemble of genes turned on.

We are already entering the age of genetic-based medicine. The new knowledge of the human nucleotide sequences will accelerate the development of therapeutic drugs that function at the molecular level. More accurate medical diagnoses will be available. Doctors will be able to address the fundamental causes of countless human disorders and will have a better change of predicting the side effects of drugs. On the horizon are cures for cancer and heart disease.

Eventually, scientists will be able to identify all of the genes contributing to a given disease. Individuals will know which sicknesses they are most at risk, giving them the possibility of making health-driven lifestyle changes or of taking preventative medical steps. Doctors will be able to tailor treatment to individuals.

The human genome sequence is a powerful tool for gaining insight into our genetic heritage and where we stand in the evolutionary scheme of things. The evolutionary tree can be determined by comparing the genomes of Earth's species. Eventually, we shall be able to take control of our own biological destiny when scientists learn to manipulate the human genome at will. No longer will we be at the mercy of the forces of natural selection. We shall be able to modify in part our vital essence. Initially, the goal will be to correct defective genes. But gradually genetic manipulation will expand to allow couples to select features of their offspring. "Pro-choice" will take on a new meaning. At some point, scientists will have almost complete mastery of the genome. Moreover, genetic manipulation will not be only confined to humans. Long before it is used on mankind, it will applied to animals and plants.

One can imagine the genetics-dominated world of the late 21st century: There will be fruits, vegetables and meats that are genetically modified for higher nutritional value. Sheep, mink, pigs, cows and other livestock will have their genes adjusted to yield higher output. Zoos will house unusual animals that differ notably from the animals from which they were derived. In place of refineries will be vast vats of swamp-like liquids containing bacteria, who, like domesticated farm animals, will produce high-tech genetically designed products that will provide a wide range of humanity's needs: food, energy, chemicals and medicines. Manipulating the genes of humans and living creatures will allow mankind to do what has been traditionally attributed to God. Indeed, President Clinton described the human genome as "the language in which God created Man." In response, Sydney Brenner of the Salk Institute for Biological Studies in San Diego said, "Perhaps now we can view the Bible as the language in which Man created God."

http://www.jupiterscientific.org/sciinfo/genome.html

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