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Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and  lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs  forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings,  and human hands .  They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA – just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates ("fish") to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence  that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaalik’s limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture. 
The primary purpose of the passage is 
  • a)
    To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.
  • b)
    To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.
  • c)
    To trace the importance of the discovery of Tiktaalik.
  • d)
    To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.
  • e)
    To deduce how limbs of various sizes and shapes are built by the ZPA tissue.
Correct answer is option 'A'. Can you explain this answer?
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Directions: Read the Passage carefully and answer the question as follow.Through the glamour of the Colonial era, we are forced to acknowledge the classic charm shown in late seventeenth and early eighteenth century window designs. Developed as they were by American carpenters who were stimulated by remembrance of their early impressions of English architecture received in the mother land, there is no precise or spiritless copy of English details; rather there is expressed a vitality that has been brought out by earnest effort to reproduce the spirit desired. Undoubtedly, the lasting success of early American craftsmanship has been due to the perfect treatment of proportions, as related one to the other. That these are not imitations is proved by an occasional clumsiness which would be impossible, if they were exact copies of their more highly refined English prototypes.The grasp of the builder’s mind is vividly revealed in the construction of these windows for, while blunders are often made, successes are much more frequent. They are evolved from remembered motives that have been unified and balanced, that they might accord with the exterior and be knitted successfully into the interior trim. Some of these windows still grace seventeenth century houses, and are found not only on old southern plantations, but all through New England, especially along the sea coast. True products are they of Colonial craftsmanship, brought into existence by skilled artisans who have performed their work so perfectly that today they are found unimpaired, striking a dominant note in accord with the architectural feeling of the period.There is no question that windows such as these lend character to any house, provided, of course, that they coincide with the period. Doubtless, the designing of modified Colonial houses is responsible, in part, for the present-day revival of interest, not solely in windows of the Colonial period, but also in that which immediately preceded and followed it.Q. Which of the following would the author of the passage NOT agree with?

Directions: Read the Passage carefully and answer the question as follow.Through the glamour of the Colonial era, we are forced to acknowledge the classic charm shown in late seventeenth and early eighteenth century window designs. Developed as they were by American carpenters who were stimulated by remembrance of their early impressions of English architecture received in the mother land, there is no precise or spiritless copy of English details; rather there is expressed a vitality that has been brought out by earnest effort to reproduce the spirit desired. Undoubtedly, the lasting success of early American craftsmanship has been due to the perfect treatment of proportions, as related one to the other. That these are not imitations is proved by an occasional clumsiness which would be impossible, if they were exact copies of their more highly refined English prototypes.The grasp of the builder’s mind is vividly revealed in the construction of these windows for, while blunders are often made, successes are much more frequent. They are evolved from remembered motives that have been unified and balanced, that they might accord with the exterior and be knitted successfully into the interior trim. Some of these windows still grace seventeenth century houses, and are found not only on old southern plantations, but all through New England, especially along the sea coast. True products are they of Colonial craftsmanship, brought into existence by skilled artisans who have performed their work so perfectly that today they are found unimpaired, striking a dominant note in accord with the architectural feeling of the period.There is no question that windows such as these lend character to any house, provided, of course, that they coincide with the period. Doubtless, the designing of modified Colonial houses is responsible, in part, for the present-day revival of interest, not solely in windows of the Colonial period, but also in that which immediately preceded and followed it.Q.According to the information in the passage, which of these could be a characteristic of American colonial windows?

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Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer?
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Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer? for GMAT 2024 is part of GMAT preparation. The Question and answers have been prepared according to the GMAT exam syllabus. Information about Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer? covers all topics & solutions for GMAT 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer?.
Solutions for Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer? in English & in Hindi are available as part of our courses for GMAT. Download more important topics, notes, lectures and mock test series for GMAT Exam by signing up for free.
Here you can find the meaning of Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer?, a detailed solution for Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer? has been provided alongside types of Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice Despite radical differences in what limbs do and what they look like, the underlying blueprint of all limbs in land based animals, whether those limbs are wings in birds, flippers in penguins, or hands in humans, is the same - one bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes. Want to make a bat wing? Make the fingers really long. Want to make a horse? Elongate the middle fingers and toes and lose the outer ones. The differences between creatures lie in differences in the shapes and sizes of the bones and the numbers of blobs, fingers, and toes.In the 1950s and 1960s a number of biologists, including Edgar Zwilling and John Saunders, did extraordinarily creative experiments on chicken eggs to understand how skeletal structure of limbs forms and uncovered some of the key mechanisms that build limbs that have the same architecture but are as different as bird wings, lizards webbings, and human hands . They discovered that two little patches of tissue essentially control the development of the pattern of bones inside limbs. These patches of tissue were named the zone of polarizing activity (ZPA). The cells in the ZPA made special molecules that then spread across the limb to instruct cells to make femur, articulates, and connecting toes. The concentration of these molecules was the important factor and decided the length of femur, articulates, connecting toes, and even the length of individual toe fingers. Later experiments with other animals such as the bat, frog, etc. proved that the mechanism to form limbs remained the same - formation of limbs in every creature was controlled by the ZPA just the concentration of these special molecules varied corresponding to the desired structure.The reason for this inherent commonality in architecture still remained a conundrum for decades. Why did nature not develop architectures better optimized to the functional needs of various organisms? The discovery of Tiktaalik, a transition between non-tetrapod vertebrates (fish) to early tetrapods solved this mystery, providing evidence that all land based creatures that have limbs, hands, etc. share a common ancestor. The fact that our DNA and that of all land based animals can be traced back to Tiktaalik further provided evidence that all appendages, whether they are hands or limbs, are built by similar kinds of genes and that this great evolutionary transformation did not involve the origin of new DNA: much of the shift likely involved using ancient genes, such as those involved in development of Tiktaaliks limbs, in new ways to make wings in birds or various sized limbs with fingers and toes, explaining the diversity in shapes while maintaining the similarity in architecture.The primary purpose of the passage isa)To explain the reasons for the similarity in the architecture of the limbs of all land based organisms.b)To evaluate the implications of the experiments of Edgar Zwilling and John Saunders.c)To trace the importance of the discovery of Tiktaalik.d)To describe the role a common DNA plays in the unified architecture of the limbs of all land based organisms.e)To deduce how limbs of various sizes and shapes are built by the ZPA tissue.Correct answer is option 'A'. 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