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10.25 A cDNA library is made with mRNA isolated from liver tissue and the vector shown in Figure 10.4. When a cloned cDNA insert from that library is digested with the enzymes EcoRI (E), HindIII (H), and BamHI (B) (described in Table 8.1, p. 174), the restriction map shown in the following figure, part (a), is obtained. When this cDNA isused to screen a cDNA library made with mRNA frombrain tissue and the vector shown in Figure 10.4, three identical cDNAs with the restriction map shown in the following figure, part (b), are obtained. When a uniformlylabeled, 32P-labeled riboprobe made using T7 RNA polymeraseis prepared using either cDNA and the probe is allowed to hybridize to a Southern blot prepared fromgenomic DNA digested singly with the enzymes EcoRI, HindIII, and BamHI, an autoradiograph shows the pattern of bands in the following figure, part (c). When any of the -32P labeled riboprobes are used to probe a northern blotprepared with poly(A)+ mRNA isolated from liver and brain tissues, no signal is seen. However, when the samenorthern blot is probed with a uniformly labeled, -32P labeled probe is prepared using the random primer method (described in Box 10.1), the pattern of bands in part (d) of the figure is seen. Fully analyze these data and then answer the following questions:a. Do these cDNAs derive from the same gene?b. Why are different-sized bands seen on the northern blot?c. Why could hybridization signal be detected on the Southern blot but not on the northern blot when riboprobes were used? Why could hybridization signal be detected on the northern blot when a random-primed probe was used? (Hint: consider how these probes aremade and which nucleic acid strands become labeled.)d. Why do the cDNAs have different restriction maps?e. Why are some of the bands seen on the whole genome Southern blot different sizes than some of the restriction fragments in the cDNAs?

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