Mutation MCQ Quiz - Objective Question with Answer for Mutation - Download Free PDF

The correct answer is Temperature sensitive, dominant

Explanation:

• The mutation described causes a reduction in eye size in Drosophila at 29°C but has no effect at 18°C. This indicates that the mutation is temperature sensitive because its phenotypic effects are dependent on the environmental temperature.
• The phenotype is observable even when the animal has only one copy of the mutation, which characterizes the mutation as dominant. Dominant mutations are observable even in heterozygous individuals.
• Thus, the mutation is best described as temperature sensitive, dominant.

The correct answer is Biallelic heterozygous mutations

Concept:

1. Monoallelic mutations: Mutations occurring in only one of the two alleles of a gene in a diploid organism.
2. Biallelic mutations: Mutations occurring in both alleles of a gene. This can further be classified into:
   • Biallelic homozygous mutations: Both alleles have the same type of mutation (e.g., both have the same addition or deletion).
   • Biallelic heterozygous mutations: Each allele has a different mutation (e.g., one allele has an addition and the other has a deletion).
3. Chimeric mutations: Refers to a mixture of cells with different genetic compositions, often resulting from techniques like CRISPR-Cas9, but this term usually describes the overall plant rather than specific mutations in alleles.

Explanation:

• Allele 1 has a frameshift mutation due to the deletion of three nucleotides.
• Allele 2 has a missense mutation caused by a single nucleotide substitution.
• These mutations are clearly different and occur on separate alleles, indicating that both alleles are mutated but not in the same way.
• Since different mutations are observed in both alleles, this scenario represents biallelic heterozygous mutations.
• Neither allele is identical in its mutation, ruling out biallelic homozygous mutations.
• Both alleles are affected, ruling out monoallelic mutations.

Therefore, the correct answer is Biallelic heterozygous mutations

The correct answer is Frameshift

Explanation:

• A frameshift mutation occurs when there is an insertion or deletion (indel) of nucleotides that are not in multiples of three, altering the reading frame of the genetic code.
• This leads to a complete shift in how the codons are read during translation, potentially altering all downstream amino acids or introducing premature stop codons.
• Comparing the sequencing gels of the wild type (Figure A) and the mutant (Figure B), there is a clear shift in the alignment of bands after a specific point. This is indicative of an insertion or deletion, which causes a change in the reading frame.
• This disruption continues throughout the sequence, consistent with the nature of a frameshift mutation.

Other Options:

• Nonsense Mutation: A nonsense mutation introduces a premature stop codon, truncating the protein. This would result in a shorter sequence on the gel. The gel shows a continued sequence with a shift in the pattern, rather than a premature truncation.
• Missense Mutation: A missense mutation results in a single base substitution, leading to one amino acid being replaced by another. The gel shows multiple shifted bands, indicating a frameshift caused by insertion or deletion rather than a single substitution.
• Transversion: A transversion mutation is a point mutation where a purine (A or G) is replaced by a pyrimidine (C or T), or vice versa. A transversion affects only a single base pair, which would appear as a single difference between the wild type and mutant sequences. The gel demonstrates a shift in multiple bands, 

The correct answer is A, B and C

Concept:

• Translocation refers to exchange of chromosomal segments between two non-homologous chromosomes. It can be of two types: reciprocal and non-reciprocal.
  • Non-reciprocal translocation involves the transfer of segment in one direction from one chromosome to another. 
  • Reciprocal translocation involves exchange of the segments of chromosomes between non-homologous chromosomes, this results in the generation of two translocated chromosomes simultaneously. 

Explanation:

Types of Segregation: The three modes of segregation (adjacent 1, adjacent 2, and alternate) occur in reciprocal translocation heterozygotes.

• Alternate Segregation: Opposite chromosomes (diagonally) in the cross segregate into the same gamete. This leads to viable gametes, as these gametes either contain both normal chromosomes or both translocated chromosomes.
• Adjacent 1 Segregation: Adjacent chromosomes segregate vertically, resulting in one normal and one translocated chromosome per gamete. This often leads to non-viable gametes due to duplications and deletions of genetic material.
• Adjacent 2 Segregation: Adjacent chromosomes segregate horizontally, resulting in one normal and one translocated chromosome per gamete. This also leads to non-viable gametes because of genetic imbalances.

​

Dicentric (two centromeres) and acentric (no centromere) chromosomes are not a consequence of reciprocal translocations during alternate segregation. Instead, they occur during structural rearrangements like inversion. Thus, statement D is incorrect.

The correct answer is biallelic heterozygous mutations.

Concept:

Definitions of Mutation Types:

1. Monoallelic mutations: Mutations occurring in only one of the two alleles of a gene in a diploid organism.
2. Biallelic mutations: Mutations occurring in both alleles of a gene. This can further be classified into:
   • Biallelic homozygous mutations: Both alleles have the same type of mutation (e.g., both have the same addition or deletion).
   • Biallelic heterozygous mutations: Each allele has a different mutation (e.g., one allele has an addition and the other has a deletion).
3. Chimeric mutations: Refers to a mixture of cells with different genetic compositions, often resulting from techniques like CRISPR-Cas9, but this term usually describes the overall plant rather than specific mutations in alleles.

Explanation:

• Allele 1 has an addition of a nucleotide.
• Allele 2 has a deletion of a nucleotide.

Since there are mutations in both alleles, and the mutations are different (one is an addition and the other is a deletion), this scenario represents a case of biallelic heterozygous mutations.

Conclusion: The correct classification of the observed mutations is biallelic heterozygous mutations. This is because both alleles of the target gene have been mutated, but they have different types of mutations (addition vs. deletion).

The correct answer is C and D.

Concept:

• Synonymous Mutations: These mutations occur in a DNA sequence but do not change the amino acid sequence of the protein that is produced. This occurs because of the redundancy in the genetic code, where multiple codons can encode the same amino acid. Since the resulting protein remains unchanged, synonymous mutations are often considered neutral, meaning they neither benefit nor harm the organism.
• Non-Synonymous Mutations: These mutations result in a change in the amino acid sequence of the protein, which can alter the protein's structure and function. Non-synonymous mutations are further divided into two types:
  • Missense Mutations: These mutations change a single amino acid in the protein sequence.
  • Nonsense Mutations: These mutations introduce a premature stop codon, leading to a truncated and often non-functional protein.

Explanation:

Purifying selection, also known as negative selection, is a type of natural selection that acts to eliminate deleterious mutations from a population. Under purifying selection, mutations that are harmful to the organism are selected against, while neutral or beneficial mutations persist.
A. Most non-synonymous mutations are selected against.

• Non-synonymous mutations result in a change in the amino acid sequence of proteins. Many such changes can impair protein function, thus, under purifying selection, most non-synonymous mutations are indeed selected against to maintain protein functionality.
• Under purifying selection, these harmful mutations are typically removed from the population
• True under purifying selection: Yes, this statement is correct for purifying selection.

B. Synonymous mutations can accumulate.

• Synonymous mutations do not change the amino acid sequence of proteins due to the redundancy of the genetic code. Since they do not affect the protein function, they are generally neutral and can accumulate over time because they are not subject to strong selective pressure.
• True under purifying selection: Yes, this statement is correct for purifying selection.

C. The ratio of non-synonymous to synonymous substitutions is high.

• Under purifying selection, non-synonymous mutations (which could alter protein function and often reduce organism fitness) are selected against much more strongly than synonymous mutations. Thus, the ratio of non-synonymous to synonymous substitutions is expected to be low.
• True under purifying selection: No, this statement does not fit the expectations of purifying selection.

D. Non-synonymous sites accumulate mutations at higher rates.

• Given that non-synonymous mutations are often deleterious, purifying selection acts to remove them, leading to a lower rate of accumulation compared to synonymous mutations.
• True under purifying selection: No, this statement is incorrect for purifying selection.

Conclusion
Under purifying selection, harmful mutations, particularly those that change the amino acid sequence of proteins, are removed from the population. Therefore, The correct option that is NOT true about sequence evolution under purifying selection is:

• C. The ratio of non-synonymous to synonymous substitutions is high.
• D. Non-synonymous sites accumulate mutations at higher rates.

The correct answer is Option 2 i.e. B and C

Concept:

• Mutation is defined as the abrupt change in the genetic material of the organism.
• Spontaneous mutations are always occurring in nature these are called background mutations. 
• The induced mutation is the mutation that is artificially introduced in the organisms by exposing the organism to some abnormal environment such as radiation, chemical, mutagens, etc. 

Mutagen Types - 

1. Physical - It includes ionizing as well as non-ionising radiation such as X-rays, gamma rays, alpha rays, etc.
2. Biological - It can be virus or bacteria that can induce mutation in organisms. for example, Pyroli is implicated in stomach cancer and papillomavirus is implicated in cervical cancer. 
3. Chemical -
   • Base analogues - these compounds are analogous to the bases present in DNA, for example, 2-aminopurine, 5-bromouracil, etc.
   • Base-modifying agents - they cause changes in the bases of the DNA, for example, Nitrous acid, hydroxylamine, etc.
   • Intercalating agents - These chemicals intersect between the DNA bases there by disrupting the helical nature of the DNA. For example, proflavin, acridine orange, etc.

Explanation:

Statement A: CORRECT

• If the DNA sequence is changed from AGC to ATC then the codon will change from UCG to UAG in the mRNA.
• UCG codes for serine while UAG is the stop codon. In the mRNA, instead of serine amino acid, mRNA will be terminated. 
• So, it leads to premature termination of the mRNA. 
• Hence, this is a correct statement.

Statement B: INCORRECT

• A reverse mutation is a mutation that restores the original phenotype by causing a mutation in the origin site. 
• A suppressor mutation also restores the original phenotype but the site of the mutation is different from the original mutation. 
• Hence, this is an incorrect statement. 

Statement C: INCORRECT

• Mutation rates are not the same in all organisms it changes from one organism to another.
• Hence, this is an incorrect statement, 

Statement D: CORRECT

• Slippage can lead to mutation in the DNA, it occurs during DNA replication. 
• It involved denaturation followed by displacement of the DNA strands that result in mispairing of the complementary bases. 
• Hence, single-stranded loop formation leads to slippage because during replication DNA strands are separated which causes displacement of small sections of DNA. 
• Hence, this is a correct statement. 

Statement E: CORRECT

• Hydroxylamine is a very potent mutagen as it causes hydroxylation of cytosine base in the DNA leading to the formation of  hydroxylaminocytosine.
• So, hydroxylamine adds OH group to the cytosine.
• Hence, this is a correct statement. 

Hence, the correct answer is Option 2. 

Concept:

• strains with gene A mutations can be represented as having the genotype aa, whereas strains with gene B mutations can be represented as having the genotype bb.
• Each of these mutant strains can be more accurately described as aaBB and AAbb as there are only two genes present, A and B.
• The offspring produced by crossing these two strains will all be AaBb. They will have a pigmented, purple flower, a wild-type phenotype, and both a wild-type, functional A gene, and B gene.
• This is a good illustration of complementarity. Each strain fills the gaps that the others have when combined (AaBb).
• Since the mutations affect various genes, they are known as non-allelic mutations.

Explanation:

• It indicates that the two mutations are nonallelic, meaning they lie on two distinct genes if two mutants when crossed result in offspring with a wild-type phenotype.
• In the progeny where one wildtype copy of the gene is given by each parent, complementation occurs and a wildtype phenotype is seen.
• Generally, mutant alleles are recessive to their wild type or normal alleles.
• These mutations are non-allelic, meaning they lie on different loci.

Key PointsBase analog

• Certain bases that are not normally present in DNA but bear a strong structural resemblance to normal nitrogenous bases can be incorporated from the appropriate triphosphate precursor during DNA synthesis.
• These compounds are called base analogs.
• For example, 5-bromouracil (5-BU) is an analog of thymine that has bromine at the C-5 position in place of CH, group found in thymine.
• 5-BU has the same base-pairing properties as thymine, and nucleotides containing the base can be added to the daughter polynucleotide at positions opposite as in the template.
• The common keto form of 5-BU pairs with adenine.
• 5-BU confrequently change to the enol form.
• The mutagenic effect arises because the equilibrium between the two tautomers of 5-BU is shifted more towards the rare enol form than is the case with thymine.
• It means that during the next round of replication, there is a relatively high chance of the polymerase encountering enol-5BU, which (like enol-thymine) pairs with G rather than A.
• This results in a point mutation.
• 2-Aminopurine (2-AP) acts in the similar way.
• It is an analog of adenine with an amino-tautomeric form pairs with thymine and an imino tautomeric form pairs with cytosine.
• But the imino form of 2-AP being more common than imino form of adenine and hence inducing T-to-C transitions during DNA replication (AT→ GC transition).

Explanation:

• It is an analog of adenine with an amino-tautomeric form pairs with thymine and an imino tautomeric form pairs with cytosine.
• But the imino form of 2-AP being more common than imino form of adenine and hence inducing T-to-C transitions during DNA replication (AT→ GC transition).

Hence the correct answer is option 4

Concept:

• The base analogue of adenine called 2-aminopurine (2-AP) mispairs with cytosine and results in base-pair substitutions of the transition type.
• The adenine base analog 2-aminopurine (2AP) is a potent base substitution mutagen in prokaryotes because of increased ability to form a mutagenic base pair with an incoming dCTP.

​Explanation:

• Research studies confirmed that 2-AP induces both A:T leads to G:C and G:C leads to A:T transitions, with the former occurring more frequently than the latter.
• These compounds result in DNA lesions when they are integrated into DNA.
• These lesions will result in mutations if the mismatch correction system does not rectify the mismatches.
• Normally, these lesions do not activate the SOS functions and act as miscoding lesions.

​​hence the correct answer is option 2

The correct answer is Option 3

Explanation:

• A silent mutation is a type of mutation where a change in the DNA sequence does not affect the amino acid sequence of the protein produced from that gene. This type of mutation usually occurs in the third base of a codon, where changes due to the degeneracy of the genetic code do not alter the amino acid being coded.
• In the case of a silent mutation, the genetic sequence (genotype) has changed due to the mutation; however, because the mutation does not alter the protein (due to the redundancy in the genetic code), the observable traits or characteristics (phenotype) of the organism remain unchanged compared to the wild type.

The correct answer is Acridine orange

Explanation:

• DNA intercalators are molecules that can insert themselves between the base pairs of the DNA double helix. This can disrupt the structure of the DNA and interfere with processes such as replication and transcription.
• Intercalation is a mode of action for some chemotherapeutic agents used in cancer treatment because it can inhibit the proliferation of cancer cells.
• Acridine orange: Acridine orange is a well-known DNA intercalator. It inserts itself between the base pairs of the DNA double helix, causing structural disruptions. This property makes it useful for various biochemical and medical applications, including fluorescence microscopy and cancer treatment.
• 5-Bromouracil: 5-Bromouracil is a base analog that gets incorporated into DNA in place of thymine. It does not intercalate between DNA strands but instead causes mutations by pairing with guanine instead of adenine.
• Ethyl methane sulfonate: Ethyl methane sulfonate (EMS) is an alkylating agent that induces mutations by adding alkyl groups to DNA bases, leading to mispairing and errors during DNA replication. It does not intercalate into DNA.
• UV: Ultraviolet (UV) radiation causes thymine dimers to form in DNA, leading to mutations. UV radiation does not intercalate into DNA but instead causes direct damage to the DNA structure.

The correct answer is: relative locations of genes on a chromosome

Explanation:

• A genetic linkage map is a map of the relative positions of genetic loci (genes or other hereditary markers) on a chromosome based on the frequencies of recombination between them.
• These maps are constructed by determining the recombination frequency between pairs of genes during crossover events in meiosis. The lower the recombination frequency, the closer the genes are presumed to be on a chromosome.
• Genetic linkage maps do not provide accurate physical distances; instead, they provide estimates of the distances based on genetic recombination data.

Additional Information:

• Genetic linkage maps are useful for identifying the location of genes associated with particular traits or diseases.
• They are different from physical maps of chromosomes, which show the actual physical distances between loci measured in base pairs.
• The creation of genetic linkage maps is an essential tool in genetics and genomics, aiding in the study of genetic inheritance and the function of genes.
• The recombination frequency \((( \theta ))\) is given by the formula:\( [ \theta = \frac{\text{Number of recombinant offspring}}{\text{Total number of offspring}} ]\)
• The recombination frequency is expressed as a percentage and it can be converted into map units, also known as centimorgans (cM). One map unit or centimorgan corresponds to a 1% recombination frequency.

The correct answer is mutagenic carcinogens

Explanation:

• The Ames test specifically detects mutagens that are suspected of being carcinogenic by observing whether the tested chemicals cause mutations in the DNA of a bacterium (commonly Salmonella typhimurium).
• If the chemical causes mutations, it suggests that it might also be capable of causing mutations in human DNA, thereby increasing the risk of cancer. This makes the test a valuable tool in chemical safety testing and epidemiological studies related to cancer risk.

Methodology

• Strain Selection: The bacteria used in this test are specially selected strains of Salmonella typhimurium that carry mutations in genes involved in histidine synthesis. These mutations prevent the bacteria from growing on a medium lacking histidine unless a second mutation reverses this inability.
• Exposure to Chemicals: The test substance is added to a culture of the mutated bacteria along with a small amount of histidine. The mixture is plated on a medium that lacks histidine.
• Incubation: During incubation, if the test substance causes mutations that reverse the histidine synthesis block (back-mutation), the bacteria will be able to grow and form colonies.
• Results Interpretation: The number of colonies reflects the mutagenic potential of the substance. A higher number of colonies indicates a higher mutagenic potential.