Question 1

Adenine methylase is an enzyme used during mismatch repair MMR).It helps determine which strand needs to be repaired by discriminating between template and new DNA strand.If this enzyme is mutated,how would MMR be affected?

Accepted Answer

If adenine methylase is mutated, both strands would be unmethylated, and both would appear as new DNA strands. MMR relies on identifying the template strand, which is the methylated strand. If both strands are unmethylated, MMR would not be able to determine which strand is the template and which is the new strand, hindering the repair process.

Question 2

In bacteria and eukaryotes,a mutation is when__________ .

Accepted Answer

A mutation is a change in the nucleotide sequence of a DNA molecule. This change can alter the amino acid sequence in a protein molecule if it occurs within a coding region of DNA. Mutations can occur spontaneously or be induced by exposure to environmental factors such as radiation or chemicals.

Question 3

Tautomeric shifts__________ .

Accepted Answer

Tautomeric shifts can cause mispairings of nucleotides during DNA replication, resulting in changes to the genetic code and potentially causing missense mutations. They can lead to base substitutions but not to frame shifts, insertion or deletion mutations. Tautomeric shifts do not allow purines to bind to purines or pyrimidines to bind to pyrimidines as they still follow the complementary base pairing rules.

Question 4

Thymine dimers form when __________.

Accepted Answer

Thymine dimers form when two thymines on the same strand and adjacent to each other bind together, usually due to exposure to UV radiation.

Question 5

At what stage is a mutation predicted to have the effect?

Accepted Answer

Mutations that affect development and growth are expected to occur early, during embryonic development, which is when the basic body plan is established. Mutations that occur later may still have an effect, but are less likely to have as significant an impact on overall growth and development. Therefore, the best choice is D, during early embryonic development.

Question 6

A geneticist is studying a particular Drosophila mutant that produces a phenotype of "no wing" due to a mutation in a gene called wingless.She takes the mutant wingless and mutagenizes it.She hypothesizes that any fly that emerges with wings will be due to the original mutated gene reverting back to the wild- type allele. From this study,she identifies a fly that now has wings.When she sequences the wingless gene,she discovers that the original mutation is still there,and there are no other mutations in the wingless gene.However,a second gene at a separate locus is mutated.The second mutation is best classified as an__________.

Accepted Answer

The presence of a second mutation at a separate locus that restores the wild-type phenotype (in this case, the ability to form wings) is an example of an intergenic suppressor mutation.

Question 7

Which f the following mutagens is matched correctly with its action?

Accepted Answer

Ethidium bromide is correctly matched with its action as an intercalating agent. Intercalating agents insert themselves between the base pairs in the DNA double helix, distorting the DNA structure and interfering with DNA replication and transcription.

Question 8

A class of mutations that results in multiple contiguous amino acid changes in proteins is likely to be which of the following?

Accepted Answer

Frameshift mutations would cause a shift in the reading frame of the DNA sequence, resulting in a completely different amino acid sequence downstream of the mutation. This would lead to multiple contiguous amino acid changes in the protein. The other choices do not necessarily result in multiple contiguous amino acid changes.

Question 9

Ultraviolet light causes pyrimidine dimers to form in DNA.Some individuals are genetically incapable of repairing some dimers at "normal" rates.Such individuals are likely to suffer from__________ .

Accepted Answer

Xeroderma pigmentosum is a genetic disorder characterized by a deficiency in the ability to repair pyrimidine dimers caused by ultraviolet light. This leads to an increased risk of skin cancer and other skin abnormalities. Choice B (muscular dystrophy) is a genetic disorder that affects muscle function, Choice C (Huntington disease) is a genetic disorder that affects brain function, Choice D (phenylketonuria) is a genetic disorder that affects amino acid metabolism, and Choice E (SCID) is a genetic disorder that affects the immune system. These disorders are not related to the formation of pyrimidine dimers in DNA.

Question 10

Transposons,or jumping genes,are DNA elements that move within the genome.In which organismic groups are transposons found?

Accepted Answer

Transposons, or "jumping genes," are found across all organismic groups, including mammals, bacteria (both ancient and modern), and eukaryotes, reflecting their fundamental role in genetic evolution and diversity.

Question 11

Which of the following mutations would be classified as a transversion?

Accepted Answer

A transversion is a point mutation that involves the substitution of a purine for a pyrimidine or vice versa. In this case, CGA (coding for arginine, a purine) to CGT (coding for arginine, a pyrimidine) is a substitution of a purine for a pyrimidine and therefore a transversion. The other options are all substitutions of one purine for another (Option A and D) or one pyrimidine for another (Option C) and are therefore classified as transitions. Option B is a substitution of a pyrimidine for a purine but, specifically, a substitution of guanine for adenine which would also be classified as a transversion, but it is not the best option since Option E is a more precise answer.

Question 12

Which of the following two mutagens that would be classified as base analogs?

Accepted Answer

Base analogs are chemicals that are similar in structure to the bases found in DNA, and they can substitute for these bases during DNA synthesis. 5-Bromouracil and 2-amino purine are both examples of base analogs, as they can substitute for thymine and adenine, respectively, in DNA replication. The other choices (hydroxyurea, peroxidase, ultraviolet light, cosmic radiation, ethylmethane sulfonate, ethylmethylketone peroxide, acridine orange, and proflavine) are not base analogs, as they do not mimic the chemical structure of DNA bases.

Question 13

Which repair mechanism is most likely affected if the enzyme DNA glycosylase is not functioning properly?

Accepted Answer

DNA glycosylase is an enzyme involved in base excision repair, specifically in the removal of damaged or abnormal bases. If it is not functioning properly, this repair mechanism would be affected.

Question 14

Mutations that arise in nature,from no particular artificial agent,are called __________ .

Accepted Answer

Spontaneous mutations are those that occur naturally and randomly, without being induced by any particular external agent. They can arise from errors in DNA replication, spontaneous chemical reactions, or other internal biological processes. In contrast, induced mutations are caused by known external agents such as radiation or certain chemicals, while nutritional mutations and chromosomal losses are specific types of genetic changes that can occur due to certain factors or conditions. Cosmic mutations are not a recognized term in the field of genetics.

Question 15

A mutation that changes an amino acid- coding codon to a stop codon is classified as what kind of codon?

Accepted Answer

A mutation that changes an amino acid-coding codon to a stop codon is called a nonsense mutation. This type of mutation creates a premature termination codon, which leads to the premature termination of the polypeptide chain and often results in a nonfunctional protein.

Question 16

Germ cell mutations__________ .

Accepted Answer

Germ cell mutations occur in the cells that give rise to gametes (sperm and eggs) and can therefore be passed on to the next generation. These mutations are not usually found in every cell of the next generation, but rather only in the gametes that were affected. This is why some genetic disorders or diseases may be present in multiple generations of a family, as they are being passed down through the germ line. Germ cell mutations can occur in both males and females and are not specific to one sex. Testicular cancer may be caused by mutations in germ cells, but this is not the only cause of the disease. Somatic cell mutations, on the other hand, affect the genetic makeup of non-reproductive cells and can impact the function of the individual in the current generation.

Question 17

Which of the following diseases are caused by an expansion of trinucleotide repeats?

Accepted Answer

Fragile X syndrome is caused by an expansion of trinucleotide repeats in the FMR1 gene. Achondroplasia is caused by a point mutation, cystic fibrosis by a deletion, beta-thalassemia by a variety of mutations, and Marfan's syndrome by a mutation in the FBN1 gene.

Question 18

From the Luria- Delbruck fluctuation test,when would mutations arise in yeast cells to allow for survival in the presence of toxic levels of hydrogen peroxide?

Accepted Answer

The Luria-Delbrück fluctuation test demonstrates that mutations occur randomly and not in response to environmental challenges. Therefore, mutations that allow yeast cells to survive in toxic levels of hydrogen peroxide would have occurred randomly prior to exposure to the hydrogen peroxide.

Question 19

One would predict that bacteria that lack the enzyme photolyase would be more sensitive to what kind of mutagen?

Accepted Answer

Photolyase is an enzyme that repairs DNA damage caused by UV light. Therefore, bacteria lacking photolyase would be more sensitive to UV light, which is a type of mutagen that causes thymine dimers in DNA. Choice A, B, C and E are not directly related to the absence of photolyase.

Question 20

During the Ames test,his- bacteria are exposed to a chemical.If the bacteria remains his+,then what can we say about the chemical?

Accepted Answer

If the bacteria remains his+ in the Ames test, it means that the chemical is likely a mutagen, which can cause changes in the DNA and potentially lead to cancer. Therefore, the chemical is not safe to consume.

Quiz 15: Gene Mutation,dna Repair,and Transposition

Adenine methylase is an enzyme used during mismatch repair MMR) .It helps determine which strand needs to be repaired by discriminating between template and new DNA strand.If this enzyme is mutated,how would MMR be affected?