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Modern Genetic Analysis Answers to Selected Problems
Chapter 13*

3. | R plasmids are the main carriers of drug resistance. They acquire these genes by transposition of drug-resistance genes located between IR (inverted repeat) sequences. Once in a plasmid, the transposon carrying drug resistance can be transferred upon conjugation if it stays in the R plasmid, or it can insert into the host chromosome. See question

5. | P elements are transposons (genes flanked by inverted repeats, allowing for great mobility). Because they are transposons, they can insert into chromosomes. By inserting specific DNA between the inverted repeats of the P elements and injecting the altered transposons into cells, a high frequency of gene transfer will occur. See question

8.

a. The expression of the tumor is blocked in plant B. This suggests either that plant B can suppress the functioning of the plasmid that causes the tumor, or that plant A provides something to the tissue with the tumor-causing plasmid that plant B does not provide.
b. Tissue carrying the plasmid, when grafted to plant B, appears normal, but the graft produces tumor cells in synthetic medium. This indicates that the plasmid sequences are present and capable of functioning in the right environment. However, the production of normal type A plants from seeds from the graft suggests a permanent loss of the plasmid during meiosis.
See question

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