Molecular Biology and Genetics - GRE
Card 0 of 756
What event is indicative of transcription initiation?
What event is indicative of transcription initiation?
During the initiation of transcription, RNA polymerase and a group of transcription factors bind to the promoter for a given gene. This DNA segment signals the RNA polymerase where to begin creating the RNA strand.
During the initiation of transcription, RNA polymerase and a group of transcription factors bind to the promoter for a given gene. This DNA segment signals the RNA polymerase where to begin creating the RNA strand.
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The 5' cap on eukaryotic mRNA molecules is recognized by which of the following proteins?
The 5' cap on eukaryotic mRNA molecules is recognized by which of the following proteins?
The 5' cap is recognized by the important translation factor eIF4e. Once bound, eIF4e helps transport the mRNA molecule to the ribosome and facilitates bonding to the ribosomal machinery.
The 3' poly-A tail is recognized by PABP. RNA polymerase is involved in transcription, not translation. The 40s ribosomal subunit is recruited by the initiation complex (including eIF4e, PABP, and various other translation factors).
The 5' cap is recognized by the important translation factor eIF4e. Once bound, eIF4e helps transport the mRNA molecule to the ribosome and facilitates bonding to the ribosomal machinery.
The 3' poly-A tail is recognized by PABP. RNA polymerase is involved in transcription, not translation. The 40s ribosomal subunit is recruited by the initiation complex (including eIF4e, PABP, and various other translation factors).
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Chloramphenicol prevents protein translation by which of the following mechanisms?
Chloramphenicol prevents protein translation by which of the following mechanisms?
Tetracycline blocks the binding of aminoacyl tRNA to the A site of the ribosome.
Cyclohexamide blocks the translocation reaction on ribosomes.
Rifamycin blocks the initiation of RNA chains by binding to RNA polymerase.
Chloramphenicol blocks the pepidyl transferase reaction on the ribosome.
Tetracycline blocks the binding of aminoacyl tRNA to the A site of the ribosome.
Cyclohexamide blocks the translocation reaction on ribosomes.
Rifamycin blocks the initiation of RNA chains by binding to RNA polymerase.
Chloramphenicol blocks the pepidyl transferase reaction on the ribosome.
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During translation, which site in the ribosome allows for tRNA moelcules to enter the complex?
During translation, which site in the ribosome allows for tRNA moelcules to enter the complex?
The ribosomal complex has three sites where tRNA moelcules can be oriented during the process of translation: the A site, the P site, and the E site. During polypeptide elongation, a tRNA with an attached amino acid will enter at the A site. It will then move to the P site, now holding the growing polypeptide chain. All tRNAs no longer holding an amino acid will exit the ribosome at the E site.
The ribosomal complex has three sites where tRNA moelcules can be oriented during the process of translation: the A site, the P site, and the E site. During polypeptide elongation, a tRNA with an attached amino acid will enter at the A site. It will then move to the P site, now holding the growing polypeptide chain. All tRNAs no longer holding an amino acid will exit the ribosome at the E site.
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On which of the following molecules could you find an anticodon?
On which of the following molecules could you find an anticodon?
In order to make sure that the proper amino acid is added to the growing polypeptide chain, an anticodon found on the tRNA carrying the amino acid must be a match for the codon found on the mRNA.
In order to make sure that the proper amino acid is added to the growing polypeptide chain, an anticodon found on the tRNA carrying the amino acid must be a match for the codon found on the mRNA.
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Each of the listed statements about transposable genetic elements in eukaryotic genomes are true except for which one?
Each of the listed statements about transposable genetic elements in eukaryotic genomes are true except for which one?
Transposable elements are divided into two categories: Type 1 (retrotransposons), which form RNA intermediates, and type 2 (transposons), which do not form RNA intermediates and directly enter a new site. Transposase proteins regulate the translocation of type 2 transposable elements, which do not require a RNA intermediate.
Transposable elements are divided into two categories: Type 1 (retrotransposons), which form RNA intermediates, and type 2 (transposons), which do not form RNA intermediates and directly enter a new site. Transposase proteins regulate the translocation of type 2 transposable elements, which do not require a RNA intermediate.
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What is the defining characteristic of temperate phage?
What is the defining characteristic of temperate phage?
Temperate phages a so named because after infecting a bacterial cell, they can enter either the lysogenic or lytic cycle. Other phages cannot enter the lysogenic cycle and will always enter the lytic one. Since they have the choice to either hide out in the cell unnoticed or immediately replicate and lyse the cell lysogenic phages are refereed to as temperate.
Temperate phages a so named because after infecting a bacterial cell, they can enter either the lysogenic or lytic cycle. Other phages cannot enter the lysogenic cycle and will always enter the lytic one. Since they have the choice to either hide out in the cell unnoticed or immediately replicate and lyse the cell lysogenic phages are refereed to as temperate.
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What is the physiological purpose of a tandem gene array?
What is the physiological purpose of a tandem gene array?
Tandem arrays are used for extremely important genes, like ribosomal RNA genes that are vital for organism function. The arrays serve to allow massive parallelized encoding of these genes, because many copies are required.
Tandem arrays are used for extremely important genes, like ribosomal RNA genes that are vital for organism function. The arrays serve to allow massive parallelized encoding of these genes, because many copies are required.
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A population of insects exists in which black coloration is dominant to white. If there are 64 black insects and 36 white insects in the population, what is the recessive allele frequency?
A population of insects exists in which black coloration is dominant to white. If there are 64 black insects and 36 white insects in the population, what is the recessive allele frequency?
We can use the white insect population to figure out our recessive allele frequency if we use the Hardy-Weinberg equations:
From this equation we know that 
is actually the frequency of our homozygous recessive genotype. We can determine the value of this genotypic frequency based on the information in the question. Any white insects must be homozygous recessive.
Solve for the recessive allele frequency.
We can use the white insect population to figure out our recessive allele frequency if we use the Hardy-Weinberg equations:
From this equation we know that
Solve for the recessive allele frequency.
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A population of lizards is shown to have 36 members that are homozygous dominant, 48 members that are heterozygous, and 16 members that are homozygous recessive for a particular trait. The population displays Hardy-Weinberg equilibrium. What are the allele frequencies present in this population?
A population of lizards is shown to have 36 members that are homozygous dominant, 48 members that are heterozygous, and 16 members that are homozygous recessive for a particular trait. The population displays Hardy-Weinberg equilibrium. What are the allele frequencies present in this population?
To solve this question, we must use the Hardy-Weinberg equations:
There are two ways to solve this problem. The easier way is to use the second Hardy-Weinberg equation. We are told that the population is in Hardy-Weinberg equilibrium, so the observed genotype frequencies equal the expected genotype frequencies. Each term in the second Hardy-Weinberg equation can be used in coordination with the given phenotypic frequencies.
The dominant allele frequency is 0.6 and the recessive allele frequency is 0.4.
The second method involves using our population and the total number of alleles. Since our population totals to 100, we have a total of 200 alleles (two alleles per member in the population. Next, to get the frequencies we simply have to divide the total number of a single allele by the total number of alleles in the population. For the dominant allele frequency it would look like this:
We can then get the recessive allele frequency from the first Hardy-Weinberg equation:
Both methods result in the same answer.
To solve this question, we must use the Hardy-Weinberg equations:
There are two ways to solve this problem. The easier way is to use the second Hardy-Weinberg equation. We are told that the population is in Hardy-Weinberg equilibrium, so the observed genotype frequencies equal the expected genotype frequencies. Each term in the second Hardy-Weinberg equation can be used in coordination with the given phenotypic frequencies.
The dominant allele frequency is 0.6 and the recessive allele frequency is 0.4.
The second method involves using our population and the total number of alleles. Since our population totals to 100, we have a total of 200 alleles (two alleles per member in the population. Next, to get the frequencies we simply have to divide the total number of a single allele by the total number of alleles in the population. For the dominant allele frequency it would look like this:
We can then get the recessive allele frequency from the first Hardy-Weinberg equation:
Both methods result in the same answer.
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A population of beetles exists in which black coloration is dominant to white. The allele frequencies of the population were originally o.4 for the dominant allele and 0.6 for the recessive allele. A predator was introduced that selectively ate the white beetles. The new population consists of 36 homozygous dominant black beetles, 48 heterozygous beetles, and 16 white beetles. What are the new allele frequencies?
A population of beetles exists in which black coloration is dominant to white. The allele frequencies of the population were originally o.4 for the dominant allele and 0.6 for the recessive allele. A predator was introduced that selectively ate the white beetles. The new population consists of 36 homozygous dominant black beetles, 48 heterozygous beetles, and 16 white beetles. What are the new allele frequencies?
The original allele frequencies are actually superfluous information that we will not need to use in our calculation. We are given the populations of each genotype, so we can use the Hardy-Weinberg equations to solve for the allele frequencies.
In the second equation, 
gives the frequency of the homozygous dominant phenotype and 
gives the frequency of the homozygous recessive phenotype. Using the population ratios from the question we can solve for these values to find the allele frequencies.
The problem could also be solved by summing the total number of alleles, and dividing the total of each individual allele by this number. Keep in mind that each individual carries two alleles.
The original allele frequencies are actually superfluous information that we will not need to use in our calculation. We are given the populations of each genotype, so we can use the Hardy-Weinberg equations to solve for the allele frequencies.
In the second equation,
The problem could also be solved by summing the total number of alleles, and dividing the total of each individual allele by this number. Keep in mind that each individual carries two alleles.
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Crossing foxes that are double heterozygotes for two genes regulating coat color yields 27 grey, 12 red and 9 black offspring. What mechanism explains the ratio of coat color observed in the offspring?
Crossing foxes that are double heterozygotes for two genes regulating coat color yields 27 grey, 12 red and 9 black offspring. What mechanism explains the ratio of coat color observed in the offspring?
If this were a Mendelian trait, we would expect a 9:3:3:1 ratio of offspring coat color. However, the results show a 9:4:3 ratio. Epistatic interaction between genes can be identified by one gene masking the phenotype of another gene. In this case, the double homozygote phenotype was masked by the red coat color phenotype (4 offspring, instead of seeing 3 red offspring). This suggests that the two coat color genes are epistatic.
If this were a Mendelian trait, we would expect a 9:3:3:1 ratio of offspring coat color. However, the results show a 9:4:3 ratio. Epistatic interaction between genes can be identified by one gene masking the phenotype of another gene. In this case, the double homozygote phenotype was masked by the red coat color phenotype (4 offspring, instead of seeing 3 red offspring). This suggests that the two coat color genes are epistatic.
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Which of the following choices are likely to change the allele frequencies of the indicated populations?
I. A geographic barrier isolating a small subset of a larger population
II. The introduction of a predator that only preys upon the homozygous dominant members of the population
III. A population that displays completely random mating
Which of the following choices are likely to change the allele frequencies of the indicated populations?
I. A geographic barrier isolating a small subset of a larger population
II. The introduction of a predator that only preys upon the homozygous dominant members of the population
III. A population that displays completely random mating
Allele frequencies are the measure of an allele in relation to the total number of alleles in the given population. Introducing a predator that only preys upon homozygous dominant members will cause the number of dominant alleles to drop significantly and will, therefore, change allele frequencies. This would be an example of the bottleneck effect. Isolating a small subset of a population is going to change allele frequencies because that small subset is not likely to accurately represent the original population. This is an example of the founder effect.
Random mating is actually a factor that helps maintain allele frequencies, and is a requirement for Hardy-Weinberg equilibrium.
Allele frequencies are the measure of an allele in relation to the total number of alleles in the given population. Introducing a predator that only preys upon homozygous dominant members will cause the number of dominant alleles to drop significantly and will, therefore, change allele frequencies. This would be an example of the bottleneck effect. Isolating a small subset of a population is going to change allele frequencies because that small subset is not likely to accurately represent the original population. This is an example of the founder effect.
Random mating is actually a factor that helps maintain allele frequencies, and is a requirement for Hardy-Weinberg equilibrium.
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Which of the following is not a condition for Hardy-Weinberg equilibrium?
Which of the following is not a condition for Hardy-Weinberg equilibrium?
Of the choices, the only one that is not a Hardy-Weinberg assumption is that natural selection is occurring on the population. In fact, the exact opposite is a Hardy-Weinberg assumption. If natural selection is occurring on a population, over a large period of time, it is likely to have an effect on allele frequencies within the population.
All other answers are requirements in order for Hardy-Weinberg equilibrium to be in effect: large population size, random mating, and negligible mutation frequencies.
Of the choices, the only one that is not a Hardy-Weinberg assumption is that natural selection is occurring on the population. In fact, the exact opposite is a Hardy-Weinberg assumption. If natural selection is occurring on a population, over a large period of time, it is likely to have an effect on allele frequencies within the population.
All other answers are requirements in order for Hardy-Weinberg equilibrium to be in effect: large population size, random mating, and negligible mutation frequencies.
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Which of the following conditions are not necessary for a population to be in Hardy-Weinberg equilibrium?
Which of the following conditions are not necessary for a population to be in Hardy-Weinberg equilibrium?
The Hardy-Weinberg equilibrium states that the frequency of alleles at a locus remains constant from generation to generation. In order for this to be the case, natural selection cannot affect the alleles under consideration. All other answer choices describe conditions that do need to be met for Hardy-Weinberg equilibrium to be displayed. Note that the conditions for Hardy-Weinberg equilibrium are not met in nature.
The Hardy-Weinberg equilibrium states that the frequency of alleles at a locus remains constant from generation to generation. In order for this to be the case, natural selection cannot affect the alleles under consideration. All other answer choices describe conditions that do need to be met for Hardy-Weinberg equilibrium to be displayed. Note that the conditions for Hardy-Weinberg equilibrium are not met in nature.
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An isolated population consists of 10 males and 10 females. Two individuals are carriers of the recessive blue eye allele. Assuming all Hardy-Weinberg conditions are met. What is the frequency of the blue eye phenotype in the population?
An isolated population consists of 10 males and 10 females. Two individuals are carriers of the recessive blue eye allele. Assuming all Hardy-Weinberg conditions are met. What is the frequency of the blue eye phenotype in the population?
Use the two Hardy-Weinberg equations:
Above, 
is the frequency of the dominant allele, and 
is the frequency of the recessive allele in the isolated population.
Since there are 20 people in total on the island, that means that there are 40 alleles for eye color. 2 of the 40 are for the blue allele:
We are looking for the blue eye phenotype, which can only result from two recessive alleles.
Use the two Hardy-Weinberg equations:
Above,
Since there are 20 people in total on the island, that means that there are 40 alleles for eye color. 2 of the 40 are for the blue allele:
We are looking for the blue eye phenotype, which can only result from two recessive alleles.
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Within his rat population, a scientist is trying to generate twice as many recessive homozygotes as heterozygotes. What allelic frequency would accomplish this?
Within his rat population, a scientist is trying to generate twice as many recessive homozygotes as heterozygotes. What allelic frequency would accomplish this?
Use the Hardy-Weinberg equations:
The equation he will need to set up is the following:
Solve for 
and substitute the first equation into the equation above.
Simplify.
Lastly, find 
.
Use the Hardy-Weinberg equations:
The equation he will need to set up is the following:
Solve for
Simplify.
Lastly, find
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A scientist has been working with a new species of plant. He has found that there are two separate genes, which segregate according to standard Mendelian genetics, that are capable of producing the same phenotype. A single dominant allele from either gene confers red coloration of the plant's flowers. Without any dominant alleles the flowers are white. If he crosses two plants heterozygous for both traits, what will be the resulting phenotypic ratios of the offspring?
A scientist has been working with a new species of plant. He has found that there are two separate genes, which segregate according to standard Mendelian genetics, that are capable of producing the same phenotype. A single dominant allele from either gene confers red coloration of the plant's flowers. Without any dominant alleles the flowers are white. If he crosses two plants heterozygous for both traits, what will be the resulting phenotypic ratios of the offspring?
This problem requires a standard dihybrid cross. The crossed genotypes are AaBb x AaBb. This results in a phenotypic ratio of 9 dominant for both traits, 3 dominant for a single trait, 3 dominant for the other trait, and 1 recessive for both traits. In this cross, it will result in: 9 AxBx, 3 Axbb, 3 aaBx, and 1 aabb.
Since we know that the genes are both capable of making the red coloration we actually need to add together all of the choices that contain at least a single dominant allele. Essentially, AxBx, Axbb, and aaBx all show the exact same phenotype. This leaves us with a 15:1 ratio of red to white flowers.
This problem requires a standard dihybrid cross. The crossed genotypes are AaBb x AaBb. This results in a phenotypic ratio of 9 dominant for both traits, 3 dominant for a single trait, 3 dominant for the other trait, and 1 recessive for both traits. In this cross, it will result in: 9 AxBx, 3 Axbb, 3 aaBx, and 1 aabb.
Since we know that the genes are both capable of making the red coloration we actually need to add together all of the choices that contain at least a single dominant allele. Essentially, AxBx, Axbb, and aaBx all show the exact same phenotype. This leaves us with a 15:1 ratio of red to white flowers.
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Assuming Hardy-Weinberg equilibrium conditions, what are the heterozygote (Bb) and homozygote recessive (bb) genotypes for a gene if the homozygote dominant (BB) genotype is 0.45?
Assuming Hardy-Weinberg equilibrium conditions, what are the heterozygote (Bb) and homozygote recessive (bb) genotypes for a gene if the homozygote dominant (BB) genotype is 0.45?
The correct answer is Bb = 0.44 and bb = 0.11.
Since we know BB = 0.45 and the equations for allele frequencies when Hardy-Weinberg equilibrium conditions are met:
and
We solve for B first:
Now we can solve for the homozygote recessive.
Lastly, solve for the heterozygote.
The correct answer is Bb = 0.44 and bb = 0.11.
Since we know BB = 0.45 and the equations for allele frequencies when Hardy-Weinberg equilibrium conditions are met:
and
We solve for B first:
Now we can solve for the homozygote recessive.
Lastly, solve for the heterozygote.
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Which of the following is not an assumption of the Hardy-Weinberg equilibrium?
Which of the following is not an assumption of the Hardy-Weinberg equilibrium?
Non-random mating is not an assumption of the Hardy-Weinberg equilibrium, in fact, in order to make predictions about the next generation, random mating must be assumed. Additionally, no new mutations, no gene flow, no genetic drift, and no natural selection must also occur. If any of these phenomenon are present in a population, we can not estimate allele frequencies in subsequent generations due to chance, rather selective pressures may favor one allele over another allele.
Non-random mating is not an assumption of the Hardy-Weinberg equilibrium, in fact, in order to make predictions about the next generation, random mating must be assumed. Additionally, no new mutations, no gene flow, no genetic drift, and no natural selection must also occur. If any of these phenomenon are present in a population, we can not estimate allele frequencies in subsequent generations due to chance, rather selective pressures may favor one allele over another allele.
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