In an assay for the presence of a specific disease gene allele in several individuals, you isolate genomic DNA from each and perform polymerase chain reaction (PCR) using gene-specific primers. The PCR product is expected to have a recognition site for the restriction endonuclease BamHI. Following PCR and BamHI digestion, the products are separated by gel electrophoresis and the results are shown in the figure below. Which lane corresponds to the individual demonstrating heterozygosity for the BamHI site?

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Quizplus · Accepted Answer

Someone who exhibits heterozygosity would harbor 2 distinct alelles. In the case of this analysis they would be identified as containing a copy of the gene that does not harbor the BamHI site and a copy that does harbor the site. The presence of the BamHI site in the PCR product in this example would result in the generation of 300 and 100 bp fragments. The lack of the site would yield a product of 400 bp. Thus, following PCR amplification and BamHI digestion of DNA from a heterozygote, one would be able to observe 3 bands of equal intensity.

In an Assay for the Presence of a Specific Disease