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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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Dear Sir,

unfortunately, the answer is NO.

Who says that there are shortcuts, strategy to solve it in a snap.......sorry but they are misleading

The best strategy is to improve your standard English as a whole and read the entire passage, even though you do not have to focus to every detail but grasp the whole picture.

then answer the question, as it turns out they will reveal to you much more clearly.

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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
The passage says that if the two parents are sinistral, they could have predominantly dextral offspring.
So, why in q 4 A is not the answer ? A) a developmental mechanism that affects the cell-division pattern of snails

For B, we have that having a lot dextral and sinister struggle to have mate, it will lead to geographic separation. Consequently, sinister will be dominant in specific geographic location.
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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1.Which of the following would serve as an example of “concomitant structural features” (line 13) that might disadvantage a snail of the rarer form?
According to passage question:
Their shapes are noticeably different. Sinistral rarity might, then, be a consequence of possible disadvantages conferred by these other concomitant structural features.
The answer focuses on shape:
ANS: D states something about shape

2.The second paragraph of the passage is primarily concerned with offering possible reasons why
Function question:
Explain why the rarity
ANS: B

3. Which of the following accurately describes the relationship between the evolutionary and developmental theories discussed in the passage?
According to passage
But this evolutionary mechanism combining dissymmetry, anatomy, and chance does not provide an adequate explanation of why right-handedness should have become predominant.
Here, the evolutionary theory must defer to a theory based on an explicit developmental mechanism that can favor either right- or left-handedness
ANS: C

4.It can be inferred from the passage that a predominantly sinistral snail species might stay predominantly sinistral for each of the following reasons EXCEPT for
A. P4: Here, the evolutionary theory must defer to a theory based on an explicit developmental mechanism that can favor either right- or left-handedness.
B. NOT STATED
C. P2: Presumably an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thus keeping the rare form rare or creating geographically separated right- and left-handed populations.
P3: It does not explain, for example, why the infrequent unions between snails of opposing hands produce fewer offspring of the rarer than the commoner form in species where each parent contributes equally to handedness.
It states that union between opposing shapes is possible.

D. P2: In addition, perhaps left- and right-handed snails cannot mate with each other, having incompatible twist directions.
E. P2: Presumably an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thus keeping the rare form rare or creating geographically separated right- and left-handed populations.
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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Ask for more explanations in case you need

regards
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
In the European pond snail Lymnaea peregra, a predominantly dextral species whose handedness is maternally determined, a brood might be expected to be exclusively right- or left-handed—and this often occurs.

Can infer from this that dextral can be a reason for predominant sinister ?
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QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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What causes a helix in nature to appear with either a dextral (right-handed, or clockwise) twist or a sinistral (left-handed, or counterclockwise) twist is one of the most intriguing puzzles in the science of form.

The phenomenon above is quite puzzling

Most spiral-shaped snail species are predominantly dextral.

The snali usually a dexstous

But at one time, handedness (twist direction of the shell) was equally distributed within some snail species that have become predominantly dextral or, in a few species, predominantly sinistral.

Not a so clear sentence to understand. At the same time, the shape of the shell in the snail is usually of the right but in some of sub-species are towards the left

What mechanisms control handedness and keep left-handedness rare?


Why is so on the left and why it is a minority phenomenon


It would seem unlikely that evolution should discriminate against sinistral snails if sinistral and dextral snails are exact mirror images, for any disadvantage that a sinistral twist in itself could confer on its possessor is almost inconceivable.

Basically the sentence above tells us that the evolution process is even because right and left are mirror of one another


But left- and right-handed snails are not actually true mirror images of one another.

Actually left and right are NOT mirror

Their shapes are noticeably different.

They are different in shape


Sinistral rarity might, then, be a consequence of possible disadvantages conferred by these other concomitant structural features.

The left direction could be the result of certain disadvantages that as it turns out is the result of certain fatures

In addition, perhaps left- and right-handed snails cannot mate with each other, having incompatible twist directions.

The cannot match each other

Presumably, an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thus keeping the rare form rare or creating geographically separated right- and left-handed populations.


Maybe, mating two individuals of the same side is difficult and the result is that the left side is keeping a rare feature and the right and left snails are separated.


But this evolutionary mechanism combining dissymmetry, anatomy, and chance does not provide an adequate explanation of why right-handedness should have become predominant.


All the above, however, does not explain why the right side feature is predominant respect the left one

It does not explain, for example, why the infrequent unions between snails of opposing hands produce fewer offspring of the rarer than the commoner form in species where each parent contributes equally to handedness.

rarely the left and right shell feature mate. And why does this union produces more right side shells than left side.


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.

Why in those couples where the shell on one parent is the relevant, the result is left direction or right without where it (the brood) should be mainly right.

In the European pond snail Lymnaea peregra, a predominantly dextral species whose handedness is maternally determined, a brood might be expected 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 sinistral broods, the incidence of dextrality is surprisingly high.


This particular species in Europe where the individuals are usually right; the brood is not a mix. Or they are right or left where the mother is right and the offspring should be right. However, the sinistral feature is the most relevant

Here, the evolutionary theory must defer to a theory based on an explicit developmental mechanism that can favor either right- or left-handedness.

Some sort of mechanism that favorites the right side or left side should be implied

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.


For example, in the above case, a protein is the culprit of the right direction of the shell.

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.


An experiment was performed to confirm thew hypothesis above


One explanation for the differing effects is that all Lymnaea peregra eggs begin left-handed but most switch to being right-handed.

An explanation could be that the direction began left and than shift to the right


Thus the path to a solution to the puzzle of handedness in all snails appears to be as twisted as the helix itself.

We do not know yet for sure. It is a conundrum
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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Asmakan wrote:
In the European pond snail Lymnaea peregra, a predominantly dextral species whose handedness is maternally determined, a brood might be expected to be exclusively right- or left-handed—and this often occurs.

Can infer from this that dextral can be a reason for predominant sinister ?



No. See my explanation of the entire passage sentence by sentence above.
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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Question 1

Which of the following would serve as an example of “concomitant structural features” that might disadvantage a snail of the rarer form?

A) shell and body that are an exact mirror image of a snail of the commoner form
B) A smaller population of the snails of the rarer form
C) A chip or fracture in the shell caused by an object falling on it
D) A pattern on the shell that better camouflages it
E) A smaller shell opening that restricts mobility and ingestion relative to that of a snail of the commoner form


Difficult to interpret this question correctly. The wording is quite convoluted. When in these situations you have to find some other way or trick in the wording itself.

The question asks us the following : concomitant structural features”

Concomitant means AT THE SAME TIME. Two features or situations that works TOGETHER

Only E we do have TWO things that happen at the same time.
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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Questions 2



The second paragraph of the passage is primarily concerned with offering possible reasons why

A) it is unlikely that evolutionary mechanisms could discriminate against sinistral snails
B) sinistrality is relatively uncommon among snail species
C) dextral and sinistral populations of a snail species tend to intermingle
D) a theory based on a developmental mechanism inadequately accounts for the predominance of dextrality across snail species
E) dextral snails breed more readily than sinistral snails, even within predominantly sinistral populations


Presumably, an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thus keeping the rare form rare or creating geographically separated right- and left-handed populations.


Clearly, B is the right choice. The second paragraph actually tells us that the left direction are not so uncommon overall
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Question 3


Which of the following accurately describes the relationship between the evolutionary and developmental theories discussed in the passage?

A) Although the two theories reach the same conclusion, each is based on different assumptions.
B) They present contradictory explanations of the same phenomenon.
C) The second theory accounts for certain phenomena that the first cannot explain.
D) The second theory demonstrates why the first is valid only for very unusual, special cases.
E) They are identical and interchangeable in that the second theeory merely restates the first in less technical terms.


Here, the evolutionary theory must defer to a theory based on an explicit developmental mechanism that can favor either right- or left-handedness

C) The second theory accounts for certain phenomena that the first cannot explain.

Basically C is the paraphrasing of the above sentence

C is the correct answer
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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Question 4


It can be inferred from the passage that a predominantly sinistral snail species might stay predominantly sinistral for each of the following reasons EXCEPT for

A) a developmental mechanism that affects the cell-division pattern of snails

mentioned

B) structural features that advantage dextral snails of the species

N. We do not know the features why the snail goes right or left in the end. The passage is all about to find these reasons

C) a relatively small number of snails of the same hand for dextral snails of the species to mate with

mentioned

D) anatomical incompatibility that prevents mating between snails of opposing hands within the species

Mentioned

E) geographic separation of sinistral and dextral populations

mentioned
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Re: QOTD # 6-7-8-9 What causes a helix in nature to appear with [#permalink]
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