You want to design a DNA probe used for hybridization to isolate a clone from a cDNA library. Which of the following concerns about DNA probe design is the most legitimate?
(a) You must be careful when designing your probe to take into account which DNA strand was transcribed in mRNA and choose a probe complementary to the mRNA.
(b) You must be careful not to include any DNA sequences in your probe that are upstream (5?) of the AUG start codon.
(c) You must make sure that all the DNA sequences in your probe lie within an exon, and do not span two exons.
(d) You must make sure that all the DNA sequences in your probe are not located downstream (3?) of the polyadenylation signal.
Choice (d) is correct. mRNAs are converted into cDNAs, which are double-stranded, so it is not necessary to worry about which strand the probe will hybridize with [choice (a)]. The transcriptional and translational start sites of an mRNA molecule differ, so including some sequences 5′ of the AUG start codon is not necessarily a problem [choice (b)]. Because cDNAs are made from mRNAs, the exon-splicing events have already occurred so it shouldn't matter if your probe sequences span two exons or lie within a single exon [choice (c)].
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A. true B. false
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a. foot b. mantle c. visceral mass d. head e. radula
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features? a. foot b. radula c. mantle d. shells e. visceral mass