The author regards the idea that differentiation is triggered randomly when paired claws remain intact as答案解析-雷哥GRE

雷哥网GRE > 阅读&逻辑 > 1994 > 4868

1994 -4868【hard】 00:00:00 关闭计时

纠错

The two claws of the mature American lobster are decidedly different from each other. The crusher claw is short and stout; the cutter claw is long and slender. Such bilateral asymmetry, in which the right side of the body is,in all other respects, a mirror image of the left side,is not unlike handedness in humans. But where the majority of humans are right-handed, in lobsters the crusher claw appears with equal probability on either the right or left side of the body.

Bilateral asymmetry of the claws comes about gradually. In the juvenile fourth and fifth stages of development, the paired claws are symmetrical and cutter like. Asymmetry begins to appear in the juvenile sixth stage of development, and the paired claws further diverge toward well-defined cutter and crusher claws during succeeding stages. An intriguing aspect of this development was discovered by Victor Emmel. He found that if one of the paired claws is removed during the fourth or fifth stage, the intact claw invariably becomes a crusher.while the regenerated claw becomes a cutter. Removal of a claw during a liter juvenile stage or during adulthood, when asymmetry is present,does not alter the asymmetry; the intact and the regenerate claws retain their original structures.

These observations indicate that the conditions that trigger differentiation must operate in a random,manner when the paired claws are intact but in a nonrandom manner when one of the claws is lost. One possible explanation is that differential use of the claws determines their asymmetry. Perhaps the claw that is used more becomes the crusher.This would explain why, when one of the claws is missing during the fourth or fifth stage, the intact claw always becomes a crusher. With two intact claws, initial use of one claw might prompt the animal to use it more than the other throughout the juvenile fourth and fifth stages, causing it to become a crusher.

To test this hypothesis, researchers raised lobsters in the juvenile fourth and fifth stages of development in a laboratory environment in which the lobsters could manipulate oyster chips. (Not coincidentally, at this stage of development lobsters typically change from a habitat where they drift passively, to the ocean floor where they have the opportunity to be more active by burrowing in the substrate.Under these conditions, the lobsters developed asymmetric claws, half with crusher claws on the left, and half with crusher claws on the right. In contrast, when juvenile lobsters were reared in a smooth tank without the oyster chips, the majority developed two cutter claws. This unusual configuration of symmetrical cutter claws did not change when the lobsters were subsequently placed in a manipulatable environment or when they lost and regenerated one or both claws.

The author regards the idea that differentiation is triggered randomly when paired claws remain intact as

irrefutable considering the authoritative nature of Emmel’s observations likely in view of present evidence contradictory to conventional thinking on lobster-claw differentiation purely speculative because it is based on scattered research and experimentation unlikely because of apparent inconsistencies with theories on handedness in humans

正确答案： B 耗时：

该题平均耗时：4分4秒，平均正确率：36 %，难度系数：5 。该题由网友lgw19070提供。更多GRE题目请点击上传

做题笔记

网友解析

我有更好的解析

预约名师一对一题目解析课程

题目讨论 (如果对题目有任何的疑惑，欢迎在这里提出来，大家会帮你解答的哦~)

发表讨论

230419a

第一段最后一句

2楼 | 2020-11-12 16:52:06 回复

206708sqakc

These observations indicate that the conditions that trigger differentiation must operate in a random,manner when the paired claws are intact but in a nonrandom manner when one of the claws is lost. One possible explanation is that differential use of the claws determines their asymmetry. Perhaps the claw that is used more becomes the crusher.This would explain why, when one of the claws is missing during the fourth or fifth stage, the intact claw always becomes a crusher. With two intact claws, initial use of one claw might prompt the animal to use it more than the other throughout the juvenile fourth and fifth stages, causing it to become a crusher. 定位大致在这段，但是不确定用排除法好像也可以

1楼 | 2019-11-21 15:18:52 回复

做题笔记

网友解析

题目讨论 (如果对题目有任何的疑惑，欢迎在这里提出来，大家会帮你解答的哦~)

请选择错误类型：

请描述一下这个错误：

关于GRE

关于课程

联系我们