2003-1-44

44-47 biology
I’ve mentioned how DNA have solved many mysteries in biology. And today I want to talk about how it might relate to hypothesis about the travels of the green turtle. Every winter some green turtles make a 2000 km journey from Brazil to Ascension Island in the middle of Atlantic, where they mate and lay eggs. But the question is why do they travel so far to lay their eggs? One researcher hypothesized that there are two parts to the explanation. One is natal homing, the instinct that drives green turtles to always return to the beach where they were hatched. The second part has to do with continental drift, the theory that the positions of earth continents have changed considerably overtime. Brazil and Ascension Island were once much closer together, and continental drift drove them apart. But the turtles kept on going back to the island where they hatched. However another scientist question this explanation on the ground that it would be very unlikely that conditions would allowe generations of turtles over hundreds of millions of years to keep going back to the same nesting ground every single year. So, what is the connection to DNA? Well, there are groups of green turtles that nest in locations other than the Ascension Island. If green turtles always return to the place where they were hatched, then the turtles that have been going to the Ascension Island to nest would’ve been genetically isolated long enough to have DNA that was very different from the green turtles that nest else where. But when scientists examine DNA from these turtles, their DNA wasn’t that different from the DNA of the turtles that go to Ascension Island. Do you have a shock? Well, we still don’t know the answer to the question about why a certain group of turtles go to Ascension Island, but this study was a nice example of the usefulness of DNA analysis to biology.
44. (A) A possible explanation for why green turtles nest in certain locations.

(B) Physical differences among various groups of green turtles.

(C) Several examples of mating behavior in green turtles.

(D) The impact of continental drift on the diet of green turtles.

答案為a,可是文中並沒有提到 ‘nest”吧…..我選C

个人还是比较倾向于a，因为主题题型的答案，不会是c，而且从开头和结尾，能够看出，是关于certain location的问题，尽管没有提到nest，但还是可以理解的。重要的还是开头和结尾的两三句话。

感謝感謝^^