Notes on one gene one enzyme hypothesis of botany for bsc first year
Answers
a) Beadle and coworkers found that the red eye colour of Drosophila melanogaster is controlled by two genes and is caused by the blending of brown and vermillion pigments. A piece of larva destined to form vermillion eye can be made to produce red eye colour if it is placed in the body cavity of larva having red eye because the latter provides its enzyme for brown colour which the transplant lacks.
(b) In 1944, Beadle and Tatum irradiated Neurospora crossa with X-rays and obtained a number of nutritional mutants called auxotroph’s. An auxotroph or nutritional mutant is that mutant which is not able to prepare its own metabolites from the raw materials obtained from outside. Therefore, it cannot live in natural environment but can be maintained in culture by providing the required metabolites. The wild type is called prototroph.
A prototroph or wild type is the normal individual which can synthesize all the complex metabolites required for its growth from raw materials obtained from outside. It can grow in the laboratory on minimal medium consisting of ammonia, sugar, salts and biotin.
Beadle and latum (Fig. 8.2) found three types of auxotroph’s requiring amino acids ornithine, citrulline and arginine. The prototrophs were found to have amino acid arginine in their body. Obviously it has been synthesized from ammonia and sugar of the minimal medium. Auxotroph requiring ornithine for its growth does not contain arginine and dies due to protein deficiency. When supplied with ornithine, it is found to possess arginine.