A deficiency in factor VIII causes hemophilia A, a blood disorder. Researchers s

Question

A deficiency in factor VIII causes hemophilia A, a blood disorder. Researchers studying hemophilia A evaluated the DNA from an affected patient and the patients unaffected mother. They analyzed the 186-kb-long factor VIII gene that includes 26 exons (See Chapter 14 in the textbook). After digesting the genomic DNA with Kpnl or Sstl and separating the products by gel electrophoresis, the researchers probed the DNA with a radiolabeled cDNA probe that binds the factor VIII gene in a region that includes exons 14-26. The size of the fragments and the corresponding exon(s) are shown on the right of autoradiograms. The researchers conclude that a transposon inserted into one of the exons of the factor VIII. E kb exon a E kb exon -30.0 (15-22) 19.1 (14) 21.0 (23-25) 12.7 (15-22) 7.3 (14) -8.3 (23-25) -5.5 (14) -5.3 (14) -4.3 (14) -4.0 (26) 3.2 (14)

Explanation / Answer

Exon 14 has two restriction sites for SstI. SstI digests the mother's DNA in such a manner that it produces 2 fragments of sizes 3.2 kb and 19.1 kb. In the patient, the insertion of the transposon has pushed the first restriction site further away, resulting in one larger fragment of size 5.5 kb and another of size same as mother (19.1 kb). The transposable insert is expected to be of 5.5-3.2 = 2.3 kb in size, and must lie in between the two restriction sites of SstI in exon 14.

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