in genetics, a strain is said to be auxotrophic if it carries a mutation that renders it unable to synthesize an essential compound. for example, a yeast mutant with an inactivated uracil synthesis pathway gene is a uracil auxotroph (e.g., if the yeast orotidine 5'-phosphate decarboxylase gene is inactivated, the resultant strain is a uracil auxotroph). such a strain is unable to synthesize uracil and will only be able to grow if uracil can be taken up from the environment. this is the opposite of a uracil prototroph, or in this case a wild-type strain, which can still grow in the absence of uracil. auxotrophic genetic markers are often used in molecular genetics; they were famously used in beadle and tatum's nobel prize-winning work on the one gene-one enzyme hypothesis, connecting mutations of genes to protein mutations. this then allows for biosynthetic or biochemical pathway mapping that can help determine which enzyme or enzymes are mutated and dysfunctional in the auxotrophic strains of bacteria being studied.