The modular nature of the Eve gene's regulatory region means that ______
(a) there are seven regulatory elements and each element is sufficient for driving expression in a single stripe.
(b) all the regulatory elements for each stripe use the same transcriptional activators.
(c) the E. coli LacZ gene is normally only expressed in a single stripe—unlike Eve, which is expressed in seven stripes.
(d) transcription regulators only bind to the stripe 2 regulatory DNA segment in stripe 2.
Choice (a) is correct. Different transcriptional activators are located in different regions of the Drosophila embryo and are differentially responsible for expression in different stripes [choice (b)]. The E. coli LacZ gene is a reporter gene and is not normally expressed in flies; its expression depends on the specific regulatory element engineered into its promoter [choice (c)]. In other stripes, transcriptional repressors may bind to the stripe 2 regulatory DNA segment while transcriptional activators will bind to this segment in stripe 2 [choice (d)].
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