Mutation and Variation - GRE

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Recombination between homologous chromosomes is one of the only methods for repairing double-stranded breaks in DNA without losing information. This method only works, however, if there is an extra copy of the same DNA in the cell (i.e. on a homologous chromosome). Recombination is not possible prior to the S phase of the cell cycle, during which DNA is replicated.

Non-homologous end joining results in the deletion of a few base pairs, which can be problematic if done in the coding region of a gene. Translesion synthesis actually has nothing to do with double-stranded breaks, and refers to a method of accurately synthesizing DNA over mutations (such as thymine dimers) by using specialized polymerases.

Recombination occurs between homologous chromosomes, not the sister chromatids, and this happens in prophase I of meiosis.

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.

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.

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.

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.

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.

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.

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.

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.