Genetics Chapter 14

Which of the following statements regarding Nucleotide Excision Repair (NER) and Base Excision Repair (BER) is true?

Both NER and BER involve the removal of one or more damaged bases by a nuclease. Correct. This statement is true. In both NER and BER a nuclease will target damaged or distorted regions of DNA.

Which nucleotide will base‑pair with the enol form of 5‑bromouracil?

Guanine The enol form of 5‑bromouracil forms a base pair with guanine.

Which of the following statements most accurately describes the transposable genetic elements found in corn?

The earlier in kernel development a reversion event occurs, the larger the spot of tissue exhibiting the reversion phenotype. Correct. The earlier in development the reversion occurs, the greater the number of divisions the reverted cell type undergoes before kernel development is complete.

What are the consequences of having pyrimidine dimers in DNA?

These dimers distort the DNA structure and result in errors during DNA replication.

This sequence represents a single mutation. Mutation #1: 5' - | GGC | GCG | GTA | TTA | GCG | - 3'

This mutant DNA sequence is the result of a transition (transition or transversion?) mutation. The effect of this base substitution on the amino acid sequence results in a missense mutation.

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?

a frameshift deletion at the beginning of the gene A frameshift mutation at the beginning of a gene would affect every codon after the point where the mutation occurred. During protein synthesis, incorrect amino acids would be inserted from the point where the frameshift mutation occurred on; the resulting protein would most probably be nonfunctional. For this reason, a frameshift mutation at the beginning of a gene is generally the most severe type of mutation.

Which of the following events could result in a frameshift mutation?

base deletion A base deletion would shorten the DNA sequence and change the reading frame of the mRNA.

Autonomous elements can transpose by themselves even though they cannot produce transposase.

false Correct. Transposase is required for transposition of both autonomous and non-autonomous transposons, but autonomous elements produce their own transposase.

The purpose of the Ames Test is to _______.

test the mutagenic effects of chemicals Correct. The Ames test detects whether a given chemical can cause a reversion mutation in his- bacteria.

This sequence represents a single mutation. Mutation #2: 5' - | GGC | GTG | GTA | TAA | GCG | - 3'

This mutant DNA sequence is the result of a transversion (transition or transversion?) mutation. The effect of this base substitution on the amino acid sequence results in a nonsense mutation.

This sequence represents a single mutation. Mutation #3: 5' - | GGC | GTG | GTC | TTA | GCG | - 3'

This mutant DNA sequence is the result of a transversion (transition or transversion?) mutation. The effect of this base substitution on the amino acid sequence results in a silent mutation.

When a base substitution mutation occurs, one nucleotide in a replicating DNA sequence is substituted for another, which results in the production of a mutant strand of DNA. The result of the mutation depends on how the substituted nucleotide base alters the string of amino acids coded by the mutant DNA. The three types of base substitution mutations are nonsense mutations, missense mutations, and silent mutations. Each type is defined by how it affects protein synthesis.

a) silent mutation b)nonsense mutation c)missense mutation d) frameshift mutation Point mutations in DNA sequences can profoundly affect protein synthesis, or they can have no effect at all. Point mutations can be beneficial to an organism but are more commonly neutral or harmful.

If a segment of DNA were replicated without any errors, the replicated strand would have the following sequence of nucleotides: 5' - ACTACGTGA - 3' Sort the following replicated DNA sequences by the type of point mutation each contains (frameshift, base substitution, or neither), as compared to the correct sequence shown above.

frameshift mutations: 5'-ACTTACGTGA-3' , 5'-ACTCGTGA-3' base substitution mutations: 5'-ACTACGTGT-3', 5'- ACTAAGTGA-3'

In the Ames Test, the appearance of his+ revertants in the presence of a non-mutagenic control compound indicates that _______.

some of the reversion mutations are not caused by the mutagen being tested Correct. His+ revertants on the control plate are the result of spontaneous mutation.

The purple spots on colorless background of corn kernels observed by Barbara McClintock were the result of _______.

transposition of the Ds elements out of the color gene Correct. Upon loss of Ds from the color gene "C" sequence, wild-type (purple) phenotype results in cells in which the loss has occurred.

Thymine dimers can be repaired by Photoreactivation Repair or Nucleotide Excision Repair.

true Both Photoreactivation Repair and Nucleotide Excision Repair will target UV-induced pyrimidine dimers in DNA.

Many chemicals are more mutagenic after being processed in the liver.

true Correct. Many potential mutagens are poorly mutagenic until passing through the liver.

Tautomers of nucleotide bases are isomers that differ from each other in the location of one hydrogen atom in the molecule.

true Nucleotide tautomers differ only in the bonding location of one hydrogen atom.