rationalskepticism.org

kyrani99 wrote:

Rumraket wrote:

kyrani99 wrote::lol: Speaking of untruths, I have taken a closer look at the Ames test. It is groundless. All the chemicals that they are naming mutagens do no cause mutations that lead to a beneficial change in the bacteria.

[Citation Needed]

The Ames test http://www.biology-pages.info/A/AmesTest.html
The article says:
"The bacterium used in the test is a strain of Salmonella typhimurium have been altered so that they carry a defective (mutant) gene making it unable to synthesize the amino acid histidine (His) from the ingredients in its culture medium. However, some types of mutations (including this one) can be reversed, a back mutation, with the gene regaining its function. These revertants are able to grow on a medium lacking histidine."

This citation fails to prove evidence of the claim that none of the changes are beneficial.

kyrani99 wrote:That is at the end of a positive test the bacteria no longer need histidine to grow because they can make their own. So they have undergone a back mutation, which makes the gene functional again. A "gain of function" is a beneficial change in the bacteria.

A beneficial change is one that results in increased reproductive success, whether it is "gain of function" or not. Regardless, this one IS a gain of function. The function gained is histidine biosynthesis. The bacterium was deliberately engineered not to be able to do it, and has subsequently mutated so it can. So the function Histidine Biosynthesis was gained. No amount of desperate ad-hoc reasoning will get around this.

kyrani99 wrote:However the bacteria can make the change spontaneously.

No, bacteria can't "make" the change spontaneously through their own volition or whatever silly stuff it is you imagine.

All mutations can happen spontaneously during replications of the bacterial chromosome, but that is irrelevant. The question is if a compound is mutagenic, as in: it causes an increase in the rate of spontaneous mutations, beyond the background rate(the normal rate of mutations). The more mutagenic it is, the more it will increase the rate of spontaneous mutations above the normal background rate.

But even without mutagens, mutations will still occasionally creep in. In these bacteria, excision repair has been forced off, which increases their sensitivity to mutagens while also increasing the background level of mutations. That's why even the negative controls will invariably produce lots of mutants.

kyrani99 wrote:In this case it is called a false positive.

There is no "false positive" involved here.

In the Ames test you make several plates, some for negative control(no suspected mutagen added) and some for testing the mutagen(suspected mutagen is added). If the number of colonies on the control plates are lower than on the plates with the suspected mutagen, then the mutagen is in fact a mutagen since it caused a higher than average(more colonies on the plates with the mutagens than on the negative control plates) number of mutants.