一篇36套上的阅读

sodapengUID: 3242849

What causes a helix in nature to appear with either adextral("right-handed, "or clockwise) twist or a sinistral("left-handed," or counterclockwise) twist is one of themost intriguing puzzles in the science of form. Most spiral-shaped snail species are predominantly dextral. But at one time, handedness (twist direction of the shell) was equally distributed within some snail species that havebecome predominantly dextral or, in a few species, predominantly sinistral. What mechanisms, controlhandedness and keep left-handedness rare?

It would seem unlikely that evolution shoulddiscriminate against sinistral snails if sinistral and dextralsnails are exact mirror images, for any disadvantage that asinistral twist in itself could confer on its possessor isalmost inconceivable. But left- and right-handed snails are not actually true mirror images of one another. Their shapes are noticeably different. Sinistral rarity might, then, be a consequence of possible disadvantages conferred by these other concomitant structural features. In addition, perhaps left- and right-handed snails cannot mate with each other, having incompatible twist directions.
Presumably an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thuskeeping the rare form rare or creating geographicallyseparated right- and left-handed populations.

But this evolutionary mechanism combiningdissymmetry, anatomy, and chance does not provide an adequate explanation of why right-handedness should have become predominant. It does not explain, for example, why the infrequent unions between snails of opposing hands produce fewer offspring of the rarer tha the commoner form in species where each parent contributes equally to handedness. Nor does it explain why, in a species where one parent determines handedness,a brood is not exclusively right- or
left-handed when the offspring would have the same genetic predisposition. In the European pond snail Lymnaea peregra, a predominantly dextral species whose handedness is maternally determined, a brood might beexpected to be exclusively right- or left-handed—and this often occurs. However, some broods possess a few snails of the opposing hand, and in predominantly sinistralbroods, the incidence of dextrality is surprisingly high.

Here, the evolutionary theory must defer to a theory based on an explicit developmental mechanism that can favor either right- or left-handedness. In the case of Lymnaea peregra, studies indicate that a dextral gene is expressed during egg formation; i.e., before egg fertilization, the gene produces a protein, found in the cytoplasm of the egg, that controls the pattern of cell division and thus handedness. In experiments, an
injection of cytoplasm from dextral eggs changes the pattern of sinistral eggs, but an injection from sinistral eggs does not influence dextral eggs. One explanation for the differing effects is that all Lymnaea peregra eggs begin left-handed but most switch to being right-handed. Thus, the path to a solution to the puzzle of handedness in all snails appears to be as twisted as the helix itself.
(472 words)

先贴上原文 第29套 第二篇长阅读

sodapengUID: 3242849

主要是第二段内部的逻辑不是很懂
It would seem unlikely that evolution should discriminate against sinistral snails if sinistral and dextralsnails are exact mirror images, for any disadvantage that a sinistral twist in itself could confer on its possessor isalmost inconceivable （不知道左右手螺旋是不是完全镜面对称和sinistral 的disadvantage什么关系 ？）. But left- and right-handed snails are not actually true mirror images of one another. Their shapes are noticeably different. Sinistral rarity might, then, be a consequence of possible disadvantages conferred by these other concomitant structural features.（这里又提到了这两个其实不是标准的镜面对称，因此sinistral 其实是other concomitant structure ） In addition, perhaps left- and right-handed snails cannot mate with each other, having incompatible twist directions. Presumably an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thuskeeping the rare form rare or creating geographicallyseparated right- and left-handed populations.
完全没有理解这个提到mirror image 是什么意思。。？什么用途。。= =
求分析。。

sodapengUID: 3242849

小小ps一下。。
觉得最近做阅读很有手感。。错误率也明显下降。但是我觉得还是和36套最后几套都比较简单的缘故= =。。
不过感觉自己的做阅读的时候能够回想了，能够边看边思考。。和以前比是个进步。、
哈哈。小鼓励下自己~~
其实顶一下贴哈哈~

sodapengUID: 3242849

哎哎。。
木人理我。。= =
再发一篇。还是不太懂结构。。。

sodapengUID: 3242849

An experiment conducted aboard Space Lab in 1983 was the first attempt to grow protein crystals in the low-gravity environment of space. That experiment is still cited as evidence that growing crystals in microgravity can increase crystal size: the authors reported that they grew lysozyme protein crystals 1,000 times larger than crystals grown in the same device on Earth. Unfortunately, the authors did not point out that their crystals were no larger than the average crystal grown using other, more standard techniques in an Earth laboratory. No research has yet produced results that could justify the enormous costs of producing crystals on a large scale in space. To get an unbiased view of the usefulness of microgravity crystal growth, crystals grown in space must be compared with the best crystals that have been grown with standard techniques on Earth.
可能是我前后文的句子理解不是很到位。。
不是很清楚这里提cost是干什么？
前面说在太空合成的pr并没有比在地球用其他更标准的办法合成的pr大。然后后面就接花费问题。
然后后面的best crystal 也没有太明白哎。。为什么要拿太空上合成的晶体和地球上合成最好的晶体比较？是因为在太空合成花费多？？