Multi-Locus and Single-Locus DNA Profiling in New Zealand

Abstract

The New Zealand population can be subdivided into four major ethnic groups; Asian, Caucasian, Polynesian and Maori. DNA samples from individuals in the four groups were analysed using multi-locus minisatellite DNA probes 33.15 and α-globin 3'HVR. Probe 33.15 was validated for forensic "DNA profiling" in the New Zealand population. There is no significant variation in either the number of bands or the level of band sharing between individuals for any ethnic group using probe 33.15. Exclusion probabilities can therefore be calculated without ethnic bias. Technical difficulties were experienced using the α-globin 3'HVR probe, and it was found to have much lower discriminating power than previously claimed. It is, therefore, not recommended for forensic use. Allele frequency distributions were obtained for three VNTR loci; D12S11, D4S139 and D2S44 using restriction endonuclease HinfI and for four other loci: D2S44, D14S13, D14S1 and D17S79 using PstI. Intergroup variation in allele frequency spectra was measured using Pearson Chi-Squared and two-sided Kolmogorov-Smirnov goodness-of-fit tests. In general, spectra for Maori and Polynesian exhibited the most similarity. The HinfI database was investigated for the occurrence of pseudohomozygous phenotypes caused by coalescence of bands and undetected alleles. The small excess of homozygotes over expected at the D12S11 locus found in Maori and Polynesian ethnic groups can be attributed to coalescence of high molecular weight alleles. Some small alleles at locus D4S139 were shown to be lost during electrophoresis. VNTR genotype frequencies in Maori and Polynesians were found to deviate from Hardy-Weinberg expectations, but the mechanisms underlying this deviation were attributable to coalescence rather than to genetic subdivision. The database as a whole shows an artefactual Wahlund effect at loci Dl2S11 and D4S139, which is caused by combining allele frequency data from genetically distinct ethnic groups. All VNTR loci show local independence of alleles, justifying the use of the product rule to calculate exclusion probabilities for casework, if a demographically stratified database is used. The allele distributions at D12S11 and D2S44 were found to fit the predictions of the infinite alleles model of neutral evolution. Lowered gene diversity for Maori and Polynesian groups at these loci support previous claims of a general reduction in diversity due to repeated genetic bottlenecks during the colonisation of the South Pacific. The Maori however, did not show evidence of further reduction in genetic diversity, beyond that observed in Polynesians. DNA profiling is a powerful technique for forensic identification, which has been subjected to unprecedented scrutiny in New Zealand. In this study, all procedures for analysis and the reporting of results from DNA profiling used by forensic scientists in this country have been validated for its population.