Nearly 1. half the human genome consists of DNA that can be classified by sequence as transposable elements, yet many of these sequences are incapable of moving throughout the genome. This is best attributed to:
(a) Lack of any transposon sequence encoding reverse transcriptase in the human genome. (b) Accumulation of mutations in transposon-derived sequences that has rendered the sequences no longer functional. (c) Now that modern humans have evolved, the genome will no longer tolerate change. (d) All human transposons originated as retroviruses, but without the original parent virus present, no transposon movement can occur.
Answer: B
2. What is the most reasonable explanation for the observation that transposons in the human genome are more often found in nongenic sequences such as the centromere than in genic sequences?
(a) Insertion into nongenic DNA is less likely to have a negative phenotypic effect than insertion into genic DNA. (b) The AT-rich nature of centromere and other nongenic sequences makes it easier for transposon insertion. (c) Reverse transcriptase promotes integration into nongenic DNA preferentially. (d) Genic DNA is protected from transposon insertion by all the transcription factors bound to the region.
Answer: A 1
3. Transposable element insertion in human gene ORFs: (a) (b) (c) (d) (e) Is extremely common Is relatively rare Is more common than insertion into introns A and c B and c
Answer: B
4. Transposase is: (a) (b) (c) (d) (e) A protein A DNA sequence A mobile genetic element A and c B and c
Answer: A
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5. Which of the following types of transposition events in bacteria would be expected to increase the genome copy number of the transposon most rapidly? (a) (b) (c) (d) (e) Conservative transposition Cut and paste transposition Replicative transposition A and b B and c
Answer: C
6. A researcher would initiate a genetic screen using a transposon as a mutagen most likely because: a) Unlike other mutagens, transposons will not harm the recipient cell. b) The transposon will insert ubiquitously in nongenic DNA; the researcher can conclude that the remaining DNA is genic. c) The transposon may insert into a gene, resulting in a mutant phenotype and providing a molecular tag of the gene. d) Transposons are less toxic to work with than chemical mutagens.
Answer: C
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9. Which of the following statements are true? a) Ac elements and Ds elements have the same inverted repeat sequences. b) Ds elements have mutated inverted repeats, causing them to be incapable of selftransposition. c) Ac encodes a functional reverse transcriptase. d) Ac and Ds elements were first studied in E. coli. e) Ac encodes a functional transposase while Ds does not encode a functional transposase.
Answers: and a e
10. A maize plant is homozygous for an allele C m, caused by the insertion of a Ds element into the coding region of a gene (C) that encodes an enzyme necessary for the synthesis of anthocyanin color in maize kernels.
(i) If this plant also contains an Ac element in its genome, what will be the phenotype of its kernels? Spotted, colored or colorless?
(ii) If this plant does not contain an Ac element, what will be the kernel phenotype? Spotted, colored or colorless?
(iii) If the plant does not contain an Ac element, but it does contain an autonomous element for another family of transposon, what will be the kernel phenotype? Spotted, colored or colorless? 4
Answer: (i) spotted (the Ac element provides a transposase that can move the Ds element during kernel development).
(ii) colorless (no transposase = no movement = no restoration of color).
(iii) colorless (the transposase enzyme is family specific; similar to part (ii), there is no tranposase that can recognize and move elements of the Ac/Ds family).
11. P elements of Drosophila have been developed into a system for producing transgenic organisms. True or False
Answer: True
12. In the Gal4-UAS binary system of Drosophila, what can regulate the transcription of Gal4? a) Genomic enhancers near the insertion of the P element containing Gal4 b) The yeast UAS sequences c) The enhancer that the researcher placed into the P element 5' of the Gal4 coding region d) A and B e) A and C
Answer: E 5
13. In the Gal4-UAS binary system of Drosophila, what can bind to the UAS sequence?
Answer: Gal4 protein
14. In the Gal4-UAS binary system of Drosophila, what happens when Gal4 binds UAS? a) Nothing - Drosophila does not have UAS sequences b) The coding region next to UAS is transcribed c) Yeast infects the cells d) The w+ gene is activated e) B and C
Answer: B
15. In the Gal4-UAS binary system of Drosophila, what kinds of genes can be inserted next to UAS and expressed? a) protein encoding genes b) human genes c) microRNA genes d) any gene from any organism e) telomeres
Answer: D
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16. Give three examples of how to use the Gal4-UAS system
1. enhancer trap/detector
2. to overexpress a protein; or to misexpress a protein, e.g. express in a tissue where that protein would not normally be found
3. to test a protein's function, when the wild type, endogenous gene for that protein has been knocked out; e.g. test the human version of that protein, to see if it functions similarly enough to rescue the fly mutant phenotype
4. can also put in a mutated form of a protein (in the knockout background), to see what effect it has. In this way, have control over exactly what the mutation is (because you engineered it in the lab)
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