12.1 1. What is a model organism, and why was Neurospora a good model for studying biochemical genetics? A model organism is an organism that can be easily grown in a laboratory or easily observed in a field study which allows the phenomenon to be studied. Neurospora (bread mold) is a good model because it is haploid for most of its life and thus does not have dominant/recessive relationships. It also is easy to culture and grows well in a laboratory. 2. How were Beadle and Tatum’s experiments on Neurospora set up to determine, on the basis of phenotypes of mutant strains, the order of a biochemical pathway? After the wild type mold was treated with X-ray mutant strains were produced. These strains could not grow without excess nutrients (called auxotrophs=”increased eaters”). If an organism cannot convert one particular compound to another, it presumably lacks an enzyme required for the conversion, and the mutation is in the gene that codes the enzyme. Each gene specifies a particular enzyme.
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