Genetic Abnormalities and Mutation - MCAT Biological and Biochemical Foundations of Living Systems
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Chromosomal aberrations, such as trisomy or monosomy, are often the result of nondisjunction during cell division. Nondisjunction is characterized by a malfunction during which stage of division?
Chromosomal aberrations, such as trisomy or monosomy, are often the result of nondisjunction during cell division. Nondisjunction is characterized by a malfunction during which stage of division?
This question is asking about the phase of Meiosis, during which disjunction (separation) of chromosomes normally occurs. While Metaphase can sometimes be a seductive answer, note that disjunction officially occurs during Anaphase.
This question is asking about the phase of Meiosis, during which disjunction (separation) of chromosomes normally occurs. While Metaphase can sometimes be a seductive answer, note that disjunction officially occurs during Anaphase.
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Which answer choice correctly shows a frameshift mutation?
Which answer choice correctly shows a frameshift mutation?
A framshift mutation is when an extra base is inserted into (or deleted from) a strand of DNA. When the DNA is transcribed, every codon downstream from the insertion is changed because the reading frame will be different. This will be the case for any mutations that affect a sequence of nucleotides that is not a multiple of three, for example a five-nucleotide deletion. Such mutations affect the three-nucleotide groupings for all codons following the mutation, and often result in a premature stop codon.
The correct answer is CGGTGAATAGGC 
CGGTGAATCAGGC. In the original sequence, the codons are CGG-TGA-ATA-GGC. In the second, they become CGG-TGA-ATC-AGG-C. The other answers show either insertions or deletions that do not shift the reading frame, or single nucleotide polymorphism (changing a single nucleotide to another).
Note that the reading frame does not change in the following 3-nucleotide insertion. Though there is an extra codon, the downstream sequence is not affected.
CGG-TGA-ATA-GGC 
CGG-TGA-AGA-CTA-GGC
A framshift mutation is when an extra base is inserted into (or deleted from) a strand of DNA. When the DNA is transcribed, every codon downstream from the insertion is changed because the reading frame will be different. This will be the case for any mutations that affect a sequence of nucleotides that is not a multiple of three, for example a five-nucleotide deletion. Such mutations affect the three-nucleotide groupings for all codons following the mutation, and often result in a premature stop codon.
The correct answer is CGGTGAATAGGC
Note that the reading frame does not change in the following 3-nucleotide insertion. Though there is an extra codon, the downstream sequence is not affected.
CGG-TGA-ATA-GGC
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Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
During meiosis, gametes result from the isolation of one chromosome from each of a human’s homologous 23 pairs. In Figure 2, der(14,21) is treated as a homologous pair to either 14 or 21. An egg, then, could be formed that had a normal chromosome 21 and the der(14,21) instead of the normal chromosome 14. If a sperm fertilizes this egg, and the sperm has a normal chromosome 14 and 21, what will result?
Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
During meiosis, gametes result from the isolation of one chromosome from each of a human’s homologous 23 pairs. In Figure 2, der(14,21) is treated as a homologous pair to either 14 or 21. An egg, then, could be formed that had a normal chromosome 21 and the der(14,21) instead of the normal chromosome 14. If a sperm fertilizes this egg, and the sperm has a normal chromosome 14 and 21, what will result?
Since the maternal oocyte would have two copies of chromosome 21, the normal 21 and the derivative chromosome, the normal addition of the sperm would lead to a zygote with a total of three copies of chromosome 21, or trisomy 21. Polyploidy is a tempting choice, but polyploid is a state characterized by extra copies of multiple chromosomes, as might be expected from more than one sperm fertilizing an egg.
Since the maternal oocyte would have two copies of chromosome 21, the normal 21 and the derivative chromosome, the normal addition of the sperm would lead to a zygote with a total of three copies of chromosome 21, or trisomy 21. Polyploidy is a tempting choice, but polyploid is a state characterized by extra copies of multiple chromosomes, as might be expected from more than one sperm fertilizing an egg.
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Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.
To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.
Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.
Which of the following genetic changes would not be detectable using FISH?
Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells.
To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.
Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below. In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.
Which of the following genetic changes would not be detectable using FISH?
FISH is useful for visualizing major changes in the genome, as described by the passage. Translocations and large copy number variants would likley be visible in color changes, while small single nucleotide polymorphisms (SNPs) would likely be less easily detected.
FISH is useful for visualizing major changes in the genome, as described by the passage. Translocations and large copy number variants would likley be visible in color changes, while small single nucleotide polymorphisms (SNPs) would likely be less easily detected.
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Cryptosporidium is a genus of gastrointestinal parasite that infects the intestinal epithelium of mammals. Cryptosporidium is water-borne, and is an apicomplexan parasite. This phylum also includes Plasmodium, Babesia, and Toxoplasma.
Apicomplexans are unique due to their apicoplast, an apical organelle that helps penetrate mammalian epithelium. In the case of cryptosporidium, there is an interaction between the surface proteins of mammalian epithelial tissue and those of the apical portion of the cryptosporidium infective stage, or oocyst. A scientist is conducting an experiment to test the hypothesis that the oocyst secretes a peptide compound that neutralizes intestinal defense cells. These defense cells are resident in the intestinal epithelium, and defend the tissue by phagocytizing the oocysts.
She sets up the following experiment:
As the neutralizing compound was believed to be secreted by the oocyst, the scientist collected oocysts onto growth media. The oocysts were grown among intestinal epithelial cells, and then the media was collected. The media was then added to another plate where Toxoplasma gondii was growing with intestinal epithelial cells. A second plate of Toxoplasma gondii was grown with the same type of intestinal epithelium, but no oocyst-sourced media was added.
You are conducting a study of an isolated tribe in New Guinea, and you find that there is widespread resistance to cryptosporidium infection. Upon examination, you find that the resistance is caused by a change in one nucleotide pair in a gene on chromosome 13. What kind of genetic change does this likely reflect?
Cryptosporidium is a genus of gastrointestinal parasite that infects the intestinal epithelium of mammals. Cryptosporidium is water-borne, and is an apicomplexan parasite. This phylum also includes Plasmodium, Babesia, and Toxoplasma.
Apicomplexans are unique due to their apicoplast, an apical organelle that helps penetrate mammalian epithelium. In the case of cryptosporidium, there is an interaction between the surface proteins of mammalian epithelial tissue and those of the apical portion of the cryptosporidium infective stage, or oocyst. A scientist is conducting an experiment to test the hypothesis that the oocyst secretes a peptide compound that neutralizes intestinal defense cells. These defense cells are resident in the intestinal epithelium, and defend the tissue by phagocytizing the oocysts.
She sets up the following experiment:
As the neutralizing compound was believed to be secreted by the oocyst, the scientist collected oocysts onto growth media. The oocysts were grown among intestinal epithelial cells, and then the media was collected. The media was then added to another plate where Toxoplasma gondii was growing with intestinal epithelial cells. A second plate of Toxoplasma gondii was grown with the same type of intestinal epithelium, but no oocyst-sourced media was added.
You are conducting a study of an isolated tribe in New Guinea, and you find that there is widespread resistance to cryptosporidium infection. Upon examination, you find that the resistance is caused by a change in one nucleotide pair in a gene on chromosome 13. What kind of genetic change does this likely reflect?
This would be an example of a single nucleotide polymorphism. A fairly common variant is some change at a single base pair in human DNA. It is possible that this base pair change results in a modified protein that functions just as well as the normal protein in most conditions.
Some of these changes may, simply by chance, be better at resisting disease. When exposed to stress, such as a disease epidemic, it is possible this variant of normal becomes the most widespread genotype. This is especially noticeable in an isolated population, like a tribe in New Guinea. Note that not all single nucleotide polymorphisms will have positive effects, and in some cases can cause disease instead of resistance.
This would be an example of a single nucleotide polymorphism. A fairly common variant is some change at a single base pair in human DNA. It is possible that this base pair change results in a modified protein that functions just as well as the normal protein in most conditions.
Some of these changes may, simply by chance, be better at resisting disease. When exposed to stress, such as a disease epidemic, it is possible this variant of normal becomes the most widespread genotype. This is especially noticeable in an isolated population, like a tribe in New Guinea. Note that not all single nucleotide polymorphisms will have positive effects, and in some cases can cause disease instead of resistance.
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An mRNA sequence is supposed to read UAUGGA, but a mutation replaces the second uracil base with guanine. What is the most specific term for this type of mutation?
An mRNA sequence is supposed to read UAUGGA, but a mutation replaces the second uracil base with guanine. What is the most specific term for this type of mutation?
This mutation replaced UAU (a coding codon) with UAG (a stop codon). The most descriptive term for this kind of replacement is a nonsense mutation.
Note that an easy way to remember the stop codons is UGA ("u" get away), UAA ("u" are away), and UAG ("u" are gone).
This mutation replaced UAU (a coding codon) with UAG (a stop codon). The most descriptive term for this kind of replacement is a nonsense mutation.
Note that an easy way to remember the stop codons is UGA ("u" get away), UAA ("u" are away), and UAG ("u" are gone).
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A mutation within a gene results in the premature addition of a stop codon during translation. This describes which type of mutation?
A mutation within a gene results in the premature addition of a stop codon during translation. This describes which type of mutation?
A nonsense mutation results in premature addition of a stop codon. A missense mutation is a point mutation that results in a different codon, which ultimately codes for a different amino acid in the polypetide sequence. A frameshift mutation results from and insertion or deletion of a nucleotide, resulting in a change in the reading frame. Frameshift mutations often indirectly result in nonsense mutations, but are not the best answer choice given.
A nonsense mutation results in premature addition of a stop codon. A missense mutation is a point mutation that results in a different codon, which ultimately codes for a different amino acid in the polypetide sequence. A frameshift mutation results from and insertion or deletion of a nucleotide, resulting in a change in the reading frame. Frameshift mutations often indirectly result in nonsense mutations, but are not the best answer choice given.
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Imagine there is a mutation in a gene where a nucleotide was replaced by another nucleotide. The mutation did not affect the primary structure of the protein for which the gene coded.
What type of mutation is this?
Imagine there is a mutation in a gene where a nucleotide was replaced by another nucleotide. The mutation did not affect the primary structure of the protein for which the gene coded.
What type of mutation is this?
Whenever a base pair is replaced by another base pair in the DNA double helix, it is referred to as a point mutation. If the amino acid is not changed by the mutation, we can refer to the mutation as a silent mutation, as the primary protein structure is not affected.
Point mutation: CATGA becomes CAGGA
Insertion mutations occur when additional bases are inserted into the DNA sequence.
Insertion mutation: CATGA becomes CATACTGA
Frameshift mutations can result from insertions or deletions when the number of nucleotides added/removed is not a multiple of three. Since codons are grouped by threes, any change that is not a multiple of three will alter the grouping of every codon downstream of the mutation, severly altering the primary protein structure.
Frameshift mutation: CATGA becomes CAATGA
A nonsense mutation results in a premature stop codon, and early translation termination. This can arise from a frameshift mutation, point mutation, insertion, or deletion.
Nonsense mutation: CATGA becomesCATTTAGA (When transcribed, this sequence becomes the mRNA UCUAAAUG, where UAA is a stop codon).
Whenever a base pair is replaced by another base pair in the DNA double helix, it is referred to as a point mutation. If the amino acid is not changed by the mutation, we can refer to the mutation as a silent mutation, as the primary protein structure is not affected.
Point mutation: CATGA becomes CAGGA
Insertion mutations occur when additional bases are inserted into the DNA sequence.
Insertion mutation: CATGA becomes CATACTGA
Frameshift mutations can result from insertions or deletions when the number of nucleotides added/removed is not a multiple of three. Since codons are grouped by threes, any change that is not a multiple of three will alter the grouping of every codon downstream of the mutation, severly altering the primary protein structure.
Frameshift mutation: CATGA becomes CAATGA
A nonsense mutation results in a premature stop codon, and early translation termination. This can arise from a frameshift mutation, point mutation, insertion, or deletion.
Nonsense mutation: CATGA becomesCATTTAGA (When transcribed, this sequence becomes the mRNA UCUAAAUG, where UAA is a stop codon).
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Consider the pedigree. Is the trait dominant or recessive?
Consider the pedigree. Is the trait dominant or recessive?
The trait is recessive because affected individuals do not occur in every generation. Additionally, dominant traits do not result in "carriers". Individuals are either affected or unaffected.
The trait is recessive because affected individuals do not occur in every generation. Additionally, dominant traits do not result in "carriers". Individuals are either affected or unaffected.
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Some inherited diseases of the liver, including Wilson's Disease, are primarily or entirely genetically determined. Wilson's Disease results when a defect in a copper transporter in the small intestine occurs, leading to copper level disregulation in both the hepatocytes and the systemic circulatory system. Mutations have primarily been found in the copper transporter that helps load copper onto a transport protein, apoceruloplasmin, which normally creates serum-soluble ceruloplasmin with the addition of copper. Given this defect, serum studies of an individual with Wilson's Disease would likely show what kind of change in serum ceruloplasmin compared with a normal individual?
Some inherited diseases of the liver, including Wilson's Disease, are primarily or entirely genetically determined. Wilson's Disease results when a defect in a copper transporter in the small intestine occurs, leading to copper level disregulation in both the hepatocytes and the systemic circulatory system. Mutations have primarily been found in the copper transporter that helps load copper onto a transport protein, apoceruloplasmin, which normally creates serum-soluble ceruloplasmin with the addition of copper. Given this defect, serum studies of an individual with Wilson's Disease would likely show what kind of change in serum ceruloplasmin compared with a normal individual?
The question informs us that the mutational defect in the gene involves the enzyme's ability to load copper onto apoceruloplasmin. Healthy individuals are able to load copper to apoceruloplasmin, creating serum-soluble ceruloplasmin. With this process disrupted in an individual with Wilson's Disease, we would expect that less ceruloplasmin would be produced because copper could not be transported. We would expect to see reduced serum levels of the complete protein, and high levels of copper building up in hepatocytes and circulatory serum.
The question informs us that the mutational defect in the gene involves the enzyme's ability to load copper onto apoceruloplasmin. Healthy individuals are able to load copper to apoceruloplasmin, creating serum-soluble ceruloplasmin. With this process disrupted in an individual with Wilson's Disease, we would expect that less ceruloplasmin would be produced because copper could not be transported. We would expect to see reduced serum levels of the complete protein, and high levels of copper building up in hepatocytes and circulatory serum.
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Which of the following represents a frameshift mutation to the given template strand?
5'-AGCCTTAGC-3'
Which of the following represents a frameshift mutation to the given template strand?
5'-AGCCTTAGC-3'
A frameshift mutation results in a change of the codon reading frame and results from the addition or deletion of a set of nucleotides that is not a multiple of three. If a mutation occurs that is a multiple of three, the reading frame is unchanged and a simple addition or deletion has occurred.
Template: 5'-AGC-CTT-AGC-3'
Frameshift mutant: 5'-AGC-GCT-TAG-C-3'
Point mutant: 5'-TGC-CTT-AGC-3'
Point mutant: 5'-AGC-CTT-AGG-3'
Deletion: 5'-CTT-AGC-3'
Insertion: 5'-TTT-AGC-CTT-AGC-3'
Note that all except the frameshift mutation contain sets of three nucleotides to create triplets. The frameshift leaves a singular, un-grouped cytosine.
A frameshift mutation results in a change of the codon reading frame and results from the addition or deletion of a set of nucleotides that is not a multiple of three. If a mutation occurs that is a multiple of three, the reading frame is unchanged and a simple addition or deletion has occurred.
Template: 5'-AGC-CTT-AGC-3'
Frameshift mutant: 5'-AGC-GCT-TAG-C-3'
Point mutant: 5'-TGC-CTT-AGC-3'
Point mutant: 5'-AGC-CTT-AGG-3'
Deletion: 5'-CTT-AGC-3'
Insertion: 5'-TTT-AGC-CTT-AGC-3'
Note that all except the frameshift mutation contain sets of three nucleotides to create triplets. The frameshift leaves a singular, un-grouped cytosine.
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The concept of genomic imprinting is important in human genetics. In genomic imprinting, a certain region of DNA is only expressed by one of the two chromosomes that make up a typical homologous pair. In healthy individuals, genomic imprinting results in the silencing of genes in a certain section of the maternal chromosome 15. The DNA in this part of the chromosome is "turned off" by the addition of methyl groups to the DNA molecule. Healthy people will thus only have expression of this section of chromosome 15 from paternally-derived DNA.
The two classic human diseases that illustrate defects in genomic imprinting are Prader-Willi and Angelman Syndromes. In Prader-Willi Syndrome, the section of paternal chromosome 15 that is usually expressed is disrupted, such as by a chromosomal deletion. In Angelman Syndrome, maternal genes in this section are deleted, while paternal genes are silenced. Prader-Willi Syndrome is thus closely linked to paternal inheritance, while Angelman Syndrome is linked to maternal inheritance.
Figure 1 shows the chromosome 15 homologous pair for a child with Prader-Willi Syndrome. The parental chromosomes are also shown. The genes on the mother’s chromosomes are silenced normally, as represented by the black boxes. At once, there is also a chromosomal deletion on one of the paternal chromosomes. The result is that the child does not have any genes expressed that are normally found on that region of this chromosome.
In addition to the chromosomal deletion on chromosome 15 in the passage, the father is found to have another gene with a mutation, which adds a stop codon prematurely in the base pair sequence. This mutation is best described as a
.
The concept of genomic imprinting is important in human genetics. In genomic imprinting, a certain region of DNA is only expressed by one of the two chromosomes that make up a typical homologous pair. In healthy individuals, genomic imprinting results in the silencing of genes in a certain section of the maternal chromosome 15. The DNA in this part of the chromosome is "turned off" by the addition of methyl groups to the DNA molecule. Healthy people will thus only have expression of this section of chromosome 15 from paternally-derived DNA.
The two classic human diseases that illustrate defects in genomic imprinting are Prader-Willi and Angelman Syndromes. In Prader-Willi Syndrome, the section of paternal chromosome 15 that is usually expressed is disrupted, such as by a chromosomal deletion. In Angelman Syndrome, maternal genes in this section are deleted, while paternal genes are silenced. Prader-Willi Syndrome is thus closely linked to paternal inheritance, while Angelman Syndrome is linked to maternal inheritance.
Figure 1 shows the chromosome 15 homologous pair for a child with Prader-Willi Syndrome. The parental chromosomes are also shown. The genes on the mother’s chromosomes are silenced normally, as represented by the black boxes. At once, there is also a chromosomal deletion on one of the paternal chromosomes. The result is that the child does not have any genes expressed that are normally found on that region of this chromosome.
In addition to the chromosomal deletion on chromosome 15 in the passage, the father is found to have another gene with a mutation, which adds a stop codon prematurely in the base pair sequence. This mutation is best described as a .
The best answer is a nonsense mutation, which is defined as a point mutation that gives rise to an early stop codon, thus truncating any protein products prematurely. These are typically devastating mutations for protein function.
The best answer is a nonsense mutation, which is defined as a point mutation that gives rise to an early stop codon, thus truncating any protein products prematurely. These are typically devastating mutations for protein function.
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Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
| | 0 min | 30 min | 60 min | 90 min | 120 min | |
| ------------ | ---------- | ---------- | ---------- | ----------- | --- |
| Group A | 80 | 150 | 120 | 90 | 80 |
| Group B | 90 | 220 | 180 | 160 | 140 |
| Group C | 100 | 260 | 190 | 150 | 135 |
| Group D | 75 | 145 | 110 | 90 | 75 |
Based on the data, what role does Dia play in insulin regulation?
Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
| | 0 min | 30 min | 60 min | 90 min | 120 min | | | ------------ | ---------- | ---------- | ---------- | ----------- | --- | | Group A | 80 | 150 | 120 | 90 | 80 | | Group B | 90 | 220 | 180 | 160 | 140 | | Group C | 100 | 260 | 190 | 150 | 135 | | Group D | 75 | 145 | 110 | 90 | 75 |
Based on the data, what role does Dia play in insulin regulation?
The beta cell-specific Dia mutation in group C causes results similar to the global Dia mutation in group B. From this, we can conclude that Dia is functioning within the beta cells. Essentially, deleting Dia from the beta-cells is equivalent to deleting it from the entire body. Additionally, loss of Dia in skeletal muscle in group D seems to have no phenotypic effect, indicating that Dia is not necessary in skeletal muscle.
Pancreatic beta cells are responsible for insulin production, while skeletal muscle plays a significant role in insulin sensitivity. Since loss of Dia in beta cells leads to high blood glucose, we can conclude that the role of Dia is in the promoting the production of insulin, and that the gene plays no role in insulin sensitivity.
The beta cell-specific Dia mutation in group C causes results similar to the global Dia mutation in group B. From this, we can conclude that Dia is functioning within the beta cells. Essentially, deleting Dia from the beta-cells is equivalent to deleting it from the entire body. Additionally, loss of Dia in skeletal muscle in group D seems to have no phenotypic effect, indicating that Dia is not necessary in skeletal muscle.
Pancreatic beta cells are responsible for insulin production, while skeletal muscle plays a significant role in insulin sensitivity. Since loss of Dia in beta cells leads to high blood glucose, we can conclude that the role of Dia is in the promoting the production of insulin, and that the gene plays no role in insulin sensitivity.
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Which of the following will least likely affect the length of a protein product?
Which of the following will least likely affect the length of a protein product?
A missense mutation is the substitution of one nucleotide for another in the DNA sequence, resulting in a different resulting amino acid. Essentially, one amino acid is replaced with another. This type of mutation will not alter the overall protein length.
A nonsense mutation results in a pre-mature stop codon, causing early termination of the protein product and a shorter protein. Frameshift mutations commonly cause pre-mature stop codons to arise, and at the very least will result in a highly altered protein product that is likely of a different length from the unaltered protein. Single-base addition and deletions will cause frameshift mutations.
Healthy RNA: 3'-AGG-UCG-UUA-GUC-5'
Missense: 3'-AAG-UCG-UUA-GUC-5'
Nonsense: 3'-AGG-UAG-5' (UAG stop codon)
Frameshift: 3'-AAG-GUC-GUU-AGU-C-5' (single-base addition)
Framshift: 3'-AGU-CGU-UAG-5' (single-base deletion, UAG stop codon)
A missense mutation is the substitution of one nucleotide for another in the DNA sequence, resulting in a different resulting amino acid. Essentially, one amino acid is replaced with another. This type of mutation will not alter the overall protein length.
A nonsense mutation results in a pre-mature stop codon, causing early termination of the protein product and a shorter protein. Frameshift mutations commonly cause pre-mature stop codons to arise, and at the very least will result in a highly altered protein product that is likely of a different length from the unaltered protein. Single-base addition and deletions will cause frameshift mutations.
Healthy RNA: 3'-AGG-UCG-UUA-GUC-5'
Missense: 3'-AAG-UCG-UUA-GUC-5'
Nonsense: 3'-AGG-UAG-5' (UAG stop codon)
Frameshift: 3'-AAG-GUC-GUU-AGU-C-5' (single-base addition)
Framshift: 3'-AGU-CGU-UAG-5' (single-base deletion, UAG stop codon)
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Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).
An individual containing three sex chromosomes (XXY) is called a polysomic individual. What is the reason for polysomy?
Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).
An individual containing three sex chromosomes (XXY) is called a polysomic individual. What is the reason for polysomy?
The question states that the individual with three sex chromosomes has a condition called polysomy. Recall that a normal individual will only carry two copies of a chromosome.
This abnormality occurs when meiosis isn’t carried out properly. A daughter cell from meiosis can contain an extra chromosome if sister chromatids don’t separate properly during anaphase II (a process called nondisjunction). This extra chromosome can be carried over to the offspring, giving rise to a polysomic individual.
Fertilization of two sperm cells with two eggs gives rise to fraternal twins (non-identical twins) and splitting of a single fertilized egg into two or more eggs gives rise to monozygotic twins (identical twins); therefore, you can eliminate these two answer choices. After meiosis, females always possess multiple polar bodies. During meiosis in females, most of the cellular content is transferred to a single daughter cell: the egg. The remaining daughter cells contain the remnants and are called polar bodies. These polar bodies don’t participate in development and fertilization.
The question states that the individual with three sex chromosomes has a condition called polysomy. Recall that a normal individual will only carry two copies of a chromosome.
This abnormality occurs when meiosis isn’t carried out properly. A daughter cell from meiosis can contain an extra chromosome if sister chromatids don’t separate properly during anaphase II (a process called nondisjunction). This extra chromosome can be carried over to the offspring, giving rise to a polysomic individual.
Fertilization of two sperm cells with two eggs gives rise to fraternal twins (non-identical twins) and splitting of a single fertilized egg into two or more eggs gives rise to monozygotic twins (identical twins); therefore, you can eliminate these two answer choices. After meiosis, females always possess multiple polar bodies. During meiosis in females, most of the cellular content is transferred to a single daughter cell: the egg. The remaining daughter cells contain the remnants and are called polar bodies. These polar bodies don’t participate in development and fertilization.
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Which of the following mutations might lead to the formation of a recessive allele?
I. Silent
II. Frameshift
III. Nonsense
IV. Missense
Which of the following mutations might lead to the formation of a recessive allele?
I. Silent
II. Frameshift
III. Nonsense
IV. Missense
Recessive alleles are often created by mutated versions of functional genes that encode broken/nonfunctional proteins. The question is thus asking us which of the mutations is likely to result in a nonfunctional or abnormal protein.
Silent mutations are types of mutations that result in the insertion of the same amino acid due to the degeneracy of the genetic code and, therefore, will not cause any noticeable change in the protein. Essentially, even organisms with the mutation will still show the dominant allele.
Frameshift mutations change the reading frame used for translation and oftentimes result in premature stop codons. Nonsense mutations are mutations that specifically result in premature stop codons and generally result in nonfunctional proteins. Missense mutations lead to the insertion of a different amino acid at the normal site. This can lead to serious problems for the functionality of the protein, particularly if the mutation is present in the active site or another area that is highly conserved throughout evolution.
Recessive alleles are often created by mutated versions of functional genes that encode broken/nonfunctional proteins. The question is thus asking us which of the mutations is likely to result in a nonfunctional or abnormal protein.
Silent mutations are types of mutations that result in the insertion of the same amino acid due to the degeneracy of the genetic code and, therefore, will not cause any noticeable change in the protein. Essentially, even organisms with the mutation will still show the dominant allele.
Frameshift mutations change the reading frame used for translation and oftentimes result in premature stop codons. Nonsense mutations are mutations that specifically result in premature stop codons and generally result in nonfunctional proteins. Missense mutations lead to the insertion of a different amino acid at the normal site. This can lead to serious problems for the functionality of the protein, particularly if the mutation is present in the active site or another area that is highly conserved throughout evolution.
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Which of the following mutations will not change the amino acid sequence of the polypeptide created during translation?
Which of the following mutations will not change the amino acid sequence of the polypeptide created during translation?
A silent mutation is a mutation that results in the inclusion of the same amino acid in the polypeptide product, despite a change in the DNA template sequence. Silent mutations generally involve the third nucleotide in the codon sequence, since this unit is often interchangeable due to the degeneracy of the coding sequence.
A missense mutation results in a different amino acid inclusion based on codon alteration. A nonsense mutation is the insertion of a new stop codon as a result of mutation, resulting in a truncated polypeptide and severely hindering functionality. An insertion or frameshift mutation can change the reading frame of the mRNA template, drastically changing the identity and primary sequence of the polypeptide product; these are the most dangerous type of mutation, as the product may be harmful as well as nonfunctional.
A silent mutation is a mutation that results in the inclusion of the same amino acid in the polypeptide product, despite a change in the DNA template sequence. Silent mutations generally involve the third nucleotide in the codon sequence, since this unit is often interchangeable due to the degeneracy of the coding sequence.
A missense mutation results in a different amino acid inclusion based on codon alteration. A nonsense mutation is the insertion of a new stop codon as a result of mutation, resulting in a truncated polypeptide and severely hindering functionality. An insertion or frameshift mutation can change the reading frame of the mRNA template, drastically changing the identity and primary sequence of the polypeptide product; these are the most dangerous type of mutation, as the product may be harmful as well as nonfunctional.
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Which of the following DNA changes is least likely to alter the translated amino acid sequence created by the sequence below?
5'-CGATGAACG-3'
Which of the following DNA changes is least likely to alter the translated amino acid sequence created by the sequence below?
5'-CGATGAACG-3'
First, you want to narrow down the answers to those with the fewest changes (1 base change). Next, you needed to select the single base change on the third base of the codon. A silent mutation (a DNA mutation that doesn't result in an amino acid change) is most likely to occur when the third base of a codon is changed.
Original sequence: 5'-CGA TGA ACG-3'
Unaltered mRNA transcript: 3'-GCU ACU UGC-5'
Note that the mRNA sequence is antiparallel, changing the orientation of the codons. mRNA is read in the 5'-to-3' direction by the ribosome, meaning that the third base in the codon will be to the left of the 3-base sequence. The given RNA sequence will be read as CGU UCA UCG.
Correct answer: 5'-CGA CGA ACG-3'
Altered mRNA transcript: 3'-GCU GCU UGC-5'
The sequence will be read as CGU UCG UCG.
The correct answer involves a mutation in the third nitrogenous base of the second codon. Both UCA (original) and UCG (altered) code for serine.
First, you want to narrow down the answers to those with the fewest changes (1 base change). Next, you needed to select the single base change on the third base of the codon. A silent mutation (a DNA mutation that doesn't result in an amino acid change) is most likely to occur when the third base of a codon is changed.
Original sequence: 5'-CGA TGA ACG-3'
Unaltered mRNA transcript: 3'-GCU ACU UGC-5'
Note that the mRNA sequence is antiparallel, changing the orientation of the codons. mRNA is read in the 5'-to-3' direction by the ribosome, meaning that the third base in the codon will be to the left of the 3-base sequence. The given RNA sequence will be read as CGU UCA UCG.
Correct answer: 5'-CGA CGA ACG-3'
Altered mRNA transcript: 3'-GCU GCU UGC-5'
The sequence will be read as CGU UCG UCG.
The correct answer involves a mutation in the third nitrogenous base of the second codon. Both UCA (original) and UCG (altered) code for serine.
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Chromosomal aberrations, such as trisomy or monosomy, are often the result of nondisjunction during cell division. Nondisjunction is characterized by a malfunction during which stage of division?
Chromosomal aberrations, such as trisomy or monosomy, are often the result of nondisjunction during cell division. Nondisjunction is characterized by a malfunction during which stage of division?
This question is asking about the phase of Meiosis, during which disjunction (separation) of chromosomes normally occurs. While Metaphase can sometimes be a seductive answer, note that disjunction officially occurs during Anaphase.
This question is asking about the phase of Meiosis, during which disjunction (separation) of chromosomes normally occurs. While Metaphase can sometimes be a seductive answer, note that disjunction officially occurs during Anaphase.
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Which answer choice correctly shows a frameshift mutation?
Which answer choice correctly shows a frameshift mutation?
A framshift mutation is when an extra base is inserted into (or deleted from) a strand of DNA. When the DNA is transcribed, every codon downstream from the insertion is changed because the reading frame will be different. This will be the case for any mutations that affect a sequence of nucleotides that is not a multiple of three, for example a five-nucleotide deletion. Such mutations affect the three-nucleotide groupings for all codons following the mutation, and often result in a premature stop codon.
The correct answer is CGGTGAATAGGC CGGTGAATCAGGC. In the original sequence, the codons are CGG-TGA-ATA-GGC. In the second, they become CGG-TGA-ATC-AGG-C. The other answers show either insertions or deletions that do not shift the reading frame, or single nucleotide polymorphism (changing a single nucleotide to another).
Note that the reading frame does not change in the following 3-nucleotide insertion. Though there is an extra codon, the downstream sequence is not affected.
CGG-TGA-ATA-GGC CGG-TGA-AGA-CTA-GGC
A framshift mutation is when an extra base is inserted into (or deleted from) a strand of DNA. When the DNA is transcribed, every codon downstream from the insertion is changed because the reading frame will be different. This will be the case for any mutations that affect a sequence of nucleotides that is not a multiple of three, for example a five-nucleotide deletion. Such mutations affect the three-nucleotide groupings for all codons following the mutation, and often result in a premature stop codon.
The correct answer is CGGTGAATAGGC
Note that the reading frame does not change in the following 3-nucleotide insertion. Though there is an extra codon, the downstream sequence is not affected.
CGG-TGA-ATA-GGC
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