Genetics - Chapter 18

A splice site mutation leading to loss of an exon can affect production of regions of the protein encoded in downstream exons even if they are spliced correctly. A) True B) False

A

A wild type allele: A) Is the allele that is the most common in the population. B) Is the allele with the highest level of functional protein. C) Is the most favorable allele in the population. D) All of the above. E) None of the above.

A

DNA repair systems typically work in three major steps: detection of the error, removal of the abnormality, and replacement of the removed DNA. A) True B) False

A

Increasing environmental levels of mutagen is likely to lead to increasing frequency of deleterious alleles. A) True B) False

A

Individuals with Cockayne syndrome are more likely to: A) Have an increased rate of somatic mutation. B) Have an increased rate of germ line mutation. C) Have a decreased rate of spontaneous mutation. D) Have a decreased rate of induced mutation.

A

In the Ames test: A) Mutagens cause lethal mutations, reducing the number of colonies. B) Mutagens cause mutations that disrupt the ability of the cell to produce histidine. C) Mutagens will cause an increase in the number of revertants. D) Only mutagens that cause transitions can be identified.

C

The main difference between the physiological adaptation theory and the random mutation theory is: A) The chemical nature of the mutagens. B) The effect of the mutation on the phenotype. C) The cause of the mutation. D) The heritability of the trait.

C

Which of the following would be an example of a germline mutation? A) Exposure to excessive UV radiation causes changes in the DNA of a skin cell, leading to basal cell carcinoma (skin cancer). B) In a very early human embryo, a mistake in mitosis causes loss of a Y chromosome in one daughter cell. The resulting child is a fertile male who is chromosomally partially male (XY) and partially female with Turner's syndrome (XO). C) A man with normal chromosomes has a hip X-ray without a protective shield. Ten months later, his wife gives birth to a child with a chromosomal deletion. D) An embryo missing one copy of the third chromosome is miscarried very early in pregnancy.

C

In which situation would you expect the mutation frequency to increase over time? A) The deleterious effect of the mutation is balanced with the mutation rate. B) A lethal allele is created at a high mutation rate. C) A neutral allele is created at low mutation rate. D) All of the above. E) None of the above.

C

Mitochondrial DNA polymerase does not have an error checking mechanism such as that of nuclear DNA polymerase. This would be expected to lead to a higher rate of which type of mutation in mitochondrial DNA? A) Spontaneous mutations. B) Induced mutations. C) Deletions. D) All of these. E) None of these.

A

The Luria-Delbrück fluctuation test was designed to differentiate between appearance of a trait due to random, spontaneous mutations vs. appearance of the trait due to adaptation to environmental conditions. A) True B) False

A

Which of the following forms of DNA repair does NOT require DNA polymerase? A) Direct DNA repair. B) Base excision repair. C) Nucleotide excision repair. D) Mismatch repair. E) Recombinational repair.

A

Differentiate between deleterious and lethal mutations.

A deleterious mutation reduces chances of survival/reproduction of an organism. A lethal allele is an extreme example of a deleterious allele that leads to the death of the organism.

Define a mutation.

A heritable change in the genetic material.

Describe a silent mutation.

A silent mutation is a change in the DNA sequence that does not alter the amino acid encoded. Like nonsense and missense mutations, silent mutations only occur in the protein coding region of a gene.

What might be a functional advantage to more efficient repair of actively transcribed genes?

Actively transcribed genes are presumably required for correct cellular function and thus mutations in them are more likely to have a deleterious effect. Also, these genes are loosely packaged, perhaps allowing more potential damage to bases. More efficient repair of these genes might offset an increased rate of damage.

Because they only affect a single amino acid, missense mutations do not have a significant effect on protein function. A) True B) False

B

Chromosomal rearrangements are unlikely to produce an obvious phenotype, since they do not remove any DNA. A) True B) False

B

Provided the number of base pairs is a multiple of three, insertion of additional DNA in the coding region of a protein is unlikely to have a dramatic effect on protein function. A) True B) False

B

The gene that is mutated in cases of cystic fibrosis encodes an ion transporter protein normally expressed in the respiratory and digestive tracts along with other locations. Individuals homozygous for the most common mutation in this gene (ΔF508) died at very early ages prior to the advent of advanced medical intervention. Despite this, the mutation exists at relatively high frequency in populations of European descent. One potential explanation is that heterozygotes for such mutations may be relatively immune to the lethal effects of diseases such as typhoid fever. Which statement below is most accurate? A) The ΔF508 cystic fibrosis mutation is a beneficial mutation. B) The ΔF508 cystic fibrosis mutation is a lethal mutation. C) The ΔF508 cystic fibrosis mutation is a conditional mutation. D) The ΔF508 cystic fibrosis mutation is a neutral mutation. E) The ΔF508 cystic fibrosis mutation is a suppressor mutation.

B

Which of the following point mutations would be most likely to affect protein function? A) TAA to TGA B) CAA to TAA C) AGG to AGA D) CTT to CTC E) All of these are likely to affect protein function.

B

Why is alkyltransferase only able to be used once? A) The protein is hydrolyzed in the process of repairing the DNa. B) The protein is chemically changed by the addition of a methyl group. C) The protein becomes attached to the DNA strand. D) All of these. E) None of these.

B

A bacterial cell experiences a mutation as a result of exposure to nitrogen mustard and then divides several times to produce a total of eight cells. How many of the resulting cells would you expect to contain the mutation? A) One B) Two C) Four D) Eight E) There is no way to tell.

C

A new chemical pesticide developed for agricultural use was subjected to the Ames test. The rate of mutation seen in samples treated with the pesticide and liver extract was approximately half that of the samples treated with the liver extract alone; in samples treated with only pesticide, the mutation rate was about the same as that of untreated samples. Which of the following statements could you make about this pesticide? A) The pesticide is modified by liver enzymes. B) The pesticide is unlikely to be a mutagen. C) The pesticide may be protective against spontaneous mutation. D) All of the above. E) E None of the above.

D

A woman with mild symptoms of myotonic muscular dystrophy has a daughter with a very severe form of the disease. Which of the following statements is most correct? A) The daughter probably has a mutation with the same number of repeats as her mother. B) The mother probably has a mutation with a larger number of repeats than the daughter. C) This must be an X-linked dominant condition. D) This is an example of anticipation.

D

Examples of environmental mutagens include: A) Alkylating agents, which chemically modify bases. B) Nucleotide base analogues. C) Ionizing radiation. D) All of these. E) None of these.

D

In Himalayan rabbits, the ears, feet, and muzzle are pigmented while the rest of the body is white. This is because they express an enzyme variant that is ineffective at body temperature but functions at the lower temperatures experienced by cells of the extremities. This is an example of: A) A wild type allele. B) A lethal mutation. C) A suppressor mutation. D) A conditional mutation.

D

Mutations: A) Are permanent changes in the DNA sequence or structure. B) Produce allelic variation. C) Are more likely to be harmful than beneficial. D) All of the above. E) None of the above.

D

The mutation which causes sickle cell anemia in humans: A) Is a base substitution. B) Is a deleterious mutation. C) Is a missense mutation. D) All of the above. E) None of the above.

D

A frameshift mutation could be caused by: A) A transition. B) A transversion. C) A deletion of 3 bp. D) All of these. E) None of these.

E

Based on the physiological adaptation theory, bacterial populations that had not been exposed to T1 infection: A) Should have a high level of resistance to T1 phage. B) Should be completely susceptible to infection by T1 phage. C) Should replicate more rapidly in the presence of T1 phage. D) All of the above. E) None of the above.

E

In a haploid organism, lethal alleles would be expected to: A) Have a high mutation frequency. B) Have a high mutation rate. C) Be caused only by induced mutations. D) All of the above. E) None of the above.

E

Which of these is NOT a mechanism by which a chromosome rearrangement could affect gene function? A) The breakpoint is in the middle of the coding region. B) The breakpoint is between the coding region and the regulatory elements. C) The new arrangement puts a gene near new regulatory elements. D) A gene is moved near a locus control region. E) None (all of these may be caused by rearrangements and affect gene function).

E

Explain how xeroderma pigmentosum can be caused by mutations in so many different genes.

In all cases of xeroderma pigmentosum, the nucleotide excision repair pathway is disrupted. Since many different proteins are required for this pathway to function correctly, mutations in any one protein of the pathway might be expected to lead to a similar phenotype.

Considering spontaneous mutations caused by depurination, deamination, and tautomeric shifts, explain why transitions are more common than transversions.

In depurination, only purines are affected but there is a 50:50 chance of insertion of a purine vs. a pyrimidine at the apurinic site after DNA replication. However, this would be expected to lead to equal numbers of transitions and transversions. Deamination only causes transitions, as it creates thymine or uracil from cytosine (indirectly, in the case of thymine). Tautomeric shifts also only cause transitions, as they still only allow base pairing between one purine and one pyrimidine but the specific pairs are changed. Therefore, two of these three causes of spontaneous mutations are only capable of creating transitions while the third should produce equal numbers of transitions and transversions.

What types of mutations might you expect to alter much or all of the primary structure of a protein?

Nonsense or frameshift.

Many eukaryotic genes have two stop codons located close to each other at the end of the gene. How might this be relevant for cells that carry a nonsense suppressor mutation?

Nonsense suppressors could allow translational readthrough of normal stop codons as well as the nonsense mutation. Presence of a second stop codon (especially if it is a different codon) would allow normal termination even if the nonsense suppressor allowed readthrough of the first stop codon.

For a gene with a mutation rate of 1 x 10-5 per generation, what additional information would you need to calculate the mutation frequency?

The mutation rate does not tell you anything about the current mutation frequency. To calculate mutation frequency, you need to know the population size (total number of alleles) and the number of mutant alleles.

How is mismatch repair able to determine the strand with the correct DNA sequence?

The parental strand is methylated and the newly made strand is not. The methylated strand then is used as a template to replace mismatches in the newly made strand.

As a result of the Chernobyl nuclear disaster, mutation rates in both humans and plants have been demonstrated to be greatly increased. What type of mutations would you expect to find in this population?

mall deletions or chromosomal rearrangements (result of crosslinking or chromosomal breaks) would be more common than base substitutions.

Differentiate between spontaneous and induced mutations.

spontaneous mutations result from abnormalities in normal biological processes such as DNA replication; induced mutations are caused by exposures to environmental mutagens such as UV radiation.

In Drosophila, the Torso protein is required for activation of a signaling pathway leading to formation of the head and tail of embryos. If Torso is missing ...

uppressor, intergenic suppressor, up promoter (since D-raf requires activation by Torso, this is unlikely in this scenario, however), missense. The mutation could NOT be a down promoter, intragenic suppressor, silent, nonsense, or neutral mutation. In the absence of additional information, you cannot determine if this mutation is deleterious, beneficial, or even lethal on its own.