All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #42 : Dna
Which of the following is NOT a type of mutation that can occur in DNA?
Silent
Countersense
Nonsense
Missense
Countersense
There are four principle types of mutation that can affect DNA. Most of these mutations result from point mutations affecting a single nucleotide residue, though nonsense mutations can be caused by insertions or deletions. Frame shift mutations are solely caused by insertions or deletions.
A silent mutation results from the degeneracy of the genetic code. In a silent mutation a single nucleotide is changed, but the overall translation product is unaffected. This can occur because multiple codons are capable of coding for the same amino acid.
A missense mutation results in the swapping of a single amino acid for another in the final translation product. If the amino acids are similar in character, missense mutations can still result in fully functional proteins. When the changed amino acid lacks characteristics of the original, it can result in protein misfolding and loss of function.
Nonsense mutations result in a premature stop codon, and early termination of the translation process. The final product is a shortened version of the protein, often lacking function.
Frame shift mutations cause a shift in the ribosomal reading frame. Every codon downstream of the mutation will be affected, and the protein will be completely altered. Frame shift mutations often result in premature stop codons.
Countersense is not a form of DNA mutation.
Example Question #1 : Mutation And Variation
Which of the following could cause a frameshift mutation?
Insertions or deletions
Mismatches
Insertions
Deletions
Insertions or deletions
Both insertions and deletions are capable of creating frameshift mutations. A frameshift mutation results in a shift in the reading frame of the gene, significantly altering translation. The cause of such a mutation is the insertion or deletion of any sequence of nucleotides within the gene that is not a multiple of three. The following examples detail different types of frameshift mutations.
Normal gene: ATT-CGT-AGG-TAC
Frameshift deletion examples: ATC-GTA-GGT-AC or ATT-CTA-C
Frameshift insertion examples: ATT-TCG-TAG-GTA-C or ACC-CGA-TAG-GTA-C
Mismatches would not cause a shift in the reading frame, like insertions or deletions.
Example Question #1 : Help With Mutation Types
A researcher has finally managed to design a plasmid that will allow him to begin expressing an important recombinant protein. After analyzing the sequencing data of the plasmid, however, he discovers that a mutation has occurred in the coding region of his protein. If he still wishes to express the wild type protein, does he need to construct a new plasmid?
No; one mutation should not affect the overall protein's function
It depends; a frameshift mutation would not affect the structure of the protein
Yes; any mutation is undesirable and will affect the protein's function
It depends; a silent mutation would not affect the structure of the protein
It depends; a silent mutation would not affect the structure of the protein
This question is somewhat vague because we are given no other information other than the fact that there is a "mutation". Mutations can take many different forms and, therefore, we would need to know more information about the specific type of mutation before we can say whether or not the plasmid still contains a functional gene for the wild type protein. In particular, a silent mutation would result in the insertion of the exact same amino acid despite having a different codon (this is due to the redundancy of the genetic code). If a silent mutation has altered the sequence of the plasmid, it will not alter the structure or function of the protein and the plasmid will still be effective.
A frameshift mutation, however, would have disastrous effects on the protein as the translational reading frame would be shifted and the protein would most likely be truncated and nonfunctional.
Example Question #2 : Mutation And Variation
Which of the following genotypes represents an individual with Turner syndrome?
YO
XXY
XXX
XYY
XO
XO
Individuals with Turners Syndrome have the XO genotype. They are phenotypically female but experience abnormalities. XXY is the genotype of an individual with Klinefelter syndrome. Individuals with the genotype XYY have what is known as XYY syndrome and are phenotypically normal, though they may be taller, and secrete excess testosterone. Triple-X syndrome is cause by an XXX genotype, and individuals are phenotypically normal. Lack of an X chromosome is lethal in humans.
Example Question #3 : Mutation And Variation
Which of the following terms best describes non-random association of alleles at different loci?
Linkage equilibrium
Crossing over
Independent assortment
None of the other answers
Linkage disequilibrium
Linkage disequilibrium
The correct answer is linkage disequilibrium. This phenomenon occurs when two alleles do not segregate independently even though they are at different loci. Rather, they are statistically associated with one another above non-random conditions. This is important for understanding evolution of organisms from a common ancestor as well as for identification of disease-associated mutations or single nucleotide polymorphisms.
Example Question #4 : Mutation And Variation
Which of the following does not contribute to linkage disequilibrium?
Natural selection
Rate of recombination
Rate of mutation
Genetic drift
Asexual reproduction
Asexual reproduction
The correct answer is asexual reproduction. Linkage disequilibrium is the non-random association of alleles at different loci. Under typical genetic assumptions, alleles segregate independently. However, some alleles have statistical significant association. There are many causes for this "linkage", including natural selection of linked genes that may confer increased fitness, recombination events bringing distant alleles in close proximity, genetic drift favoring a subset of alleles over another due to random sampling, and rate of mutation (either insertions or deletions) that result in statistical association between alleles.
Example Question #5 : Mutation And Variation
When mutations occur after the embryo has been fertilized and result in two or more genetically distinct populations of cells is best described as which of the following?
None of the other answers
Aneuploidy
Chimera
Mosaicism
Non-disjunction
Mosaicism
The correct answer is mosaicism. Mosaicism within an organism occurs when mutations, such as non-disjunction, occur in a subset of cells to give rise to genetically distinct cell populations. Chimeras also have genetically distinct cell populations, however, they occur from the fusion of two fertilized embryos. Aneuploidy occurs when an organism has an incorrect, but consistent number of chromosomes.
Example Question #6 : Mutation And Variation
If two alleles, that is both copies of a given gene, are required for proper function of that gene and its product, a mutation in just one of the copies will result in a mutant phenotype. This is called (a) __________.
hypomorphism
missense mutation
haplo-insufficiency
heterozygosity
homozygosity
haplo-insufficiency
Haplo-insufficent means that both copies of the gene must be fully functional to impart a wild-type phenotype. Mutating/inactivating one copy is enough to cause a mutant phenotype, which can result in a disordered state. Heterozygosity/homozygosity describe whether the alleles are the same or different, but do not necessarily describe the above case. A missense mutation is a type of mutation that changes the protein structure. A hypomorph is a type of mutation that results in reduced gene function, but does not necessarily describe the above case.
Example Question #7 : Mutation And Variation
Which of the following answers best describes a mutation where one allele is mutated in such a way that the resultant protein is structurally or functionally different, such that it interferes with the normal activity of the wild-type protein and disrupts that activity to form a partial or total mutant phenotype?
Nonsense mutation
Point mutation
Frameshift mutation
Missense mutation
Dominant-negative mutation
Dominant-negative mutation
While each of the mutations described above can lead to a dominant negative situation, the phrase dominant negative itself refers to the case where the mutant protein interacts with and interrupts the normal protein.
Example Question #8 : Mutation And Variation
Which of the following descriptions reflects a nonsense mutation?
An adenine is improperly added into a gene, resulting in a completely different amino acid sequence downstream to the mutation.
A transition mutation changes one nucleotide in a gene, but the final protein still has the same amino acid structure as it did prior to the mutation.
A mutation in a gene causes a valine to be replaced by a glutamic acid residue in the final protein product.
A uracil is replaced by an adenine in the primary transcript, resulting in a severely shortened final protein product.
A uracil is replaced by an adenine in the primary transcript, resulting in a severely shortened final protein product.
Answering this question requires an understanding of what a nonsense mutation will entail for a protein. Nonsense mutations occur when a mutation in a gene causes an amino acid codon to be converted into a stop codon. This premature stop codon will cause the translation of the primary transcript to be prematurely terminated, resulting in a smaller than normal protein product. The uracil to adenine mutation that made a smaller protein reflects this type of mutation.
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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
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