In March 2011 an earthquake measuring approximately 9.0 on the Richter scale struck Fukushima, Japan. Several nuclear reactors at the Fukushima Daichii Nuclear Power Plant were damaged, and nuclear core meltdown occurred. A massive release of radiation accompanied damage to the plant, and 5 years later the incidence of thyroid cancer in children exposed to the radiation was determined to be well over 100 times more frequent than expected without radiation exposure. DNA damage and mutations resulting from radiation exposure are suspected of causing this increased cancer rate. What gene discussed in this chapter might be responsible for pausing the cell cycle of dividing cells long enough for radiation-induced damage to be repaired in cells?

In March 2011 an earthquake measuring approximately 9.0 on the Richter scale struck Fukushima, Japan. Several nuclear reactors at the Fukushima Daichii Nuclear Power Plant were damaged, and nuclear core meltdown occurred. A massive release of radiation accompanied damage to the plant, and 5 years later the incidence of thyroid cancer in children exposed to the radiation was determined to be well over 100 times more frequent than expected without radiation exposure. DNA damage and mutations resulting from radiation exposure are suspected of causing this increased cancer rate. Do you think it is possible that significant increases in the incidence of other types of cancer will occur in the future among people who were exposed to the Fukushima radiation? Why?

For the retinal cancer retinoblastoma, the inheritance of one mutated copy of RB1 from one of the parents is often referred to as a mutation that produces a 'dominant predisposition to cancer.' This means that the first mutation does not produce cancer but makes it very likely that cancer will develop. Define the 'two-hit hypothesis' for retinoblastoma.

Identify two general ways chemical mutagens can alter DNA. Give examples of these two mechanisms.

Nitrous acid and 5-bromodeoxyuracil (BrdU) alter DNA by different mechanisms. What type of mutation does each compound produce?

What is the difference between a transition mutation and a transversion mutation?

What are the differences between a synonymous mutation, a missense mutation, and a nonsense mutation?

UV irradiation causes damage to bacterial DNA. What kind of damage is frequently caused and how does photolyase repair the damage?

Ultraviolet (UV) radiation is mutagenic.

What kind of DNA lesion does UV energy cause?

Ultraviolet (UV) radiation is mutagenic.

How do UV-induced DNA lesions lead to mutation?

Ultraviolet (UV) radiation is mutagenic.

Identify and describe two DNA repair mechanisms that remove UV-induced DNA lesions.

Researchers interested in studying mutation and mutation repair often induce mutations with various agents. What kinds of gene mutations are induced by

Chemical mutagens? Give two examples.

Researchers interested in studying mutation and mutation repair often induce mutations with various agents. What kinds of gene mutations are induced by

Radiation energy? Give two examples.

The effect of base-pair substitution mutations on protein function varies widely from no detectable effect to the complete loss of protein function (null allele). Why do the functional consequences of base-pair substitution vary so widely?

Describe the purpose of the Ames test. How are his⁻ bacteria used in the Ames test? What mutational event is identified using his⁻ bacteria?

In numerous population studies of spontaneous mutation, two observations are made consistently: (1) Most mutations are recessive, and (2) forward mutation is more frequent than reversion. What do you think are the likely explanations for these two observations?

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNAᵀʳᵖ from

   3′−ACC−5′ to 3′−ACU−5′

Do you consider the first mutation to be a forward mutation or a reversion? Why?

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNAᵀʳᵖ from

   3′−ACC−5′ to 3′−ACU−5′

Do you consider the second mutation to be a forward mutation or a reversion? Why?

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the ade-1 gene. In this mutation, a base-pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base-pair substitution mutation changes the anticodon sequence of a tRNAᵀʳᵖ from

   3′−ACC−5′ to 3′−ACU−5′

Assuming there are no other mutations in the genome, will this double-mutant yeast strain be able to grow on minimal medium? If growth will occur, characterize the nature of growth relative to wild type.

What is the phenotypic effect of inserting a Ds element into the maize C gene? How do Ds and Ac produce maize kernels that are mostly yellow with purple spots?

Answer the following questions concerning the accuracy of DNA polymerase during replication.

What general mechanism do DNA polymerases use to check the accuracy of DNA replication and identify errors during replication?

Answer the following questions concerning the accuracy of DNA polymerase during replication.

If a DNA replication error is detected by DNA polymerase, how is it corrected?

Answer the following questions concerning the accuracy of DNA polymerase during replication.

If a replication error escapes detection and correction, what kind of abnormality is most likely to exist at the site of the replication error?

Answer the following questions concerning the accuracy of DNA polymerase during replication.

Identify two mechanisms that can correct the kind of abnormality resulting from the circumstances identified in part (c).

Answer the following questions concerning the accuracy of DNA polymerase during replication.

If the kind of abnormality identified in part (c) is not corrected before the next DNA replication cycle, what kind of mutation occurs?

Answer the following questions concerning the accuracy of DNA polymerase during replication.

DNA mismatch repair can accurately distinguish between the template strand and the newly replicated strand of a DNA duplex. What characteristic of DNA strands is used to make this distinction?

Several types of mutation are identified and described. These include (1) promoter mutation, (2) splice site mutation, (3) missense mutation, (4) frameshift mutation, and 5) nonsense mutation. Match the following mutation descriptions with the type(s) of mutations listed above. More than one mutation type might match a description.

A mutation that changes several amino acids in a protein and results in a protein that is shorter than the wild-type product.

Several types of mutation are identified and described in the chapter. These include (1) promoter mutation, (2) splice site mutation, (3) missense mutation, (4) frameshift mutation, and 5) nonsense mutation. Match the following mutation descriptions with the type(s) of mutations listed above. More than one mutation type might match a description.

A mutation that produces about 5% of the wild-type amount of an mRNA.

Several types of mutation are identified and described in the chapter. These include (1) promoter mutation, (2) splice site mutation, (3) missense mutation, (4) frameshift mutation, and 5) nonsense mutation. Match the following mutation descriptions with the type(s) of mutations listed above. More than one mutation type might match a description.

A mutation that produces a mutant protein that differs from the wild-type protein at one amino acid position.

Several types of mutation are identified and described in the chapter. These include (1) promoter mutation, (2) splice site mutation, (3) missense mutation, (4) frameshift mutation, and 5) nonsense mutation. Match the following mutation descriptions with the type(s) of mutations listed above. More than one mutation type might match a description.

A mutation that produces a protein that is shorter than the wild-type protein but does not have any amino acid changes in the portion produced.