The more that is discovered about the intricate organization of the ne

Question

The more that is discovered about the intricate organization of the nervous system, the more it seems remarkable that genes can successfully specify the development of that system. Human genes contain too little information even to specify which hemisphere of the brain each of a human's 1011 neurons should occupy, let alone the hundreds of connections that each neuron makes. For such reasons, we can assume that there must be an important random factor in neural development, and in particular, that errors must and do occur in the development of all normal brains.

The most vivid expression of such errors occurs in genetically identical (isogenic) organisms. Even when reared under the same conditions, isogenic organisms are rarely exact copies of one another, and their differences have revealed much about the random variations that result from an organism's limited supply of genetic information. In isogenic Daphniae, for example, even though the position, size, and branching pattern of each optic neuron are remarkably constant, there is some variability in connectivity, and the number of synapses varies greatly. This variability is probably the result of random scatter beyond the resolution of genetic control and is best termed "imprecision," since its converse, the degree of clustering about a mean, is conventionally called "precision."

Imprecision should be distinguished from developmental mistakes: wrongly migrated neurons, incorrect connections, and the like. To use a computer analogy, minor rounding-off errors occur universally and are analogous to imprecision, but occasionally a binary digit is incorrectly transmitted, perhaps ruining a calculation, and this incorrect transmission is analogous to a developmental mistake. Thus, imprecision is a form of inaccuracy inherent within the limits of design, but mistakes are forms of gross fallibility. Both imprecision- and gross fallibility can plausibly be blamed on the insufficiency of genetic information since either could be reduced by adding more information. It is universally accepted among information theorists that codes and languages can be made mistake-resistant by incorporating redundancy. However, since the amount of space available in any information system is limited, increased redundancy results in decreased precision. For example,  \pi  when written incorrectly in English, "three point oen four two," can be understood correctly even though a typographical error has occurred. More precision could be gained, however; if those 24 spaces were filled with Arabic numerals; then 1t could be expressed to 23 significant digits, although any error would significantly change the meaning. There exists a trade-off; the more precisely a system is specified, using a given limited amount of information, the greater the danger of gross mistakes. The overall scheme by which genetic information is rationed out in organisms, therefore, must involve a compromise between two conflicting priorities: precision and the avoidance of gross mistakes.   1 
 B 
 1. Which of the following best expresses the main idea of the passage?

(A) Although studies of isogenic organisms have shown that all organisms are subject to developmental variations, there is still scientific debate over the exact causes of these variations. 
(B) Because of limitations on the amount of information contained in the genes of organisms, developing nervous systems are subject to two basic kinds of error, the likelihood of one of which is reduced only when the likelihood of the other is increased. 
(C) The complexity of an organism's genetic information means that much of the unusual variation that occurs among organisms can best be explained as the result of developmental mistakes. 
(D) New findings about the nature of the genetic control of neural development support the work of; some scientists who argue that the computer is an extremely useful model for understanding the nervous system. 
(E) The major discovery made by scientists studying the genetic control of neural development is that both imprecision and gross developmental error can be traced to specific types of mutations in specific genes.

2 
 C 
 2. According to the passage, one of the reasons it has been assumed that there is an important random element in human neural development is that

(A) genes cannot specify certain types of developmental processes as well as they can others 
(B) the intricacy of the nervous system allows small developmental errors to occur without harmful effects 
(C). the amount of information contained in the genes is less than the amount necessary to specify the location of the neurons 
(D) the number of neurons in the human brain varies greatly from individual to individual 
(E) it is theoretically impossible for an organism to protect itself completely from gross developmental mistakes

3 
 B 
 3. The author suggests which of the following about the findings of information theorists?

(A) Their findings provocatively challenge the standard explanation of redundancy·in genes. 
(B) Their findings provide useful insights into understanding the rationing of genetic information. 
(C) Their findings help to explain why imprecision can occur in neural development but not why gross mistakes can occur. 
(D) Their findings suggest that genes may be able to specify neural development more accurately than had previously been thought. 
(E) Their findings support the work of those who use computer operations as models for understanding genetic control.

4 
 E 
 4. According to the passage, of the following aspects of the optic neurons of isogenic Oaphniae, which varies the most?

(A) Size 
(B) Connectivity 
(C) Position 
(D) Branching pattern 
(E) Number of synapses

5 
 D 
 5. Which of the following best describes the organization of the first paragraph?

(A) A specific case is presented, its details are analyzed, and a conclusion is drawn from it. 
(B) A discovery is announced, its most significant application is discussed, and possibilities for the future are suggested. 
(C) A generalization is made, specific situations in which it is applicable are noted, and problems with it are suggested. 
(D) An observation is made, specifics are provided to support it, and a generalization is derived. 
(E) A hypothesis is presented, its implications are clarified, and applications of it are discussed.

6 
 A 
 6. The author uses all of the following to clarify the distinction between imprecision and gross mistake in neural development EXCEPT

(A) classification of borderline phenomena 
(B) a description of the relationship between the phenomena denoted by each term 
(C) specific examples of the phenomena denoted by each term 
(D) an explanation of at least one of the key terms involved 
(E) analogies to other types of phenomena

7 
 A 
 7. Which of the following can be inferred from the passage about the genetic information of Daphniae?

I. There is probably some degree of redundancy in the information controlling neural development. 
II. Most of the information for neural development stored in the genes is used to specify the positions of the optic neurons. 
III. There is sufficient information to preclude the occurrence of gross mistakes during neural development.

(A) I only 
(B) II only 
(C) III only 
(D) I and II only 
(E) II and III only

VRG1998 · Answer

can anyone explain Q 3 and Q7?

carcass · Answer

Q1

This is a great passage because shows how the main idea is at the very end of the passage. The assumption that it is always in the firsts paragraph is not true.

B is the answer

Q2

Which of the following can be inferred from the passage about the genetic information of Daphniae?

I. There is probably some degree of redundancy in the information controlling neural development.

Correct

II. Most of the information for neural development stored in the genes is used to specify the positions of the optic neurons.

wrong no precision is mentioned or inferred

III. There is  sufficient information  to preclude the occurrence of gross mistakes during neural development.

Wrong

All the information is in the passage. Just read carefully is the key to win the game

Regards

richirish · Answer

Took me 10 mins, 6/7 correct, last 2 questions are a bit tricky ,rest are relatively easier.

amritaarhea · Answer

Need some explanation for Question 3 and 7.
In 7, I was able to choose 1 by eliminating 2 and 3. But I was not able to find 1 from the passage directly.

Sajjad1994 · Answer

Explanation

3. The author suggests which of the following about the findings of information theorists?

Difficulty Level:   700

Explanation

(A) Their findings provocatively challenge the standard explanation of redundancy in genes.

No! mentioned in the passage the challenge. Instead, they help to have more insights

(B) Their findings provide useful insights into understanding the rationing of genetic information.

Correct. The sentence above illustrates just this.

(C) Their findings help to explain why imprecision can occur in neural development but not why gross mistakes can occur.

No. Neither they know why we do have gross mistakes

(D) Their findings suggest that genes may be able to specify neural development more accurately than had previously been thought.

No! mentioned in the passage

(E) Their findings support the work of those who use computer operations as models for understanding genetic control.

Out of scope

Answer: B

Sajjad1994 · Answer

Explanation

7. Which of the following can be inferred from the passage about the genetic information of Daphniae?

Difficulty Level:   700

Explanation

I.  It is universally accepted among information theorists that codes and languages can be made mistake-resistant by incorporating redundancy

I is correct

II.  the more precisely a system is specified, using a given limited amount of information, the greater the danger of gross mistakes.

II is incorrect

III.  However, since the amount of space available in any information system is limited, increased redundancy results in decreased precision.

III says the exact contrary, so is wrong

Answer: A

Prerana94 · Answer

1. Which of the following best expresses the main idea of the passage?

(A) Although studies of isogenic organisms have shown that all organisms are subject to developmental variations, there is still scientific debate over the exact causes of these variations.
(B) Because of limitations on the amount of information contained in the genes of organisms, developing nervous systems are subject to two basic kinds of error, the likelihood of one of which is reduced only when the likelihood of the other is increased.
(C) The complexity of an organism's genetic information means that much of the unusual variation that occurs among organisms can best be explained as the result of developmental mistakes.
(D) New findings about the nature of the genetic control of neural development support the work of; some scientists who argue that the computer is an extremely useful model for understanding the nervous system.
(E) The major discovery made by scientists studying the genetic control of neural

What is wrong with option 'C'? overall it wants to say that unusual variation is due to development mistakes. paragraph 3 states the technicality of it. Please explain.  Sajjad1994  . Is it the first part? complexity of genetic information because of which this option is incorrect?

Sajjad1994 · Answer

For this particular passage one needs to connect information given in the first paragraph with the information given at the end of the passage. Paragraph 1 starts the debate and the paragraph concludes it. In option C the information from the first paragraph is missing and the info from the last paragraph is mispresented. Compare (C) with (B)

(C) The  complexity  of an organism's genetic information means that much of the  unusual variation  that occurs among organisms  can best be explained as the result of developmental mistakes.

(B)  Because of limitations on the amount of information contained in the genes of organisms   , developing nervous systems are subject to two basic kinds of error,   the likelihood of one of which is reduced only when the likelihood of the other is increased.

So option (B) failed to capture the core of the passage while option (B) carries all the paragraphs. And hence (B) is the winner.

GTLH · Answer

How is the difficulty of this passage at 505-605 level....

Bunuel · Answer

The difficulty level of a question on the site, after sufficient attempts, is determined automatically based on various parameters collected from users' attempts via timer, such as the percentage of correct answers and the time taken to answer the question. So, this is a 505-605 Level question based on our statistics.

glagad · Answer

This was indeed a tough passage for me. Had to re-read the entire passage twice.

The more that is discovered about the intricate organization of the ne

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The more that is discovered about the intricate organization of the ne

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