Opinion ID: 1506658
Heading Depth: 1
Heading Rank: 38

Heading: The Dot-Intensity or Association-of-Alleles Technique

Text: In addition to his general objection to the polymarker test, defendant contends that the polymarker test cannot accurately analyze a mixed-blood sample. At trial, the experts described this method of analysis of interpreting the polymarker test on a mixed-blood sample as involving the association of alleles. Scientific articles describe it as dot-intensity analysis, a description that we adopt generally in this opinion. At the pretrial hearing, Dr. Word, one of the State's experts, testified that the polymarker test is designed so that if a single blood source contributes a pair of heterozygous alleles (i.e., A, B or B, C but not A, A), the two alleles will turn blue in equal intensities. If, however, two or more blood donors contribute the same allele, that dot would be more intense or a darker blue than if an individual donor contributed only one such allele. The same result would follow if one blood donor contributed two of the same allele so as to result in a pair of homozygous alleles (i.e., A, A or B, B but not A, B). In sum, the determination whether a sample is from more than one source of blood depends on the intensity of the color of the dots. Cellmark performed PM tests on three samples: (1) on a bloody towel, assumed to contain blood from the victim only; (2) on a sample of defendant's blood; and (3) from a portion of the box-spring cover that contained a mixture of blood. The polymarker test on the blood removed from the box spring revealed the presence of both possible alleles (A and B) for LDLR, GYPA, and D7S8, and all three possible alleles (A, B, and C) for HBGG and GC. An individual can possess, at most, two different alleles. Consequently, the presence of three different alleles at the HBGG and GC loci demonstrated that the DNA sample from the box spring was a mixture of blood from more than one individual. Dr. Word testified that the PM test conducted on the mixed-blood sample from the box spring revealed two distinct sources. Two sets of alleles caused the color imbalances in the dots from the box-spring sample. On the test strip, some of the blue dots appeared darker, but others were lighter. None of the dots, however, was lighter than the control dot. Those dot-intensity imbalances resulted from the presence of some alleles in pairs and other singly. Using dot-intensity analysis, Dr. Word explained that a theoretical subtraction of the victim's blood from the PM results of the box-spring sample revealed the genotype of the second subject. She explained that if all three alleles for GC were present (A, B, and C) and the A allele-dot was darker on the test strip, the sample contained two A alleles, one B allele, and one C allele. The genotypes of the contributing donors, then, had to be either AB and AC, or AA and BC. No other combinations consisted of two A alleles, and only one each of B and C. Based on dot-intensity analysis of the blood stain from the box spring, the State's experts concluded that the blood could have been a mixture of defendant's blood with that of Schnaps's. Cellmark made only two assumptions in its analysis: (1) that Schnaps was a donor to the blood on the box-spring sample; and (2) that the blood was a mixture of two people. The PM test for GC on the box spring revealed the presence of the A, B, and C alleles. The A dot was darker than the other two. That difference indicated that the composition of the GC in the sample consisted of two A alleles, plus the B and C alleles. If the sample had two donors, the possible combinations were AA and BC, or AB and AC. Schnaps was AC type for GC. The remaining donor therefore had to be AB. Defendant's genotype was AB. The D7S8 test on the box-spring sample revealed the A and B alleles, with the A dot being darker. The only possible combination, then, was AA and AB. Schnaps was AA type for D7S8. The remaining donor had to be AB. Defendant's genotype was AB. The HBGG test revealed the A, B, and C alleles at equal intensities. Because no dot was darker, Dr. Word testified that the possible combinations could be only AA and BC, AB and CC, or AC and BB. Schnaps was BB type for HBGG. Cellmark concluded that the remaining donor, then, had to be AC. Defendant's genotype was AC. The GYPA test revealed A and B alleles with the A dot being darker. Schnaps was AA type for GYPA. The other donor had to be AB. Defendant was AB. The LDLR test revealed A and B alleles with the B dot being darker. Schnaps was AB type for LDLR. The other donor had to be BB. Defendant's genotype for LDLR was BB. Based on those test results, the State's experts concluded that neither Harvey nor Schnaps could be excluded as donors to the box-spring blood sample. As with the RFLP test, infra part IV.A.2., the second step involves analysis of population statistics. Our discussion of the statistics in the present case is at infra part VI.