17. Mutation, Repair, and Recombination

Ultraviolet (UV) radiation is mutagenic.

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

Ultraviolet (UV) radiation is mutagenic.

How do UV-induced DNA lesions lead to mutation?

Ultraviolet (UV) radiation is mutagenic.

What kind of DNA lesion does UV energy cause?

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.

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.

In 2013 the actress Angelina Jolie elected to have prophylactic double-mastectomy surgery to prevent breast cancer based on a positive test for mutation of the BRCA1 gene. What are some potential positive and negative consequences of this high-profile example of acting on the results of a genetic test?

Xeroderma pigmentosum (XP) is an autosomal recessive condition characterized by moderate to severe sensitivity to ultraviolet (UV) light. Patients develop multiple skin lesions on UV-exposed skin, and skin cancers often develop as a result. XP is caused by deficient repair of DNA damage from UV exposure.

A series of 10 skin-cell lines was grown from different XP patients. Cells from these lines were fused, and the heterokaryons were tested for genetic complementation by assaying their ability to repair DNA damage caused by a moderate amount of UV exposure. In the table below, '+' indicates that the fusion cell line performs normal DNA damage mutation repair, and '−' indicates defective DNA repair. Use this information to determine how many DNA-repair genes are mutated in the 10 cell lines, and identify which cell lines share the same mutated genes. 

In 2010, a U.S. District Judge ruled to invalidate Myriad Genetics' patents on the BRCA1 and BRCA2 genes. Judge Sweet noted that since the genes are part of the natural world, they are not patentable. Myriad Genetics also holds patents on the development of a direct-to-consumer test for the BRCA1 and BRCA2 genes.

J. Craig Venter has filed a patent application for his 'first-ever human-made life form.' This patent is designed to cover the genome of M. genitalium. Would your ruling for Venter's 'organism' be different from the judge's ruling on patenting of the BRCA1 and BRCA2 genes?

In 2010, a U.S. District Judge ruled to invalidate Myriad Genetics' patents on the BRCA1 and BRCA2 genes. Judge Sweet noted that since the genes are part of the natural world, they are not patentable. Myriad Genetics also holds patents on the development of a direct-to-consumer test for the BRCA1 and BRCA2 genes.

Would you agree with the ruling to invalidate the patenting of the BRCA1 and BRCA2 genes? If you were asked to judge the patenting of the direct-to-consumer test for the BRCA1 and BRCA2 genes, how would you rule?

Following the spill of a mixture of chemicals into a small pond, bacteria from the pond are tested and show an unusually high rate of mutation. A number of mutant cultures are grown from mutant colonies and treated with known mutagens to study the rate of reversion. Most of the mutant cultures show a significantly higher reversion rate when exposed to base analogs such as proflavin and 2-aminopurine. What does this suggest about the nature of the chemicals in the spill?