Test: Reading Comprehension: Bio Sciences - GMAT MCQ

A team of researchers has been able to successfully study the highly complex molecular structure of mitoribosomes, which are the ribosomes of mitochondria. Ribosomes are found in the cells of all living organisms, and they serve as a primary location for biological protein synthesis, but certain organisms such as fungi, plants, animals, and humans contain much more complex ribosomes than bacteria do. In organisms with complex cells, ribosomes can also be divided into two types: those in the cytosol -- which comprises the majority of the cell -- and those found in the mitochondria or "power houses" of cells. Mitochondria are found only in eukaryotes. Every ribosome consists of two subunits. The smaller subunit uses transfer ribonucleic acids to decode the genetic code, which is stored in the DNA, it receives in the form of messenger ribonucleic acids, while the larger subunit joins the amino acids delivered by the transfer ribonucleic acids together like a string of pearls. 

Since they are found only in small amounts and are difficult to isolate, mitochondrial ribosomes or mitoribosomes are particularly difficult to study.  But because of the recent technical advances in cryo-electron microscopy and the development of direct electron detection cameras that can correct for specimen motion during the exposure, it recently became possible to capture images of biomolecules at a resolution high enough to capture the details, especially those of the peptidyl transferase centre (PTC).

This research is of special importance to producing the right kind of antibiotics for humans. PTC is where the amino acid building blocks are combined, leading to protein synthesis. As per the researchers, this process of synthesizing proteins is medically relevant as the tunnel through which the proteins pass, after being synthesized, is a target for specific antibiotics. The antibiotic blocks the tunnel, preventing the proteins that have just been synthesized from leaving the tunnel. However, for an antibiotic to be used in humans, it must not attack human ribosomes and should inhibit protein synthesis only in the ribosomes of bacteria.  The problem arises since mitochondrial ribosomes resemble those of bacteria, which is why certain antibiotics also interfere with mitoribosomes, possibly leading to serious side effects. The findings of the research will make it possible in the future to design antibiotics that inhibit only bacterial and not mitochondrial ribosomes, the one basic requirement for using them in clinical applications.

Which of the following most aptly describes the function of the first paragraph?

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. 

According to the passage the mechanism that builds limbs as different as bird wings, penguin flippers, and human hands etc. is 

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. 

In the context of the passage, why was the discovery of the Tiktaalik important? 

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. 

From the passage, what can be inferred about the architecture of limbs?

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 

Tit-for-Tat – a strategy that is a variation of an eye for an eye and a tooth for a tooth - is clear and simple, never initiates cheating, and provocable that it is, it never allows cheating to go unpunished.  It is surprisingly successful in two-person prisoner’s dilemma games. In a tournament that pitched 150 game theorists from around the world and in which contestants were ranked by the sum of their scores, the winner Anatol Rapoport successfully deployed this strategy. The result and the winner remained the same when the same tournament was repeated with an expanded audience.  One of the impressive features about Tit-for-Tat is that it did so well overall, even though it did not (nor could it) beat any one of its rivals in a head-on. At best, Tit-for-Tat ties its rivals. Hence, if the competition was scored as a winner take-all contest, Anatol would not have won. The two advantages of Tit-for-Tat are that firstly, it always comes close and secondly, it usually encourages cooperation while avoiding exploitation.

In-spite of the above, Tit-for-Tat is a flawed strategy in certain situations. The slightest possibility of misperception results in the complete breakdown in the success of Tit-for-Tat. For example, in 1987, the United States responded to the Soviet spying and wiretapping of the US embassy in Moscow by reducing the number of Soviet diplomats permitted in United States. The Soviets responded by cutting the support staff at the US embassy in Moscow and reducing the number of US diplomats. As a result, both countries found it difficult to carry on their diplomatic functions.  The problem with Tit-for-Tat is that any mistake echoes back and forth and sets up a chain reaction that has the potential to cause grave damage.

The passage suggests that Anatol Rapoport won the two-person prisoner’s dilemma tournaments because

Tit-for-Tat – a strategy that is a variation of an eye for an eye and a tooth for a tooth - is clear and simple, never initiates cheating, and provocable that it is, it never allows cheating to go unpunished.  It is surprisingly successful in two-person prisoner’s dilemma games. In a tournament that pitched 150 game theorists from around the world and in which contestants were ranked by the sum of their scores, the winner Anatol Rapoport successfully deployed this strategy. The result and the winner remained the same when the same tournament was repeated with an expanded audience.  One of the impressive features about Tit-for-Tat is that it did so well overall, even though it did not (nor could it) beat any one of its rivals in a head-on. At best, Tit-for-Tat ties its rivals. Hence, if the competition was scored as a winner take-all contest, Anatol would not have won. The two advantages of Tit-for-Tat are that firstly, it always comes close and secondly, it usually encourages cooperation while avoiding exploitation.

In-spite of the above, Tit-for-Tat is a flawed strategy in certain situations. The slightest possibility of misperception results in the complete breakdown in the success of Tit-for-Tat. For example, in 1987, the United States responded to the Soviet spying and wiretapping of the US embassy in Moscow by reducing the number of Soviet diplomats permitted in United States. The Soviets responded by cutting the support staff at the US embassy in Moscow and reducing the number of US diplomats. As a result, both countries found it difficult to carry on their diplomatic functions.  The problem with Tit-for-Tat is that any mistake echoes back and forth and sets up a chain reaction that has the potential to cause grave damage.

What can be inferred about the two-person prisoner’s dilemma tournaments discussed in the passage?

Tit-for-Tat – a strategy that is a variation of an eye for an eye and a tooth for a tooth - is clear and simple, never initiates cheating, and provocable that it is, it never allows cheating to go unpunished.  It is surprisingly successful in two-person prisoner’s dilemma games. In a tournament that pitched 150 game theorists from around the world and in which contestants were ranked by the sum of their scores, the winner Anatol Rapoport successfully deployed this strategy. The result and the winner remained the same when the same tournament was repeated with an expanded audience.  One of the impressive features about Tit-for-Tat is that it did so well overall, even though it did not (nor could it) beat any one of its rivals in a head-on. At best, Tit-for-Tat ties its rivals. Hence, if the competition was scored as a winner take-all contest, Anatol would not have won. The two advantages of Tit-for-Tat are that firstly, it always comes close and secondly, it usually encourages cooperation while avoiding exploitation.

In-spite of the above, Tit-for-Tat is a flawed strategy in certain situations. The slightest possibility of misperception results in the complete breakdown in the success of Tit-for-Tat. For example, in 1987, the United States responded to the Soviet spying and wiretapping of the US embassy in Moscow by reducing the number of Soviet diplomats permitted in United States. The Soviets responded by cutting the support staff at the US embassy in Moscow and reducing the number of US diplomats. As a result, both countries found it difficult to carry on their diplomatic functions.  The problem with Tit-for-Tat is that any mistake echoes back and forth and sets up a chain reaction that has the potential to cause grave damage.

What can be inferred about the two-person prisoner’s dilemma tournaments discussed in the passage?

Tit-for-Tat – a strategy that is a variation of an eye for an eye and a tooth for a tooth - is clear and simple, never initiates cheating, and provocable that it is, it never allows cheating to go unpunished.  It is surprisingly successful in two-person prisoner’s dilemma games. In a tournament that pitched 150 game theorists from around the world and in which contestants were ranked by the sum of their scores, the winner Anatol Rapoport successfully deployed this strategy. The result and the winner remained the same when the same tournament was repeated with an expanded audience.  One of the impressive features about Tit-for-Tat is that it did so well overall, even though it did not (nor could it) beat any one of its rivals in a head-on. At best, Tit-for-Tat ties its rivals. Hence, if the competition was scored as a winner take-all contest, Anatol would not have won. The two advantages of Tit-for-Tat are that firstly, it always comes close and secondly, it usually encourages cooperation while avoiding exploitation.

In-spite of the above, Tit-for-Tat is a flawed strategy in certain situations. The slightest possibility of misperception results in the complete breakdown in the success of Tit-for-Tat. For example, in 1987, the United States responded to the Soviet spying and wiretapping of the US embassy in Moscow by reducing the number of Soviet diplomats permitted in United States. The Soviets responded by cutting the support staff at the US embassy in Moscow and reducing the number of US diplomats. As a result, both countries found it difficult to carry on their diplomatic functions.  The problem with Tit-for-Tat is that any mistake echoes back and forth and sets up a chain reaction that has the potential to cause grave damage.

According to the passage, the reason why both US and Soviet embassies found it difficult to carry on their diplomatic functions is

Sea turtles, reptilian amphibians that are classified into seven distinct sub-species, are quickly beginning to rank among some of the most endangered species on the planet. These ancient reptiles are vital to Earth’s ecosystem because they feed on botanical life that grows on sea beds and thereby help maintain the natural habitat of several other marine life forms. Further, unhatched sea turtle eggs provide nutrients for plants that grow beneath the surface of the sea, which in turn strengthen sand dunes through their root systems and help prevent beaches from eroding.

Ironically, human attempts to preserve the marine environment in which sea turtles live are causing the species’ numbers to dwindle even faster. In an effort to protect sea turtles that nest on the beaches,  in some popular fishing areas local authorities have placed restrictions on the amount of fishing in order to protect the turtles from being caught in fishing nets and drowning. However, the reduction in the amount of fishing in these areas has led to an increase in the numbers of the giant cuttlefish, which feed on the same underwater plants as the sea turtles do. The subsequent decrease in the turtles’ food source, particularly the sea grass that is part of the turtles’ staple diet, has not only led to an alarming reduction in the number of sea turtles in these areas but also affected the balance of the marine ecosystem in these regions.The passage is primarily concerned with

Sea turtles, reptilian amphibians that are classified into seven distinct sub-species, are quickly beginning to rank among some of the most endangered species on the planet. These ancient reptiles are vital to Earth’s ecosystem because they feed on botanical life that grows on sea beds and thereby help maintain the natural habitat of several other marine life forms. Further, unhatched sea turtle eggs provide nutrients for plants that grow beneath the surface of the sea, which in turn strengthen sand dunes through their root systems and help prevent beaches from eroding.

Ironically, human attempts to preserve the marine environment in which sea turtles live are causing the species’ numbers to dwindle even faster. In an effort to protect sea turtles that nest on the beaches,  in some popular fishing areas local authorities have placed restrictions on the amount of fishing in order to protect the turtles from being caught in fishing nets and drowning. However, the reduction in the amount of fishing in these areas has led to an increase in the numbers of the giant cuttlefish, which feed on the same underwater plants as the sea turtles do. The subsequent decrease in the turtles’ food source, particularly the sea grass that is part of the turtles’ staple diet, has not only led to an alarming reduction in the number of sea turtles in these areas but also affected the balance of the marine ecosystem in these regions.

The author suggests which of the following about sea turtles?

Sea turtles, reptilian amphibians that are classified into seven distinct sub-species, are quickly beginning to rank among some of the most endangered species on the planet. These ancient reptiles are vital to Earth’s ecosystem because they feed on botanical life that grows on sea beds and thereby help maintain the natural habitat of several other marine life forms. Further, unhatched sea turtle eggs provide nutrients for plants that grow beneath the surface of the sea, which in turn strengthen sand dunes through their root systems and help prevent beaches from eroding.

Ironically, human attempts to preserve the marine environment in which sea turtles live are causing the species’ numbers to dwindle even faster. In an effort to protect sea turtles that nest on the beaches,  in some popular fishing areas local authorities have placed restrictions on the amount of fishing in order to protect the turtles from being caught in fishing nets and drowning. However, the reduction in the amount of fishing in these areas has led to an increase in the numbers of the giant cuttlefish, which feed on the same underwater plants as the sea turtles do. The subsequent decrease in the turtles’ food source, particularly the sea grass that is part of the turtles’ staple diet, has not only led to an alarming reduction in the number of sea turtles in these areas but also affected the balance of the marine ecosystem in these regions.Which of the following CANNOT be inferred from the passage?

Sea turtles, reptilian amphibians that are classified into seven distinct sub-species, are quickly beginning to rank among some of the most endangered species on the planet. These ancient reptiles are vital to Earth’s ecosystem because they feed on botanical life that grows on sea beds and thereby help maintain the natural habitat of several other marine life forms. Further, unhatched sea turtle eggs provide nutrients for plants that grow beneath the surface of the sea, which in turn strengthen sand dunes through their root systems and help prevent beaches from eroding.

Ironically, human attempts to preserve the marine environment in which sea turtles live are causing the species’ numbers to dwindle even faster. In an effort to protect sea turtles that nest on the beaches,  in some popular fishing areas local authorities have placed restrictions on the amount of fishing in order to protect the turtles from being caught in fishing nets and drowning. However, the reduction in the amount of fishing in these areas has led to an increase in the numbers of the giant cuttlefish, which feed on the same underwater plants as the sea turtles do. The subsequent decrease in the turtles’ food source, particularly the sea grass that is part of the turtles’ staple diet, has not only led to an alarming reduction in the number of sea turtles in these areas but also affected the balance of the marine ecosystem in these regions.

The author refers to the giant cuttlefish in order to

This much was well known that the purpose of a gene is to store the recipe for making proteins and that we inherit from our parents a gigantic list of recipes for making proteins and protein-making machines.  What was not clear as late as the early 20th century until Gregor Mendel’s experiments were published and understood was that when crossed, the expression of these genes skipped a generation.

Mendel discovered that when white flower and purple flower plants are crossed, the result is not a blend. Rather than being a mix of the two, the offspring was purple flowered. He then conceived the idea of heredity units, which he called "factors", one of which is a recessive characteristic and the other dominant. Mendel said that factors, later called genes, normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. The dominant gene, such as the purple flower in Mendel's plants, will hide the recessive gene, the white flower. Mendel crossed over 29,000 plants including inflated seed pods with wrinkled seed pods, green unripe pods with yellow unripe pods, and axial flowers with terminal flowers. In every case the resulting hybrids were just like one parent with the essence of other parent missing. However, as these hybrids were allowed to self-fertilize, the essence of the recessed parent re-appeared in exactly one third of the cases. This re-appearance is called the law of thirds. This law is not just obeyed in plants but also in every living species as demonstrated by Nageli’s experiment on crossing angora cats with another breed. Nageli observed that the angora coat disappeared in the next generation but re-appeared in the kittens in the third. 

Mendel’s law has been put to a variety of uses such as selecting the right plants to hybridize to get the desired mix of dominant factors. A surprising use of the law has been to explain Alkaptonuria in which the patients suffered from arthritis and their urine and the ear wax turned reddish black upon exposure to air. Rare in the general population but frequent in children of first-cousin marriages, the incidence of Alkaptonuria is attributed to expression of recessive factors.

According to the passage, all of the following about Mendel’s dominant factors are true except 

This much was well known that the purpose of a gene is to store the recipe for making proteins and that we inherit from our parents a gigantic list of recipes for making proteins and protein-making machines.  What was not clear as late as the early 20th century until Gregor Mendel’s experiments were published and understood was that when crossed, the expression of these genes skipped a generation.

Mendel discovered that when white flower and purple flower plants are crossed, the result is not a blend. Rather than being a mix of the two, the offspring was purple flowered. He then conceived the idea of heredity units, which he called "factors", one of which is a recessive characteristic and the other dominant. Mendel said that factors, later called genes, normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. The dominant gene, such as the purple flower in Mendel's plants, will hide the recessive gene, the white flower. Mendel crossed over 29,000 plants including inflated seed pods with wrinkled seed pods, green unripe pods with yellow unripe pods, and axial flowers with terminal flowers. In every case the resulting hybrids were just like one parent with the essence of other parent missing. However, as these hybrids were allowed to self-fertilize, the essence of the recessed parent re-appeared in exactly one third of the cases. This re-appearance is called the law of thirds. This law is not just obeyed in plants but also in every living species as demonstrated by Nageli’s experiment on crossing angora cats with another breed. Nageli observed that the angora coat disappeared in the next generation but re-appeared in the kittens in the third. 

Mendel’s law has been put to a variety of uses such as selecting the right plants to hybridize to get the desired mix of dominant factors. A surprising use of the law has been to explain Alkaptonuria in which the patients suffered from arthritis and their urine and the ear wax turned reddish black upon exposure to air. Rare in the general population but frequent in children of first-cousin marriages, the incidence of Alkaptonuria is attributed to expression of recessive factors.

The author mentions Nageli’s experiment to illustrate 

This much was well known that the purpose of a gene is to store the recipe for making proteins and that we inherit from our parents a gigantic list of recipes for making proteins and protein-making machines.  What was not clear as late as the early 20th century until Gregor Mendel’s experiments were published and understood was that when crossed, the expression of these genes skipped a generation.

Mendel discovered that when white flower and purple flower plants are crossed, the result is not a blend. Rather than being a mix of the two, the offspring was purple flowered. He then conceived the idea of heredity units, which he called "factors", one of which is a recessive characteristic and the other dominant. Mendel said that factors, later called genes, normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. The dominant gene, such as the purple flower in Mendel's plants, will hide the recessive gene, the white flower. Mendel crossed over 29,000 plants including inflated seed pods with wrinkled seed pods, green unripe pods with yellow unripe pods, and axial flowers with terminal flowers. In every case the resulting hybrids were just like one parent with the essence of other parent missing. However, as these hybrids were allowed to self-fertilize, the essence of the recessed parent re-appeared in exactly one third of the cases. This re-appearance is called the law of thirds. This law is not just obeyed in plants but also in every living species as demonstrated by Nageli’s experiment on crossing angora cats with another breed. Nageli observed that the angora coat disappeared in the next generation but re-appeared in the kittens in the third. 

Mendel’s law has been put to a variety of uses such as selecting the right plants to hybridize to get the desired mix of dominant factors. A surprising use of the law has been to explain Alkaptonuria in which the patients suffered from arthritis and their urine and the ear wax turned reddish black upon exposure to air. Rare in the general population but frequent in children of first-cousin marriages, the incidence of Alkaptonuria is attributed to expression of recessive factors.

The primary purpose of the passage is to 

This much was well known that the purpose of a gene is to store the recipe for making proteins and that we inherit from our parents a gigantic list of recipes for making proteins and protein-making machines.  What was not clear as late as the early 20th century until Gregor Mendel’s experiments were published and understood was that when crossed, the expression of these genes skipped a generation.

Mendel discovered that when white flower and purple flower plants are crossed, the result is not a blend. Rather than being a mix of the two, the offspring was purple flowered. He then conceived the idea of heredity units, which he called "factors", one of which is a recessive characteristic and the other dominant. Mendel said that factors, later called genes, normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. The dominant gene, such as the purple flower in Mendel's plants, will hide the recessive gene, the white flower. Mendel crossed over 29,000 plants including inflated seed pods with wrinkled seed pods, green unripe pods with yellow unripe pods, and axial flowers with terminal flowers. In every case the resulting hybrids were just like one parent with the essence of other parent missing. However, as these hybrids were allowed to self-fertilize, the essence of the recessed parent re-appeared in exactly one third of the cases. This re-appearance is called the law of thirds. This law is not just obeyed in plants but also in every living species as demonstrated by Nageli’s experiment on crossing angora cats with another breed. Nageli observed that the angora coat disappeared in the next generation but re-appeared in the kittens in the third. 

Mendel’s law has been put to a variety of uses such as selecting the right plants to hybridize to get the desired mix of dominant factors. A surprising use of the law has been to explain Alkaptonuria in which the patients suffered from arthritis and their urine and the ear wax turned reddish black upon exposure to air. Rare in the general population but frequent in children of first-cousin marriages, the incidence of Alkaptonuria is attributed to expression of recessive factors.

According to the passage, which of the following is not true about genes?