SCIENCE Tailoring genes

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GENETIC engineering is the latest development in a long line of human genetic manipulation aimed at altering the genetic complement of commercially viable or useful organisms.

When man settled to an agrarian economy this process started • with the 'selection' of the most suitable strains of animals and crops for interbreeding and cultivation. Wheat is the result of one such process, having six times the gross genetic complement of its ancestor Triticum monococcus, 8000 years ago.

Modern genetic engineering covers two general techniques, cloning and DNA technology. Cloning involves the removal of the whole DNA complement from the nucleus of a cell of the desired replicant (a replicant is the individual to be cloned and its offspring). This DNA is then placed by microsurgical techniques into the empty nucleus of a recipiant fertilised sex cell of another organism of the same species, and the cell is then allowed to divide by binary fission to give eight daughter cells.

Cells Each of these celis may be used to repeat the process until the desired number of replicant sex cells are implanted. Once this is done, the sex cells are allowed to undergo replication and normal pregnancy in a recipient organism of the same species.

This process results in one or more females producIng up to several dozen genetically identical offspring. It was originally perfected in the African Claw Toad (Zenopus laevis) as its fertilisation and incubation are external to the body, but recently it has been successfully undertaken in laboratory mice, which are mammals, as are humans.

This process has the advantage that genetically identical organisms are of great use in the laboratory for drug testing and other related work, where identical organisms give more accurate results. Otherwise, commercially, genetically identical higher organisms are of little. interest except in pure research.

On the other hand, DNA technology holds much commercial promise. This involves the cloning of a simple gene and not the whole genetic complement.

The whole basis of DNA technology is that genes are composed of DNA, which holds in its structure the ability to "code' for the manufacture of proteins in cells. This is the "central dogma' of molecular genetics.

The central dogma relates to the principle by which the 'code' held on the DNA is copied into a mirror code. held on mRNA. The mRNA code is then translated at sites known as ribosomes, by the 'anticodons' of tRNA. The IRNA molecules carry single amino-acids (the building blocks of proteins) which are coupled • together into long chains of polypeptides to give the required protein.

The aim of DNA recombinance technology is to )VI he :01 place a viable gene into the genetic complement of a rapidly reproducing microorganism, usually bacterium; in order for that gene to be expressed as protein.

The advantages of this are that bacteria are cheaper and easier to grow than many advanced animal and plant cells and that they have a higher rate of metabolism and reproduction, hence producing more protein on less substrates in a shorter time.

For instance, somatostatin is a pituitary growth hormone used in treatment of irregular human growth patterns. It was originally isolated from sheep brains at the rate of 5mg (5/1000ths of a gram) per 500,000 brains. Gene 91 from human sources produces a more effective version of the same hormone, when implanted in the bacteria Escherichia coli. This involved quantities of less than five litres of culture of E. coli to produce similar concentrations of somatostaDNA technology itself is an extension of a naturally occuring phenomenon in which parts of the DNA complement of one bacteria, the 'donor? , are transferred to the genetic complement of another, the 'recipient' by the action of a prophage or temperate bacterial virus.

Genes The gene or genes carried I by this process cause excision and loss of the aplementary genes on the recipient chromosome. So that when protein production occurs the protein produced is that of the donor not the recipient original complement.

GLOSSARY DNA- deoxyribosenucleic acid. mRNA - messenger ribosenucleic acid. tRNA - transfer ribosenucleic acid.

Polypeptide - short chain protein.

Amino acids - basic BE protein structure.

Binary fission - a simple process of cell division. SOURCES New Scientist, 26 August 1982.

Biologist, September 19, 1982.

Report of the Working Party on the Experimental Manipulation of the Genetic Composition of Micro-organisms, January 1975, Cmnd 5880.

Microbial and Molecular Genetics, Fincham. THE West German constitution is studded with references to individual rights. The experience of Nazism led its authors to confirm - in writing at least - the 'dignity of man' When Hasan Aksoy fled from Turkey to Germany, hoping to be granted political asylum there, he probably had little faith in bourgeois constitutions, but he had little choice.

AKSOV left-wing arrested in Antep in southeastern Turkey by military police. He was arrested for selling the revolutionary paper 'Kawa' ', but managed to escape to Germany.

Last year he applied for political asylum. The basic case was clear: if he returned to Turkey he would be killed - probably after being tortured. Back came abuse happen all the time in Turkey, and politically active Kurds are not the only victims...

"Thus any tortures the appellant might have to endure in the event of his being involved in a judicial process cannot be defined as political persecution...' • So far so bad! But then the explanation went on to concede that there might be a case for political asylum if the state in whose name officials carry out torture instigate and approve it or accept it happens but do nothing.

In other words they completely accept Turkish dictator Evren's word that torturers will be punished. Obviously the judges do not see the slightest hint of cynicism behind Evren's confession last year to an interviewer from the West German magazine, 'Spiegel': "There's always been