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Modern Genetic Analysis Chapter 13. Transposable Genetic Elements
Problems

1. | Suppose that you want to determine whether a new mutation in the gal region of E. coli is the result of an insertion of DNA. Describe two physical experiments that would allow you to demonstrate the presence of an insertion.

2. | Explain the difference between the replicative and conservative modes of transposition. Briefly describe an experiment demonstrating each of these modes in prokaryotes.

3. | Describe the generation of multiple drug-resistance plasmids. See answer

4. | Briefly describe the experiment that demonstrates that the transposition of the Ty1 element in yeast takes place through an RNA intermediate.

5. | Explain how the properties of P elements in Drosophila make possible gene-transfer experiments in this organism. See answer

6. | When Rhoades took pollen from wholly pigmented anthers on plants of genotype a1 /a1 ; Dt /Dt and used this pollen to pollinate a1 /a1 ; dt /dt tested females, he found wholly pigmented kernels and, in addition, some dotted kernels. Explain the origin of both phenotypes.

7. | In Drosophila, M. Green found a singed allele (sn) with some unusual characteristics. Females homozygous for this X-linked allele have singed bristles, but they have numerous patches of sn+ (wild-type) bristles on their heads, thoraxes, and abdomens. When these flies are mated with sn males, some females give only singed progeny, but others give both singed and wild-type progeny in variable proportions. Explain these results.

8.

Crown gall tumors are found in many dicotyledonous plants infected by the bacterium Agrobacterium tumefaciens. The tumors are caused by the insertion of DNA from a large plasmid carried by the bacterium into the plant DNA. Suppose that a tobacco plant of type A (there are many types of tobacco plants) is infected, and it produces tumors. You remove tumor tissue and grow it on a synthetic medium. Some of these tumor cultures produce aerial shoots. You graft one of these shoots onto a normal tobacco plant of type B, and the graft grows to an apparently normal A-type shoot and flowers.
a. You remove cells from the graft and place them in synthetic medium, where they grow like tumor cells. Explain why the graft appears to be normal.
b. When seeds are produced by the graft, the resulting progeny are normal A-type plants. No trace of the inserted plasmid DNA remains. Propose a possible explanation for this "reversal."

See answer

9. | Consider two maize plants: a. Genotype C /cm ; Ac /Ac+ where cm is an unstable allele caused by Ds insertion b. Genotype C /cm, where cm is an unstable allele caused by Ac insertion What phenotypes would be produced and in what proportions when (1) each plant is crossed with a base-pair-substitution mutant cc and when (2) plant (a) is crossed with plant (b)? Assume that Ac and c are unlinked, that the chromosome breakage frequency is negligible, and that mutant c /C is Ac+.

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