THE SECRET OF LIFE

What made us human? Our genome provides answers. The human genome was completely sequenced by scientists in 2000, revolutionizing anthropology, psychology, medicine, palaeontology, and every other science. Popular science writer Matt Ridley explains everything about the genome lucidly in his book ‘Genome: An Autobiography of a Species in 23 Chapters’.

Our body has approximately 100 trillion cells, and each cell has a nucleus, inside which is located a complete set of the genome. One set of the genome comes from the father, and the other from the mother; each set contains approximately 60,000 to 80,000 genes on the chromosomes. The human genome comprises twenty-three pairs of chromosomes. Ridley gives a beautiful analogy by asking us to imagine that the genome is a book with twenty-three chapters called chromosomes; each chapter has several thousand stories called genes; each story contains paragraphs called exons, which are interrupted by advertisements called introns; each paragraph is made up of words called codons, and each word is written in letters called bases. The genome is written entirely in three-letter words, using only four letters called A (Adenine), C (Cytosine), G (Guanine), and T (Thymine). The book contains one billion words as long as 800 Bibles. If you read the genome at the rate of one word per second for eight hours a day, it would take you one century to complete it. He states that the genes are recipes for both anatomy and behaviour.

The key to life is information, which is passed on from one generation to another through genes. A record of our past is etched into our genes. Heredity is a modifiable stored programme. The three-letter words of the genetic code are the same in every creature, and the unity of life is an empirical fact. A human cell consists of 23 pairs of chromosomes. Chimpanzees, gorillas, and orangutans have twenty-four pairs of chromosomes. He asserts that the human species is by no means the pinnacle of evolution. There is no such thing as evolutionary progress; every species on the planet is unique in its own way. We are approximately ninety-eight per cent chimpanzees, and the three per cent difference makes us human.

Hermann Joseph Muller won the Nobel Prize for his great discovery that genes are artificially mutable. Artificial mutation kick-started modern genetics, as genes were recipes for proteins; mutations were altered proteins made by altered genes. James Watson and Francis Crick discovered that genes are composed of DNA (deoxyribonucleic acid), which contains a four-letter code (A, C, G, and T) written on its double-helix structure.

By mapping the genes, scientists can know about the genetic basis for certain diseases, such as a gene on chromosome 3 that, when broken, causes alkaptonuria (black urine disease in premature arthritis); another gene on chromosome 4 is the cause, when elongated, of Huntington’s chorea (neurodegenerative disorder), and chromosome 5 is the leading cause of asthma. It is found that you either have mutations, in which case you get these diseases, or you don’t. Sometimes, multiple genes affect in multiple ways, which is called pleiotropy.

Ridley cites a case study of twin sisters separated after birth and shows that the power of instinct is more powerful than upbringing. One selects the environment that suits one’s innate tendencies, rather than adjusting one’s innate tendencies to the environments one finds oneself in, proving that the genetic influences are not frozen at conception and that environmental influences are not inexorably cumulative. The X and Y chromosomes are called sex chromosomes. X chromosomes are found in women and Y chromosomes in men. If Y chromosomes are inherited from your father, you will be a man; if X chromosomes are inherited from your father, you will be a woman. In our country, society wrongly blames women for giving birth to a girl child, while it is the male chromosome that determines the sex of a child.

The mind drives the body, which drives the genome. Ridley discloses that some of the personality traits of human beings come from chromosome 11, on which lies the D4DR gene. Geneticists found that the longer the D4DR gene, the lower the responsiveness to dopamine, which results in a lack of initiative and motivation, whereas a short D4DR gene implies a high responsiveness to dopamine, which may lead to adventurism to seek more pleasure. Some geneticists estimated that novelty seeking is about forty per cent heritable. Ridley states that upbringing mattered a good deal. But intrinsic personality plays just as big a role. He also tells about a gene called the serotonin-transporter gene on chromosome 17, which is a chemical manifestation of personality. If you have a high level of serotonin in your brain, you will probably be a compulsive person. He clarifies that our genes are programmed not only to produce a social behaviour, but to respond to it as well, and social influences upon behaviour work through the switching on and off of genes.

Ridley pointed out that male behaviour is systematically different from female behaviour in most species, and the difference has an innate component. He says instinct is genetically determined behaviour; learning is behaviour modified byexperience.

Genome sequencing not only enriched our knowledge about what characteristics are inherited by us, but also developed technology to manipulate the genetic structure by editing genes to eliminate harmful ones that cause genetic diseases or to produce more efficient and beneficial species. Genetically engineered food plants are a new fad now. People suffering from Severe Combined Immunodeficiency syndrome are now being treated with genetic engineering. Ridley states that heart disease is a preventable and treatable condition, and it can be easily treated if a person has the E2 gene, which is sensitive to fatty and cholesterol-rich diets by warning aboutthem.