Question

Relationship between genes and enzymes was discovered by
(A)Waldeyer
(B)W. Johannsen
(C)Bridges
(D)Beadle and Tatum

Answer 1

Hint: The relationship between genes and enzymes was discovered by two scientists and these scientists also irradiated a large number of Neurospora and thereby also produced some organisms with mutant genes.

Complete answer:
 Relationship between genes and enzymes was discovered by Beadle and Tatum. The hypothesis One gene One enzyme was experimentally proved by Beadle and Tatum by using bread mould Neurospora. The one gene, one enzyme hypothesis is that the concept of each gene encodes one enzyme. Today, we all know that this concept is usually (but not exactly) correct.
The British medical doctor Sir Archibald Garrod, was the first one to suggest that genes were connected to enzymes. Beadle and Tatum then confirmed Garrod's hypothesis by using genetic and biochemical studies of the Rhizopus nigricans Neurospora.
Beadle and Tatum identified Rhizopus nigricans mutants that were unable to form specific amino acids. In all, a mutation had "broken" an enzyme needed to create a particular amino alkanoic acid.

Additional Information: Some genes don't encode polypeptides. Some genes actually encode functional RNA molecules instead of polypeptides.
Although the "one gene-one enzyme" concept isn't perfectly accurate, its core idea – that a gene typically specifies a protein during a one-to-one relationship – remains helpful to geneticists today.
So, the correct answer is ‘Beadle and Tatum’.

Note: There was a reason why Beadle and Tautam used bread molds. The Neurospora cells can be easily grown in the laboratories on simple mediums like nutrient broth or gel whose chemical composition was completely known and controlled during the experiment. Even the cells require the minimal medium to grow on, a nutrient source with just sugar, salts, and one vitamin (biotin).