Opinion ID: 2600593
Heading Depth: 6
Heading Rank: 2

Heading: Swabs from Tahisha's body

Text: Criminalist Lough collected evidence from Tahisha's body, including swabs of the inside and outside of her vagina, as well as a rectal swab. Lough began testing the swabs on April 27, before any sample of blood from defendant had been submitted to the crime laboratory. Lough's testing detected the presence of saliva on the outer genital area. Further testing indicated that the person whose saliva was found on Tahisha's body had ABO type A blood. Tahisha had ABO type O blood, which excluded her as the source of the saliva. Defendant is among those persons comprising approximately 30 percent of the population who have ABO type A blood. Criminalist David Stockwell subsequently performed DNA testing on the external vaginal swab. He found DNA that was consistent with Tahisha's DNA, and also DNA from another person. The three genetic markers that were inconsistent with Tahisha's DNA were consistent with defendant's DNA. [9] These markers appear on different chromosomes, and thus are independently inherited; that is, whether a person inherits one protein has no relation to whether that person inherits another protein. Stockwell testified that the frequency of individuals having the same genetic markers as found in the DNA that was foreign to Tahisha is approximately one in 400,000. Criminalist Donald Jones analyzed the internal vaginal swab and the rectal swab using a technique known as restriction fragment length polymorphism, or RFLP. The RFLP procedure employs an enzyme that recognizes certain sequences of DNA and severs or restricts the DNA in certain locations. The length of particular sequences of DNA will vary among individuals. Therefore, the RFLP test may establish that DNA from more than one individual is present by revealing different lengths of the selected sequences of DNA, and may establish whether the foreign DNA is consistent or inconsistent with a particular foreign donor. Because the internal swabs were collected from parts of the body that slough off epithelial cells, these swabs contained large amounts of Tahisha's DNA. Lough had suggested to Jones that these swabs also might contain foreign DNA from saliva. Therefore, Jones had the task of attempting to identify any foreign epithelial cells shed from the mouth in saliva, amidst a much larger quantity of epithelial cells from the victim. In attempting to maximize the amount of any foreign DNA in the tested sample, Jones used 10 to 12 times the amount of sample that normally is tested. Jones's RFLP test generated results that reflected the presence of Tahisha's DNA, as well as some sequences of DNA that were different lengths from the sequences of Tahisha's DNA. Jones testified that overloading of the sample may have resulted in a higher incidence of partially digested DNA sequences that were not severed at the proper site on the DNA and therefore were a different length. In Jones's opinion, the sequences of DNA that were a different length from Tahisha's DNA were partial digests rather than foreign DNA. Although Jones concluded that the sequences that were of a different length from Tahisha's DNA were due to partial digests, he also testified that such sequences could result from foreign DNA or from bacterial DNA present in the body; if they were the result of foreign DNA, they were not the product of defendant's DNA.