Question

A mutant organism that will not grow on a minimal medium but does so on addition of some growth factors is known as

• A. Axoneme
• B. Autotroph
• C. Auxotroph
• D. Heterotroph

Answer 1

The correct option is C Auxotroph

Auxotroph is an organism, such as a strain of bacteria, that has lost the ability to synthesize certain substances required for its growth and metabolism as the result of mutational changes. The method of replica plating implemented by Esther Lederberg included auxotrophs that were temperature-sensitive; that is, their ability to synthesize was temperature-dependent. (Auxotrophs are usually not temperature-dependent. They can also depend on other factors). Multiple auxotrophs can also coexist at the same time, within the same organism.
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 in 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.