Question

. 22. Researchers investigated the habitat preferences of two species of garter snakes, Thamnophis sirtalis and Thamnophis atratus. To create a choice chamber, the researchers built a meshed enclosure and positioned one end of the enclosure at the edge of a small pond. Zone I of the enclosure was located in the water, whereas zone IV of the enclosure was located 2-3 meters away from the water, as represented in the figure below. Snakes inside the enclosure were able to move freely between zones. In a series of experiments, the researchers introduced a single snake into zone IV of the enclosure at 7:00 A.M. The researchers recorded the lotation of the snake at six time points throughout the day. In a related experiment, the researchers introduced two snakes, one of each species, into the enclosure at the same time and observed the location of each of the two snakes at the same six time points as before. The researc repeated both the one-snake and two-snake experiments using different individual snakes of each species. The results are presented in the table.

Answer 1

Answer: C. The two species of snakes have different genetic mutations in the SCN4A gene.

If the resistance is found to be due to two different mutations on the same gene, two exclusive mutations not present in the other species, then it proves that the mutations arose independently in them conferring resistance.

Option A is wrong in this case as just presence of food in fossil stomach indicates that they ate the same TTX contaning food and they are resistant to it. It tells nothing about the origin of mutations.

Option B is wrong as both species could have arose from a single ancestral species containing the resistance mutation, in which case the mutation needs to have arose only once.

Option D is wrong as this merely indicates that the two species are closely related and doesn't say anything about the mutation, or the origins of mutation.