In 1941, George Beadle and Edward Tatum, respectively a geneticist and a biochemist, wished to determine whether mutations can lead to nutritional requirements. For this they required an organism whose life cycle and genetics was worked out and that could be grown on a simple medium of known chemical composition so that any mutation-induced nutritional deficiency could be identified simply by supplying the fungus with a known metabolite. The organism of choice was Neurospora crassa as it requires only a simple minimal salt and sugar medium with only biotin supplement. Beadle and Tatum irradiated Neurospora conidia with x-rays to induce mutations. The irradiated conidia were used to cross a culture of the opposite mating type and the ascospores that formed were tested for mutant phenotypes (Figure 5.11). Strains were selected on the basis of
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