basic knowledge

KNOWLEDGE OF GENES

The twin seeds of genetic engineering were sown within a decade of each other in the id 19th century. First, in the 1860s, Gregor Mendel ( click to view a graphical illustration of his famous experiment) working in what is now the Czech Republic show that the individual features of plants were determined by discrete factors which later, in the 20th century, were given the name of 'genes'. Most of them are polygenic, which means they are brought about by combinations of different genes; and most genes are pleiotropic, which means that they affect more than one characters, often characters that seem quite unrelated to each other. The fact that most characters are polygenic and most genes are pleiotropic severely limits the scope and power of genetic engineering, at least in the present state of knowledge. "Genetic engineers' can transfer only one gene at a time and want its effects to be entirely predictable - which means that in general they must focus opon the minority of characters that have a simple genetic basis, and are determined by genes that are not highly pleiotropic.

A few years after Mendel, in 1869, and quite separately, a Swiss biochemist called Johann Friedrich Miescher working at Tubingen in Germany discovered DNA in pus cells. He called it 'nuclein' and in the 1879w he studied nuclein in the sperm of Rhine salmon and conclude that it might be 'the specific cause of fertilization'. But he died in 1095, aged just 51, and never really followed up what in truth was a fine insight.

So Mendel showed the underlying mechanism of heredity and gave rise to the science of 'classical genetics'; and Miescher discovered the material of which genes re made; and so classical genetics, which treats genes as abstractions, was able to become 'molecular genetics'.

Even before genes were known to be made of DNA - in fact from the beginning of the 20th century - it was clear that the principal task of genes is to make proteins. In particular, many proteins functions as enzymes, and the task of the enzymes is to act as catalysts and so to control the cell's metabolism, and to help to synthesize all the many other molecules of which cells are compose. Hence the genes, operating via proteins, control both the structure and the function of the cells.