Animation 15.2: DNA Testing

INTRODUCTION

Many techniques exist for testing whether a sample of DNA carries a mutation. In this animation, we explore the use of two different techniques for identifying whether an individual carries the sickle-cell allele of the β-globin gene.

One procedure is called allele-specific oligonucleotide hybridization. In allele-specific oligonucleotide hybridization, the binding of a probe to sample DNA indicates that a particular allele is present in the DNA.

The other procedure, DNA testing by allele-specific cleavage, uses restriction enzymes as diagnostic tools. Restriction enzymes are proteins that recognize and cut DNA at specific sequences. Allele-specific cleavage relies on the mutation in the disease allele either adding or eliminating a recognition site for a restriction enzyme.

CONCLUSION

Allele-specific oligonucleotide hybridization is a widely used test that allows researchers to distinguish between two alleles that differ by a single nucleotide. The oligonucleotide probes are created so that each type hybridizes to DNA from just one of the alleles. Another probe hybridizes to a second allele. The probes need to be perfectly matched to the alleles, because a single mismatch will prevent hybridization of the probe to the DNA.

DNA testing by allele-specific cleavage uses restriction enzymes as diagnostic tools. In the example of sickle-cell anemia, the mutation that causes the disease also eliminates an MstII recognition site from the mutated β-globin gene. For this reason, the allele-specific cleavage test can be used to determine a person's genotype. However, many mutations that cause disease do not affect the recognition sites of restriction enzymes, thereby limiting the use of this particular technique in diagnosing disease.

Textbook Reference: Key Concept 15.4 Genetic Screening Is Used to Detect Disease

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