Question

One gene - one enzyme relationship was established for the first time in
A. Neurospora crassa
B. Salmonella typhimurium
C. Escherichia coli
D. Diplococcus pneumoniae

Answer 1

One gene one enzyme, is an idea where the genes act through the production of enzymes, with each gene responsible for producing single enzyme, that in turn affects a single step in metabolic pathway, and this concept of one gene and one enzyme was proposed by Hedge beader and Edward Tatum.

Complete step by step answer: Firstly one gene and one enzyme was identified in Neurospora Crassa.
The experiment that is done on this is called biochemical genetics, the development of one gene one enzyme is often considered as the 1st significance result called molecular biology.
While doing the experiment on the Neurospora they noted that there is a system that controls or regulates the specific reaction in the system either by acting directly as enzyme or by determining the specialties of the enzyme.
So that the experiments on the Neurospora and as well as on the other organisms such as E Coli, produce evidence that each step in the metabolic pathway is usually controlled by a single gene.
Where the gene is visualized directly and the final configuration of the protein molecule determines its specificity.
Whereas in the year 1950, advances in biochemical genetics made this concept of one gene one enzyme very unlikely.
So the correct answer is Neurospora Crassa and the correct option is A.

Note: In 1957, some scientists showed through electrophoresis that genetic variation in protein could be limited to difference in just a single polypeptide chain and in a multimeric protein, which leads to one gene one polypeptide hypothesis.