Two kinds of geneticist

The two kinds of inheritance produced two kinds of geneticist, the single-gene Mendelians, and the many-gene biometricians. During the early 1900s, a bitter scientific dispute arose in which it was assumed that, if one side was right, the other must be wrong. The Mendelians had science on their side, with Mendel's laws, strongly supported by the discovery of chromosomes, and the elucidation of their role in sexual recombination and inheritance. The biometricians had practical experience on their side, because every known character of any economic importance in domesticated plants and animals was inherited quantitatively.

The dispute continued until the discovery of polygenic inheritance a couple of decades later. In the meanwhile, Biffin (1905) had published a seminal paper entitled Mendel's Laws of Inheritance and Wheat Breeding, showing that resistance to stripe rust (Puccinia striiformis) of wheat was controlled by single genes. Suddenly, the Mendelians had single-gene characters of economic importance, and they pursued this advantage with great vigour. Indeed, they pursued it with such vigour that they soon dominated plant breeding. (Interestingly, there were no single-gene characters of any economic importance in farm animals, and the biometricians maintained control of all animal breeding during the twentieth century. Furthermore, farmers rather than geneticists have made many of the recent improvements in animal breeds, and all of these improvements are quantitative.)

The two kinds of genetics quickly led to two different kinds of plant breeding. The Mendelians devised a method of transferring a single resistance gene from a wild plant into a cultivar by back-crossing. This technique was known as pedigree breeding, and it soon dominated the whole of plant breeding. The biometricians used recurrent mass selection, which had been used by farmers since the dawn of agriculture. It is also the most common form of genetic control in wild ecosystems and wild pathosystems. This breeding method emphasises the many-gene, quantitatively inherited characters.

0 0

Post a comment