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Modern Genetic Analysis Answers to Selected Problems
Chapter 14*

2. | Oc mutants are changes in the DNA sequence of the operator that impair the binding of the lac repressor. Therefore, the lac operon associated with the Oc operator cannot be turned off. Because an operator controls only the genes on the same DNA strand, it is cis (on the same strand) and dominant (cannot be turned off). See question

4. | See question

7. | A gene is turned off, or inactivated, by the "modulator" (usually called a repressor) in negative control, and the repressor must be removed for transcription to occur. A gene is turned on by the "modulator" (usually called an activator) in positive control, and the activator must be added or converted into an active form for transcription to occur. See question

10.

Bacterial operons contain a promoter region that extends approximately 35 bases upstream of the site where transcription is initiated. Within this region is the promoter. Activators and repressors, both of which are trans-acting proteins that bind to the promoter region, regulate transcription of associated genes in cis only.

The eukaryotic gene has the same basic organization. However, the promoter region is somewhat larger. In addition, enhancers as far as several thousand nucleotides upstream or downstream can influence the rate of transcription. A major difference is that eukaryotes have not been demonstrated to have polycistronic messages.

See question

13. | Construct a set of reporter genes with the promoter region, the introns, and the region 3 to the transcription unit of the gene in question containing different alterations that do not disrupt transcription or processing. Use these reporter genes to make transgenic animals by germ-line transformation. Assay for expression of the reporter gene in various tissues and the kidneys of both sexes. See question

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