Reading:

• Principles of Genetics, Snustad & Simmons 2012: Chapter 13
• DNA is Constantly Changing through the Process of Mutation
• Loewe, L. (2008) Genetic mutation. Nature Education 1(1)

Video (Orient yourself to basics of mutation by watching these videos):

Professor Anderson's Mutation Video

Damage to DNA Leads to Mutation

Lab Exercise

Go to website on Mutations are Changes in Genetic Information Explore the Concept, Animation (be sure to follow the arrows to view all the screens), Video pages. Answer the following questions:

1. Describe the experiments of Hermann Muller (use this lab website including the videos of Elof Carlson, Chapter 13 in text reading, and other resources). (Describe the experiments in detail using summarizing and citing the different resources you researched (~300 words).

2. What did these experiments of Hermann Muller demonstrate? Why were these experiments important to the study of genetics?

3. Under the Problem tab of this website identify the number of point mutations between humans and chimpanzees. Take a screenshot of the highlighted differences and paste the image here. How many nucleotide differences were there between humans and chimpanzees in the 379-nucleotide part of the mt control region?

Lab Problems

4. List all possible missense mutations that can occur in a segment of DNA encoding the amino acid tryptophan. What is the ratio of transversions to transitions if all single base-pair substitutions occur at the same frequency?

5. How can mutations in bacteria causing resistance to a particular drug be detected? How can it be determined whether a particular drug causes mutations or merely identifies mutations already present in the organisms under investigation? Answer these questions in terms of experimental procedures.

6. The bacteriophage T4 genome contains about 50 percent A:T base pairs and 50 percent G:C base pairs. The base analog 2-aminopurine induces A:T -> G:C and G:C -> A:T base-pair substitutions by undergoing tautomeric shifts. Hydroxylamine is a mutagenic chemical that reacts specifically with cytosine and induces only G:C -> A:T substitutions. If a large number of independent mutations were produced in bacteriophage T4 by treatment with 2-aminopurine, what percentage of these mutations should you expect to be induced to mutate back to the wild-type genotype by treatment with hydroxylamine? Explain your answer.

7. You are screening three new pesticides for potential mutagenicity using the Ames test. Two his? strains resulting from either a frameshift or a transition mutation were used and produced the following results (number of revertant colonies):

What type of mutations, if any, do the three pesticides induce?

8. The wild-type sequence of part of a protein is

NH2-Trp-Trp-Trp-Met-Arg-Glu-Trp-Thr-Met

Each mutant in the following table differs from wild type by a single point mutation. Using this information, determine the mRNA sequence coding for the wild-type polypeptide. If there is more than one possible nucleotide, list all possibilities.

Mutant Amino Acid Sequence of Polypeptide 1 Trp-Trp-Trp Met 2 Trp-Trp-Trp-Met-Arg-Asp-Trp-Thr-Met 3 Trp-Trp-Trp-Met-Arg-Lys-Trp-Thr-Met 4 Trp-Trp-Trp-Met-Arg-Glu-Trp-Met-Met

9. Acridine dyes such as proflavin are known to induce primarily single base-pair additions and deletions. Suppose that the wild-type nucleotide sequence in the mRNA produced from a gene is 5?-AUGCCCUUUGGGAAAGGGUUUCCCUAA-3? Also, assume that a mutation is induced within this gene by proflavin and, subsequently, a revertant of this mutation is similarly induced with proflavin and shown to result from a second-site suppressor mutation within the same gene. If the amino acid sequence of the polypeptide encoded by this gene in the revertant (double mutant) strain is NH2-Met-Pro-Phe-Gly-Glu-Arg-Phe-Pro-COOH

What would be the most likely nucleotide sequence in the mRNA of this gene in the revertant (double mutant)?

10. Which of the following amino acid substitutions should you expect to be induced by 5-bromouracil with the highest frequency? (a) Met -> Leu; (b) Met -> Thr; (c) Lys -> Thr; (d) Lys -> Gln; (e) Pro -> Arg; or (f) Pro -> Gln? Why?