Mutations and defects in chromosomal structure January 2009

1. Mutations and defects in chromosomal structureJanuary 2009

2. Types of Mutations

3. How do most mutations arise? A. They are caused by environmental stress and are a response to it B. They are random events that can be caused by many different things C. They preprogrammed into the genome to occur in response to specific signals D. Mutations almost never happen because DNA can repair itself 3

4. What is a mutation? • A change in DNA sequence that causes a change in phenotype • A change in DNA sequence that is passed to a cell’s progeny • Any change in DNA sequence

5. How do mutations arise? Experiment: expose bacteria to bactericide; wild type cells do not survive, but there are some colonies on the plates. These colonies have mutations that allow them to grow on bactericide. How did the mutations arise? A) Exposure to bactericide causes mutations – creates cells that are resistant. B) Mutations happen randomly – some mutations just happen to make cells resistant to bactericide.

6. Luria-Delbruck Experiment • What do the results of this experiment mean? • Mutations are more frequent when cells are exposed to bactericide • Mutations likely occurred after exposure to the bactericide • Mutations likely occurred before exposure to the bactericide Random mutations likely occurred before the cells were exposed to bactericide. Some cells acquired mutations that allowed them to grow on bactericide.

7. If depurination occurs 1000 times/hour in humans, why don’t humans have more genetic diseases (mutations)? A) most of the mutations are in parts of the genome that are not transcribed to mRNA, so the mutations have little effect. B) most depurinations are fixed by DNA repair enzymes. C) most depurinations will occur in cells that are not part of the germline, so they will not cause disease. D) the redundancy of the genetic code will prevent the depurinations from changing the protein sequence and causing disease.

8. Which type of mutation is most likely to lead to the formation of a nonfunctional protein? • A silent mutation • A frame shift mutation • A missense mutation • All of the above will lead to nonfunctional proteins

9. A type of human dwarfism results from the production of mutant SHR-1 protein. You look at the length of the mutant SHR-1 and the normal (wild-type) SHR-1 protein, and discover that the mutant SHR-1 protein has fewer amino acids. What do you expect to find when you examine the DNA sequence? A. nucleotides were deleted B. additional nucleotides were added C. one nucleotide was changed D. without additional information, any of the above are possible

10. You are studying a gene called Ant-1. You discover an insertion of one nucleotide in a mutant Ant-1 gene. When you compare the wild-type Ant-1 protein and the mutant Ant-1 protein, you expect that: The wild-type Ant1 protein will be longer than the mutant Ant-1 protein The mutant Ant-1 protein will be longer than the wild-type Ant 1 protein The wild-type Ant-1 protein and the mutant Ant-1 protein will be the same length Answer A and B All of the above

11. ATG= Met GAG= Glu TGA =Stop GAA= Glu TAA= Stop CAA= Gln CAG = Gln The following DNA sequence corresponds to the two extreme ends of a gene’s coding regions: 5’ ATG-GAA//CAG-TGA 3’ Each codon is separated by a dash and the middle of the gene is represented by “//”. Referring to the codons listed above, which of the following sequence changes is likely to interfere most with the function of this gene? A. 5’ ATG-GAA//CAA-TGA 3’ B. 5’ ATG-TAA//CAG-TGA 3’ C. 5’ ATG-GAG//CAG-TGA 3’ D. (a.) and (b.) are equally likely to interfere with the function of this gene E. (b.) and (c.) are equally likely to interfere with the function of this gene

12. You have isolated a conditional mutation in Neurospora that has the following phenotype: At 30 degrees it can synthesize DNA, at 42 degrees no DNA is synthesized and the cells die. This mutation is most likely a a. Nonsense mutation b. Missense mutation c. Frameshift mutation

13. Let’s say you lived in a world where there was no physical (UV light and X-ray), and no chemical mutagens. Would your DNA undergo mutations? Yes No

14. You heard on the news that grilling steak can create carcinogens and cause cancer, so you decide to test the hypothesis with the Ames Test + control sodium azide a known carcinogen experimental – small piece of grilled steak - control no sample Are the colonies on the experimental plate likely to be revertants? A) yes B) no

15. You heard on the news that grilling steak can create carcinogens and cause cancer, so you decide to test the hypothesis with the Ames Test + control sodium azide a known carcinogen experimental – small piece of grilled steak - control no sample Are the colonies on the negative control plate likely to be revertants? A) yes B) no

16. Test substance + rat liver enzyme + distilled water 500 Test substance + distilled water 2 distilled water 10 rat liver enzymes 1 positive control 675 negative control 12 • The test substance is: • a mutagen • a mutagen, but only when metabolized • not a mutagen • can’t tell – there is contamination in the experiment

17. C A T C G C A T C G G T A G C Depurination G T A C C A T X G G T A C apurinic site C A T C G G T A G C • Depurination is the removal of a purine base. • After a depurination, how many (of the 4) replicated DNA strands • are likely to be mutant? • 1 • 2 • 3 • 4

18. When the mutation 21 is present, wild type protein no longer functions. This can explain the following mode of inheritance dominant (Aa or AA = disease) recessive (aa = disease)

19. Characterization of Mutants (complementation)

20. Study published Jan 8, 2008 Current Biology Journal • You study eye formation using Mexican cave-dwelling blind fish. You know that blindness is a trait controlled by multiple genes and inherited in a recessive manner. • A blindfish from a true-breeding line in one cave was crossed to a blind fish from a true-breeding line in another cave. If the mutation that cause blindness is in the same gene in two fish, you should see • A. None of the offspring are blind • B. 25% of the offspring are blind • C. 50% of the offspring are blind • D. 75% of the offspring are blind • E. All of the offspring are blind

21. You isolate 3 mutant strains of rII, labeled 1-3. You coinfect E. coli K12  with pairwise combinations (1&2, 1&3 etc.) of the 3 mutant strains and get the following results: How many genes did you mutate? 0 1 2 3 4

22. Oops, you just found another rII mutant strain on your laboratory bench. So you expand your complementation test to include the 4 mutant strains and get the following results: How many genes did you mutate? 0 1 2 3 4

23. Complementation DataNeurospora Auxotrophs (Haploids) Mated with Each Other and Plated on Minimal Plates 1 2 3 4 5 6 1 - + - - + + 2 - + + + + 3 - - + + 4 - + + 5 - + 6 - Strains 1-6 are all arg- auxotrophs, how many genes? • 1 • 2 • 3 • 4 • 5

24. CSU has hired you to generate green ram mascots. You mutate a bunch of rams and get 4 that are green because of recessive mutations. You carry out crosses between all the rams (all rams can mate with each other, don’t worry about mascot sex) and produce the following results where a "-" means mutant green rams were produced and a "+" means wild-type white rams were produced. Which statement is correct? 1 crossed with 3 will produce a green ram 1 crossed with 3 will produce a white ram

25. UNC has hired you to generate gold bear mascots. You mutate a bunch of bears and get 4 that are gold because of recessive mutations. You carry out crosses between all the bears (all bears can mate with each other, don’t worry about mascot sex) and produce the following results where a "-" means mutant gold bears were produced and a "+" means wild-type brown bears were produced. Which statement is correct? 1 crossed with 4 will produce a gold bear 1 crossed with 4 will produce a brown bear

26. phage assembly pathway Next, you want to determine how many different genes your mutants represent, so you perform a complementation test. Which is/are true in your complementation test? A) if the mutations of the parents are in the same gene, plaques will not form. B) If the mutations of the parents are in the same gene, plaques will form. C) if the mutations of the parents are in different genes, plaques will form. D) Both A and C are true. E) Both B and C are true.

27. Complementation Test Results 1 2 3 4 5 6 How many different genes do your 6 mutants represent? A) 6 C) 4 B) 5 D) 3

28. Complementation data can be presented in a grid: Here’s a grid for six strains showing the same mutant phenotype: 123456 1 - - + - - + + 2 - - + + + + 3 - - - + + 4 - - + + 5 - - - 6 - - How many complementation groups are there? A. 1 B. 2 C. 3 D. 4 E. 5

29. Chromosomal Structure Mutations(Translocations, inversions, and duplications)

30. Chromosome arrangement of the female translocation carrier Metaphase of meiosis I (homologues segregate) • Which color signals would represent balanced gametes produced by meiosis • of the above translocated chromosomes? • gamete 1: orange, (red and green) gamete 2: (orange and green), red • gamete1: orange, red gamete 2: (orange and green), (green and red) • gamete 1: red, (red and green) gamete 2: (orange and green), orange