The ames test is used to identify potential carcinogens. a compound tested resulted in a few scattered colonies growing on the media, similar to the control plate with no disk. what does this result imply? a. the compound in the disk is so toxic that it inhibits almost all growth on the plate. b. the few colonies that grew are resistant to the compound. c. the few colonies that grew contain reversion mutations that allow them to grow on media without histidine. d. the compound in the disk is not mutagenic so there was no increase in the reversion rate.

The correct answer is option D.

Explanation:

In the given case, a similar amount of colonies is witnessed in both control as well as the test plate. This concludes that it does not influence the organism, thus, there was no enhancement in the rate of reversion, that is, the number of colonies in the test plate does not get decrease. Thus, the compound in the disc is not mutagenic as there was no increase in the reversion rate.

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?