Genetics ch 18

Select which examples are induced mutations. A. Nitrous acid causes the deamination of cytosine to uracil. B. Errors in DNA replication cause the formation of point mutations. C. Ionizing radiation causes chromosomal fragmentation. D. Transposition causes the formation of insertions.

A. Nitrous acid causes the deamination of cytosine to uracil. C. Ionizing radiation causes chromosomal fragmentation.

What is a missense mutation? A. a mutation that results in a different amino acid in a protein B. a mutation that alters the reading frame of the gene C. a mutation whose effect is not yet known D. a mutation that changes a codon to a synonymous codon E. a mutation that changes a codon that specifies an amino acid to one that terminates translation

A. a mutation that results in a different amino acid in a protein

Which is not a characteristic of transposable elements? A. only found in plants B. able to insert at many different locations throughout a genome C. short flanking direct repeats present on both side of a transposon D. staggered breaks made in the target DNA during insertion E. can take place through a DNA intermediate in some cases

A. only found in plants

In recent years, advances in medical theraputic technologies have increased survival of children with cancer. However, some therapies such as high‑dose radiation can result in increased gametic (germline) mutations in treated individuals. These gametic mutations may alter the sex ratio of the offspring of childhood cancer survivors. Which scenarios correctly describe how a specific gametic mutation might alter the sex ratio in the offspring of a childhood cancer survivor? A. A decrease in male births can signal the introduction of a dominant lethal gametic mutation on the paternal autosome. B. A decrease in the number of female births can indicate that a dominant lethal gametic mutation has been introduced on the X chromosome transmitted by the father. C. A decrease in the number of male births can suggest that a recessive lethal gametic mutation has occurred on the X chromosome of the mother. D. A decline in the number of female births can provide evidence that a recessive lethal gametic mutation has been introduced into a paternal autosome.

B. A decrease in the number of female births can indicate that a dominant lethal gametic mutation has been introduced on the X chromosome transmitted by the father. C. A decrease in the number of male births can suggest that a recessive lethal gametic mutation has occurred on the X chromosome of the mother.

Which is an example of a transversion mutation? A. Thymine binds to a neighboring thymine base. B. Adenine is replaced by thymine. C. Guanine is replaced by adenine. D. Thymine is replaced by uracil. E. Cytosine is replaced by thymine.

B. Adenine is replaced by thymine.

DNA damage can occur as a result of exposure to chemicals or ultraviolet radiation. What happens during nucleotide excision repair of damaged DNA? A. Enzymes identify a mismatched base in a DNA strand, remove the incorrect base, and insert the correct base. B. Enzymes open the DNA strand, remove a segment of DNA from the strand that contains the damage, and resynthesize the correct DNA sequence. C. Enzymes delete an incorrect DNA sequence, pull the gap closed, and join the bases on either side of the gap together. D. Enzymes cut out the damaged gene, copy the same gene from the homologous chromosome, and insert the copy.

B. Enzymes open the DNA strand, remove a segment of DNA from the strand that contains the damage, and resynthesize the correct DNA sequence.

How does direct repair return DNA errors to their original sequences? A. It uses the other copy of the DNA molecule to replicate the original sequence. B. It removes functional groups or bonds from the altered nucleotide to restore the original structure. C. It uses an exonuclease to remove the incorrect sequence and replace it. D. It replaces altered nucleotides with the correct nucleotides. E. The base is first removed before the entire nucleotide is replaced.

B. It removes functional groups or bonds from the altered nucleotide to restore the original structure.

What generally causes thymine dimers to form in a strand of DNA, and why are thymine dimers a problem? A. Smoking often makes thymine dimers form, increasing the chance for mutations that lead to lung cancer. B. Thymine dimers, which can be produced by ultraviolet radiation, can lead to cancer‑causing mutations. C. Exposure to sunlight can create thymine dimers, which prevent the cell from initiating DNA replication. D. As cancer cells divide, thymine dimers may form and prevent nucleotide excision repair enzymes from working.

B. Thymine dimers, which can be produced by ultraviolet radiation, can lead to cancer‑causing mutations.

What is the Ames test? A. a test to determine how to reverse DNA mutations B. a test to screen for mutagenic chemicals C. a test to determine the phenotype of a mutation D. a test to determine the rate of mutation E. a test to find the cause of mutation

B. a test to screen for mutagenic chemicals

A cell with mutated DNA may not be able to produce proteins accurately. Which situations can lead to mutations in the DNA? A. mistakes in mRNA splicing B. chemicals in tobacco smoke C. uncorrected DNA replication errors D. ultraviolet radiation exposure E. excess pyruvate from glycolysis

B. chemicals in tobacco smoke C. uncorrected DNA replication errors D. ultraviolet radiation exposure

What disease occurs as a result of mutations in the genes for DNA repair systems? A. glaucoma B. xeroderma pigmentosum C. fragile X syndrome D. sickle cell anemia E. Huntington's disease

B. xeroderma pigmentosum

Which statement about mutations is incorrect? A. Gene mutations affect a single gene, whereas chromosome mutations affect the number or structure of chromosomes. B. Mutations are a source of all genetic variation. C. Germ-line and somatic mutations are both passed on to offspring. D. Somatic mutations are numerous, occurring at a rate one per every million cell division. E. Mutations can be used to examine biological processes.

C. Germ-line and somatic mutations are both passed on to offspring.

Which mutagens incorporate into DNA and frequently pair with the wrong base? A. deaminating chemicals B. alkylating agents C. base analogs D. oxidative radicals E. hydroxylamine

C. base analogs

Which type of DNA mutation results in a change in the reading frame of an mRNA? A. substitution of one codon for another B. deletion of a single codon C. insertion of a single nucleotide D. substitution of one nucleotide with another

C. insertion of a single nucleotide

How do mismatch‑repair enzymes in E. coli differentiate between the old and new strands of DNA? A. acetylation of the adenine in the GATC sequence of the old strand B. phosphorylation of the adenine in the GATC sequence of the new strand C. methylation of the adenine in the GATC sequence of the old strand D. methylation of adenine in the GATC sequence of the new strand E. phosphorylation of the adenine in the GATC sequence of the old strand

C. methylation of the adenine in the GATC sequence of the old strand

What is an environmental agent that significantly increases the rate of mutation above the spontaneous rate called? A. transposon B. Ames agent C. mutagen D. missense agent E. tautomer

C. mutagen

What changes does UV light produce in DNA molecules? A. purine dimers B. deamination C. pyrimidine dimers D. transversion mutations E. analog substitutions

C. pyrimidine dimers

In order to determine whether radiation associated with the atomic bombings of Hiroshima and Nagasaki produced recessive germ‑line mutations, scientists examined the sex ratio of the children of the survivors of the blasts. Why might an increase in germ‑line mutations be expected to alter the sex ratio? A. More females than males are expected to die because females do not have a Y chromosome that suppresses X‑linked recessive lethal mutations. B. More females than males are expected to die of sex‑linked recessive lethal mutations because females have two X chromosomes. C. More males than females are expected to die because of recessive lethal mutations on the Y chromosome. D. More males than females are expected to die of sex‑linked recessive lethal mutations because males have only one X chromosome.

D. More males than females are expected to die of sex‑linked recessive lethal mutations because males have only one X chromosome.

Which of the examples listed is not a DNA repair mechanism? A. direct repair B. base‑excision repair C. nucleotide‑excision repair D. insertion sequence repair E. mismatch repair

D. insertion sequence repair

How does transposition cause mutations? A. Transposable elements are carcinogens. B. Transposable elements can infect other cells and disrupt their genes. C. Transposition changes which amino acid is loaded onto a specific tRNA. D. Transposition "tags" the gene for degradation. E. Transposable elements can insert themselves into other genes and disrupt their function.

E. Transposable elements can insert themselves into other genes and disrupt their function.

What is a conditional mutation? A. a mutation that affects the genotype only under certain conditions B. a mutation that occurs only under certain conditions C. a mutation that makes it easier for organisms to contract diseases D. a mutation that affects the phenotype only when the organism is ill E. a mutation that affects the phenotype only under certain conditions

E. a mutation that affects the phenotype only under certain conditions

Barbara McClintock is known for her discovery of A. base analogs. B. tautomers. C. intercalating agents. D. the Ames test. E. transposons.

E. transposons.