Review Question - QID 214521

The test performed for genetic testing is most likely a restriction digest and agarose gel electrophoresis, which distinguishes individuals based on the variation in their restriction sites known as restriction length polymorphism.

Restriction enzymes are endonucleases that cut DNA strands in between conserved restriction sites. For example, the BamHI enzyme recognizes the sequence GGATCC and cuts inside that sequence. Sporadic mutations over time between individuals lead to the creation of new restriction sites and the destruction of other sites. Therefore, after digesting DNA with restriction enzymes, individuals will vary in terms of the length of DNA between available restriction sites. This variation in DNA length between sites is known as restriction length polymorphism, and this property serves as the cornerstone of DNA identity testing.

Incorrect Answers:
Answer 1: Copy number variation in certain genes describes how individuals may have varying numbers of different genes. For example, the alpha-amylase gene increases in copy number with populations that consume high starch diets. Though these vary at the population level, there is not sufficient variation between individuals for this to be a definitive method of genetic testing.

Answer 2: Differential expression of restriction enzymes is not relevant for the test being described. In genetic testing, standardized and purified restriction enzymes primarily from bacteria are added to human genetic material in order to generate fragments of DNA. Therefore, the restriction enzymes being used for every individual are the same.

Answer 3: Protein abundance variation may occur due to epigenetic modification of the genome. For example, endurance athletes may express higher levels of oxidative enzymes compared with sedentary individuals; however, protein abundance depends too much on environmental factors for it to be useful in identity testing.

Answer 5: Trinucleotide repeat polymorphism occurs in diseases such as Huntington disease. These repeats increase in number with every generation such that each subsequent generations will develop disease earlier than the previous generation. These repeats have no value in identity testing.

Bullet Summary:
Restriction length polymorphism describes how DNA from different individuals will have a unique pattern of bands when digested with restriction enzymes.