Susie DelRio, Deborah DiPierro, Amy Hayden and Kevin C. McElfresh
The Bode Technology Group, Sterling, VA

× Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø

The D-Loop of the mitochondrial DNA (mtDNA) contains numerous polymorphic sites within two regions designated HV1 and HV2. The mitochondrial genome is circular and approximately 16.5 kb in length with the HV1 and HV2 regions spanning the origin of replication (16200 bp to 405 bp). The highly polymorphic nature of the D-Loop region and the fact that there are several hundred copies of the mtDNA genome per cell have made the analysis of the mtDNA D-Loop region an important part of DNA based forensic identification. As with any genetic system used for forensic identification, validation studies must be done to determine the extent of the total variation and the factors that influence the genetic variation, most especially ethnic origin. The intent of this study was to quantify the total variation with the HV1 and HV2 regions of Caucasians, African Americans, Hispanics and Asians. The results were compared both within and between populations. The Anderson sequence was used as the standard sequence.

Results from our studies are consistent with the results of others that show that the most polymorphic mtDNA sequences are generally those in the African derived populations. For example, in this study, the African American sequences for HV1 had an average of 7 nucleotide substitutions per sequence (1.82%) while the Caucasian sequences had, on average, 2 nucleotide substitutions per sequence (0.48%). The Hispanic and Asian data fell between these two extremes. In the HV2 region, the Caucasian data had approximately 1 substitution per sequence, while the African American data had 8 substitutions per sequence.

We also identified a number of nucleotide substitutions that were ubiquitous in the non-Caucasian populations and in very low frequency in the Caucasian populations. For example, at nucleotide 73 in the HV2 regions, there was an A to G substitution that was virtually fixed in non-Caucasian populations and in a frequency of less than 15% in the Caucasian population. Several Caucasian sequences were identical to the Anderson sequence in the HV2 region, while so far, none of the African American sequences have been the same as the Anderson sequence.

When the mtDNA is combined with data from the nuclear genome for forensic identification purposes, the entire sequence for both the HV1 and HV2 regions is considered to be one type and the frequency calculated as if the type were a single allele.