In a nutrient medium that lacks histidine, a thin layer of agar containing around 10^9 Salmonella typhimurium histidine auxotrop
h produces around 13 colonies over a two day incubation period at 37 degrees centigrade. How do these colonies arise in the absence of histidine? The experiment is repeated in the presence of 0.4 micrograms of 2-aminoanthracene. The number of colonies the number of colonies produced over 2 days exceeds 10,000. What does this indicate about 2- anthracene? What can you surmise about its carcinogenicity?
Reverse mutations in the colonies enabled to recover the ability to synthesize histidine. The 2-aminoanthracene is a chemical agent that induce mutations and therefore it is potentially a carcinogen.
Explanation:
A reverse (suppressing) mutation is a type of mutation capable of restoring the activity of previously mutated genes. On the other hand, 2-aminoanthracene is an aromatic amine carcinogen capable of inducing hepatic and skin tumors. In this case, 2-aminoanthracene has been used to induce reverse mutations at <em>loci</em> responsible for the synthesis of histidine.
It is all about the tilt of the Earth’s axis. Many people believe that the temperature changes because the Earth is closer to the sun in summer and farther from the sun in winter. In fact, the Earth is farthest from the sun in July and is closest to the sun in January!
If they are only made of one element (which I'm assuming they are because the question doesn't say otherwise), then they must all be made of the same kind of atom. Only one kind of atom (in terms of protons) corresponds to one element.