Evolution and Mutations - GRE Subject Test: Biology
Card 0 of 120
Which structures did not evolve after plants emerged onto land?
Which structures did not evolve after plants emerged onto land?
Cell walls were present in plant cells before the transition to land. Seeds, stomata, waxy cuticles, and vascular transport all evolved to reduce water loss and circulate water to all areas of the plant. Water loss and circulation were not an issue before the transition to land; plants were forced to adapt these traits in order to survive in a terrestrial environment.
Cell walls were present in plant cells before the transition to land. Seeds, stomata, waxy cuticles, and vascular transport all evolved to reduce water loss and circulate water to all areas of the plant. Water loss and circulation were not an issue before the transition to land; plants were forced to adapt these traits in order to survive in a terrestrial environment.
Compare your answer with the correct one above
Which is not a necessary condition for the Hardy-Weinberg equation to be true?
Which is not a necessary condition for the Hardy-Weinberg equation to be true?
For the Hardy-Weinberg equation to be true, the population in question must be very large. This ensures that coincidental occurrences do not drastically alter allelic frequencies.
For the Hardy-Weinberg equation to be true, the population in question must be very large. This ensures that coincidental occurrences do not drastically alter allelic frequencies.
Compare your answer with the correct one above
What term best describes when one species exhibits two or more defined phenotypes within the same population?
What term best describes when one species exhibits two or more defined phenotypes within the same population?
The correct answer is polymorphism. A polymorphism refers to multiple phenoytpes (morphs) that exist within a population, generally as a result of multiple alleles for the same gene.
Sympatry and allopatry refer to mechanisms of speciation and natural selection favors a certain phenotype for its fitness or other survival advantages. Assortative mating describes a biased mating pattern based on either phenotype or behavior.
The correct answer is polymorphism. A polymorphism refers to multiple phenoytpes (morphs) that exist within a population, generally as a result of multiple alleles for the same gene.
Sympatry and allopatry refer to mechanisms of speciation and natural selection favors a certain phenotype for its fitness or other survival advantages. Assortative mating describes a biased mating pattern based on either phenotype or behavior.
Compare your answer with the correct one above
Which of the following is most accurate about single nucleotide polymorphisms (SNPs)?
Which of the following is most accurate about single nucleotide polymorphisms (SNPs)?
In order for a nucleotide substitution to be considered a SNP and not a random mutation, it must occur in 1% or more of the population. SNPs are more frequently found in non-coding regions. Typically, SNPs are much less commonly found in AT-rich microsatellites.
In order for a nucleotide substitution to be considered a SNP and not a random mutation, it must occur in 1% or more of the population. SNPs are more frequently found in non-coding regions. Typically, SNPs are much less commonly found in AT-rich microsatellites.
Compare your answer with the correct one above
What is the major difference between synonymous and non-synonymous substitutions?
What is the major difference between synonymous and non-synonymous substitutions?
If single nucleotide polymorphisms (SNPs) that occur in coding regions do not trigger an amino acid change in the protein, they are synonymous. A SNP can cause a missense mutation (an amino acid change in the protein) or a nonsense mutation (an amino acid change to a stop codon), both of these are nonsynonymous substitutions.
If single nucleotide polymorphisms (SNPs) that occur in coding regions do not trigger an amino acid change in the protein, they are synonymous. A SNP can cause a missense mutation (an amino acid change in the protein) or a nonsense mutation (an amino acid change to a stop codon), both of these are nonsynonymous substitutions.
Compare your answer with the correct one above
Which type of mutation creates a premature stop codon in the mRNA?
Which type of mutation creates a premature stop codon in the mRNA?
While a missense mutation involves substituting a base pair, resulting in a new amino acid, a nonsense mutation takes place when the new substituted codon is a stop codon. This causes the protein to stop being translated prematurely. Because of their impact on protein production, nonsense mutations very commonly prevent the formation of a functional protein.
Silent mutations result in no change in primary protein structure. Due to the degeneracy of the genetic code, a mutation can occur without changing the identity of the amino acid recruited during translation. A frameshift mutation results in a shift in the codon reading frame, severely altering the primary protein structure and often resulting in a truncated protein.
While a missense mutation involves substituting a base pair, resulting in a new amino acid, a nonsense mutation takes place when the new substituted codon is a stop codon. This causes the protein to stop being translated prematurely. Because of their impact on protein production, nonsense mutations very commonly prevent the formation of a functional protein.
Silent mutations result in no change in primary protein structure. Due to the degeneracy of the genetic code, a mutation can occur without changing the identity of the amino acid recruited during translation. A frameshift mutation results in a shift in the codon reading frame, severely altering the primary protein structure and often resulting in a truncated protein.
Compare your answer with the correct one above
A __________ mutation always results in the ribosome encountering a premature stop codon.
A __________ mutation always results in the ribosome encountering a premature stop codon.
Nonsense mutations are the name specifically given to mutations that cause the ribosome to encounter a premature stop codon and terminate translation early. A point mutation causes the transcription of a stop codon by changing the DNA transcript transcribe to the mRNA stop codons UAG, UAA, or UGA. Placement of this codon in the transcript will interrupt translation.
Missense mutations are a type of mutation that result in the inclusion of a different amino acid than the wild type protein. Frameshift mutations result in a change to the codon reading frame, and are typically caused by deletion or insertion mutations. Frameshift mutations have the most dramatic and detrimental effect on proteins. Deletion mutations result from removal of one or more base pairs.
Nonsense mutations are the name specifically given to mutations that cause the ribosome to encounter a premature stop codon and terminate translation early. A point mutation causes the transcription of a stop codon by changing the DNA transcript transcribe to the mRNA stop codons UAG, UAA, or UGA. Placement of this codon in the transcript will interrupt translation.
Missense mutations are a type of mutation that result in the inclusion of a different amino acid than the wild type protein. Frameshift mutations result in a change to the codon reading frame, and are typically caused by deletion or insertion mutations. Frameshift mutations have the most dramatic and detrimental effect on proteins. Deletion mutations result from removal of one or more base pairs.
Compare your answer with the correct one above
Sickle cell anemia is a disorder caused by the alteration of one amino acid in hemoglobin. Based on this, what kind of mutation causes sickle cell anemia?
Sickle cell anemia is a disorder caused by the alteration of one amino acid in hemoglobin. Based on this, what kind of mutation causes sickle cell anemia?
When only one amino acid is changed in a polypeptide, it is commonly caused by a point mutation, where one base pair has been changed. Silent, missense, and nonsense mutations can all be caused by a point mutation. Since the amino acid sequence has been changed, this is an example of a missense mutation. A silent mutation would not change the amino acid sequence, and a nonsense mutation would result in a premature stop codon during translation.
When only one amino acid is changed in a polypeptide, it is commonly caused by a point mutation, where one base pair has been changed. Silent, missense, and nonsense mutations can all be caused by a point mutation. Since the amino acid sequence has been changed, this is an example of a missense mutation. A silent mutation would not change the amino acid sequence, and a nonsense mutation would result in a premature stop codon during translation.
Compare your answer with the correct one above
Genetic drift is a phenomenon by which __________ in a population change.
Genetic drift is a phenomenon by which __________ in a population change.
Genetic drift specifically refers to the change of allele frequencies because of random sampling of gametes. Essentially, this induces genetic bias for particular alleles and can lead to speciation events simply by the chance event of certain gametes producing offspring rather than others.
Changes in mutation frequencies, random mating, and natural selection may lead to changes in allele frequencies, but they are not necessarily the cause of genetic drift.
Genetic drift specifically refers to the change of allele frequencies because of random sampling of gametes. Essentially, this induces genetic bias for particular alleles and can lead to speciation events simply by the chance event of certain gametes producing offspring rather than others.
Changes in mutation frequencies, random mating, and natural selection may lead to changes in allele frequencies, but they are not necessarily the cause of genetic drift.
Compare your answer with the correct one above
Which of the following factors plays the biggest role in the impact of genetic drift on a population?
Which of the following factors plays the biggest role in the impact of genetic drift on a population?
Genetic drift occurs when a gene's frequency is changed in a population due to pure chance. Consider a rock rolling down a hill and crushing all flowers that have white petals. The population will now have only red petals because the white ones were destroyed. Were the red petal flowers more suited to their environment? No, it just so happened that all of the white were removed from the gene pool. This shows that evolution can occur due to random chance as well as natural selection, and both forces can have an impact on a population.
Genetic drift occurs when a gene's frequency is changed in a population due to pure chance. Consider a rock rolling down a hill and crushing all flowers that have white petals. The population will now have only red petals because the white ones were destroyed. Were the red petal flowers more suited to their environment? No, it just so happened that all of the white were removed from the gene pool. This shows that evolution can occur due to random chance as well as natural selection, and both forces can have an impact on a population.
Compare your answer with the correct one above
A population is in Hardy-Weinberg equilibrium. The gene of interest has two alleles, with 16% of the population portraying the features of the recessive phenotype. What percentage of the population is heterozygous?
A population is in Hardy-Weinberg equilibrium. The gene of interest has two alleles, with 16% of the population portraying the features of the recessive phenotype. What percentage of the population is heterozygous?
Using the Hardy-Weinberg equilibrium equations, you can determine the answer.
The value of 
gives us the frequency of the dominant allele, while the value of 
gives us the frequency of the recessive allele. The second equation corresponds to genotypes. 
is the homozygous dominant frequency, 
is the heterozygous frequency, and 
is the homozygous recessive frequency.
16% of the population shows the recessive phenotype, and therefore must carry the homozygous recessive genotype. We can use this information to solve for the recessive allele frequency.
We can use the value of 
and the first Hardy-Weinberg equation to solve for 
.
Knowing both 
and 
, you can use the second equation to find the percent of heterozygous organisms in the population.
Using the Hardy-Weinberg equilibrium equations, you can determine the answer.
The value of
16% of the population shows the recessive phenotype, and therefore must carry the homozygous recessive genotype. We can use this information to solve for the recessive allele frequency.
We can use the value of
Knowing both
Compare your answer with the correct one above
In the Hardy-Weinberg equations, what quantities are represented by the variables 
and 
?
In the Hardy-Weinberg equations, what quantities are represented by the variables
The variables 
and 
are specifically referring to the allele frequencies of the dominant and the recessive allele in a population, respectively.
Expected genotype frequencies can be seen in the equation:
In this equation, 
represents the expected genotype frequency of homozygous dominant organisms, 
represents the expected frequency of heterozygous organisms, and 
represents the frequency of homozygous recessive organisms. These values are the expected frequencies in the population, based on the Hardy-Weinberg conditions and allele frequencies; they may not be the values actually observed. To get observed genotype and phenotype frequencies, more information about the size and makeup of the population would be needed.
The variables
Expected genotype frequencies can be seen in the equation:
In this equation,
Compare your answer with the correct one above
In a population that is in Hardy-Weinberg equilibrium, the frequency of homozygous dominant individuals is 0.36. What is the percentage of homozygous recessive individuals in the population?
In a population that is in Hardy-Weinberg equilibrium, the frequency of homozygous dominant individuals is 0.36. What is the percentage of homozygous recessive individuals in the population?
The two equations pertaining to Hardy-Weinberg equilibrium are:
In this second equation, each term refers to the frequency of a given genotype. 
is the homozygous dominant frequency, 
is the heterozygous frequency, and 
is the homozygous recessive frequency.
From the question, we know that:
We now know the dominant allele frequency. Using the other Hardy-Weinberg equation, we can find the recessive allele frequency:
Returning to our genotype frequency terms, we can use this recessive allele frequency to find the homozygous recessive frequency:
The two equations pertaining to Hardy-Weinberg equilibrium are:
In this second equation, each term refers to the frequency of a given genotype.
From the question, we know that:
We now know the dominant allele frequency. Using the other Hardy-Weinberg equation, we can find the recessive allele frequency:
Returning to our genotype frequency terms, we can use this recessive allele frequency to find the homozygous recessive frequency:
Compare your answer with the correct one above
Which of the following variables would not be observed in a population at Hardy-Weinberg equilibrium?
Which of the following variables would not be observed in a population at Hardy-Weinberg equilibrium?
Hardy Weinberg equilibrium has requirements that must be met by a population in order to confirm that evolution is not taking place:
1. The population must be large in number.
2. There can be no new mutations entering the population.
3. Immigration and emigration cannot change the allelic frequencies of the population.
4. Mating must be random.
5. Natural selection cannot be taking place.
Since it was said that females are selectively choosing which males they mate with, Hardy Weinberg equilibrium is being violated.
Hardy Weinberg equilibrium has requirements that must be met by a population in order to confirm that evolution is not taking place:
1. The population must be large in number.
2. There can be no new mutations entering the population.
3. Immigration and emigration cannot change the allelic frequencies of the population.
4. Mating must be random.
5. Natural selection cannot be taking place.
Since it was said that females are selectively choosing which males they mate with, Hardy Weinberg equilibrium is being violated.
Compare your answer with the correct one above
A population at Hardy-Weinberg equilibrium has two alleles for fur color: red and black. Assume black is dominant to red fur color. Of the animals in the population, 16 percent of the animals have red fur.
What percentage of the alleles in the population code for black fur?
A population at Hardy-Weinberg equilibrium has two alleles for fur color: red and black. Assume black is dominant to red fur color. Of the animals in the population, 16 percent of the animals have red fur.
What percentage of the alleles in the population code for black fur?
Since we know that the population is in Hardy-Weinberg equilibrium and that there are only two alleles, we can use the Hardy-Weinberg equation to solve this problem:
Lets say that 
represents the black allele, and 
represents the red allele. Since we know that red is recessive to black, only animals with two red alleles will be red. Fortunately, the 
portion of the equation is the only portion that deals with red animals (the other two variables are black: both homozygous dominant as well as heterozygous). This means that 
is equal to the frequency of red animals in the population:
Since we now know the frequency of the red allele in the population, we simply subtract it from one in order to find the frequency of the black allele, which turns out to be 0.6.
Since we know that the population is in Hardy-Weinberg equilibrium and that there are only two alleles, we can use the Hardy-Weinberg equation to solve this problem:
Lets say that
Since we now know the frequency of the red allele in the population, we simply subtract it from one in order to find the frequency of the black allele, which turns out to be 0.6.
Compare your answer with the correct one above
Which of the following is an example of natural selection?
I. Horses are bred for strength and endurance, and over time, the population of horses is more robust.
II. A late spring storm kills all the young plants in a region, but they are spared outside the storm zone.
III. Ancient ancestors of giraffes instinctively wanted to have longer necks to reach food higher in the trees, leading to the present appearance of giraffes.
IV. A flower that happens to be more attractive to pollinators is more likely to have reproductive success.
V. A mutation of a bacterium caused by exposure to ultraviolet light causes the originally red colonies to be yellow instead.
Which of the following is an example of natural selection?
I. Horses are bred for strength and endurance, and over time, the population of horses is more robust.
II. A late spring storm kills all the young plants in a region, but they are spared outside the storm zone.
III. Ancient ancestors of giraffes instinctively wanted to have longer necks to reach food higher in the trees, leading to the present appearance of giraffes.
IV. A flower that happens to be more attractive to pollinators is more likely to have reproductive success.
V. A mutation of a bacterium caused by exposure to ultraviolet light causes the originally red colonies to be yellow instead.
It is always difficult to rephrase "survival of the fittest" in some new, clever way. The flowers which BY CHANCE have developed a different color, pattern, or odor that better attracts pollinators are indeed more likely to experience reproductive success and pass on these genes to their offspring. Competing plants might do well for a while, but they are already disfavored, and further environmental changes may put them even more at risk (or have no effect, or again favor them over the presently more attractive plants).
The horse choice is an example of intentional breeding—artificial selection.
The storm option does not imply any condition in any of the plants which conferred an advantage against freezing to death, or even any difference between species of plants; it is more akin to a question about mass extinction than to one about evolution.
The giraffe choice relates to the Lamarckian fallacy of being able to pass on acquired characteristics; species that are more successful just plain "luck out" relative to environmental stresses.
The bacterial response discusses a mutation without likely survival implications for the bacterium.
It is always difficult to rephrase "survival of the fittest" in some new, clever way. The flowers which BY CHANCE have developed a different color, pattern, or odor that better attracts pollinators are indeed more likely to experience reproductive success and pass on these genes to their offspring. Competing plants might do well for a while, but they are already disfavored, and further environmental changes may put them even more at risk (or have no effect, or again favor them over the presently more attractive plants).
The horse choice is an example of intentional breeding—artificial selection.
The storm option does not imply any condition in any of the plants which conferred an advantage against freezing to death, or even any difference between species of plants; it is more akin to a question about mass extinction than to one about evolution.
The giraffe choice relates to the Lamarckian fallacy of being able to pass on acquired characteristics; species that are more successful just plain "luck out" relative to environmental stresses.
The bacterial response discusses a mutation without likely survival implications for the bacterium.
Compare your answer with the correct one above
Which of the following refers to speciation that occurs due to reproductive isolation in populations that occupy the same geographical area?
Which of the following refers to speciation that occurs due to reproductive isolation in populations that occupy the same geographical area?
The correct answer is sympatric speciation. Although rare, sympatric speciation occurs in populations that occupy the same geography, but still develop reproductive isolation. This isolation is generally driven by behavioral differences. Allopatric speciation occurs in biogeographically distinct populations. Parapatric speciation occurs when there is a small hybrid zone or overlap of two biogeographically distinct populations. Balancing selection refers to a mode of natural selection, not speciation.
The correct answer is sympatric speciation. Although rare, sympatric speciation occurs in populations that occupy the same geography, but still develop reproductive isolation. This isolation is generally driven by behavioral differences. Allopatric speciation occurs in biogeographically distinct populations. Parapatric speciation occurs when there is a small hybrid zone or overlap of two biogeographically distinct populations. Balancing selection refers to a mode of natural selection, not speciation.
Compare your answer with the correct one above
Vertebrates are evolutionarily adapted to terrestial life. Which one of the following adaptations is LEAST likely to contribute to this land-based predominance?
Vertebrates are evolutionarily adapted to terrestial life. Which one of the following adaptations is LEAST likely to contribute to this land-based predominance?
Vertebrates have adapted to terrestial living due to their ability to maintain water inside their bodies, despite no longer being immersed in water. The loop of Henle in the nephrons is designed to concentrate urine, reabsorbing water without unnecessarily excreting it. The longer the loops descend into the medulla, the more concentrated the urine becomes. Shorter loops would not concentrate urine as much, and thus would not contribute to a vertebrate's adaptation to land-based life.
Internal lungs, impermeable skin, and internal fertilization would all protect vital processes from interference by the external environment.
Vertebrates have adapted to terrestial living due to their ability to maintain water inside their bodies, despite no longer being immersed in water. The loop of Henle in the nephrons is designed to concentrate urine, reabsorbing water without unnecessarily excreting it. The longer the loops descend into the medulla, the more concentrated the urine becomes. Shorter loops would not concentrate urine as much, and thus would not contribute to a vertebrate's adaptation to land-based life.
Internal lungs, impermeable skin, and internal fertilization would all protect vital processes from interference by the external environment.
Compare your answer with the correct one above
Members of a species of red fox have teeth of varying sharpness. Foxes with very sharp teeth are able to kill large prey for food, while foxes with very dull, strong teeth are able to crush eggs and small animals. Foxes with teeth of medium sharpness, however, cannot get food and many die before they are able to reproduce. Over time, the fox population shows a greater proportion of individuals with either very sharp or very dull teeth. Which type of natural selection best describes this situation?
Members of a species of red fox have teeth of varying sharpness. Foxes with very sharp teeth are able to kill large prey for food, while foxes with very dull, strong teeth are able to crush eggs and small animals. Foxes with teeth of medium sharpness, however, cannot get food and many die before they are able to reproduce. Over time, the fox population shows a greater proportion of individuals with either very sharp or very dull teeth. Which type of natural selection best describes this situation?
In this scenario, the two extreme phenotypes are selected for, while intermediate phenotypes are selected against. This is disruptive natural selection. Over time, disruptive selection results in a decreased frequency of "middle" phenotypes and an increased frequency of the two groups at the extreme ends. This is a process that can eventually lead to speciation.
The opposite is process stabilizing selection, in which the extreme variations are selected against in favor of more "average" phenotypes. Directional selection occurs when only one end of the spectrum is favored, such as sharp teeth but not dull teeth. Artificial selection involves human intervention in selecting desirable traits. Vestigial selection is not a type of natural selection.
In this scenario, the two extreme phenotypes are selected for, while intermediate phenotypes are selected against. This is disruptive natural selection. Over time, disruptive selection results in a decreased frequency of "middle" phenotypes and an increased frequency of the two groups at the extreme ends. This is a process that can eventually lead to speciation.
The opposite is process stabilizing selection, in which the extreme variations are selected against in favor of more "average" phenotypes. Directional selection occurs when only one end of the spectrum is favored, such as sharp teeth but not dull teeth. Artificial selection involves human intervention in selecting desirable traits. Vestigial selection is not a type of natural selection.
Compare your answer with the correct one above
In a certain species of feline, all males are much larger than females. Members of either sex that are of intermediate size struggle to find mates. What principle best describes this phenomenon?
In a certain species of feline, all males are much larger than females. Members of either sex that are of intermediate size struggle to find mates. What principle best describes this phenomenon?
Large size is favored in males and small size is favored in females, but intermediate size is always disfavored. The result is an increase in the two extreme phenotypes (either large or small) and a decrease in the average phenotype. This type of trend is known as disruptive selection.
Stabilizing selection occurs when the extreme phenotypes are disfavored, and the average or intermediate phenotype is preferable. Directional selection occurs when only one extreme phenotype is advantageous, for example if only large felines were able to find mates. Genetic drift is the phenomenon by which the allele frequencies of a population change by chance, due to independent assortment or other random events. The bottleneck effect occurs when an outside event, such as disease or natural disaster, diminishes the original population such that the allele frequencies of the new population differ from those of the original.
Large size is favored in males and small size is favored in females, but intermediate size is always disfavored. The result is an increase in the two extreme phenotypes (either large or small) and a decrease in the average phenotype. This type of trend is known as disruptive selection.
Stabilizing selection occurs when the extreme phenotypes are disfavored, and the average or intermediate phenotype is preferable. Directional selection occurs when only one extreme phenotype is advantageous, for example if only large felines were able to find mates. Genetic drift is the phenomenon by which the allele frequencies of a population change by chance, due to independent assortment or other random events. The bottleneck effect occurs when an outside event, such as disease or natural disaster, diminishes the original population such that the allele frequencies of the new population differ from those of the original.
Compare your answer with the correct one above