Abban, Edward Kofi
(2023)
Genetic profiling of five major Ghana population
using Short Tandem Repeat and mitochondrial DNA
sequences for forensic and ancestry study purposes.
PhD thesis, Universiti Sains Malaysia.
Abstract
Population datasets of forensically relevant short tandem repeat (STR) and
mitochondrial DNA (mtDNA) from a particular population group are needed before any
DNA profile test results can be reliably submitted into evidence before the court. These
population datasets are proven useful for calculating match probabilities in forensic or
disputed paternity cases and for population genetic studies. However, autosomal and
Y-chromosome STR and mtDNA sequence datasets for representative African
populations, including Ghana, are lacking compared with European and Asian
populations. Therefore, the present study is conducted to provide the first-ever STR and
mtDNA population datasets that were screened from the same set of individuals
representing the Akans, Ewe, Ga-Dangbe, Mole-Dagbon and Guang sub-populations in
Ghana. Twenty-one autosomal STR loci in 515 genomic samples of these subpopulation
groups were typed using Investigator 24plex PCR amplification kit. The
match probability of identity ranged from 1 in 1.30x10-25 to 6.28x10-26, and the
combined power of discrimination ranged from 0.9999999999468 to
0.9999999999864. Genetic distances, phylogenetic tree and principal coordinate
analysis (PCoA) revealed that the five populations are genetically closer to each other
and neighbouring populations than distant localities. Unrelated males (n=268) were
then genetically characterized for 23 Y-chromosome STR loci using Powerplex Y23
STR kit. The haplotype diversity, discriminating capacity and match probability for the
pooled population data were 0.9998, 0.9627 and 0.0039, respectively. The pairwise genetic distance (RST) for the Ghanaian datasets and other reference populations
deposited in Y-STR Haplotype Reference Database were estimated and mapped using
multidimensional scaling (MDS) plot. The Guan and Ewe were significantly different
from the Akan, Mole-Dagbon and Ga-Dangme, but were all plotted closely with
reference African populations in the MDS data mapping. The entire mtDNA control
region in 207 unrelated individuals of the five major sub-populations of Ghana were
obtained using Sanger sequencing method. Results showed an admixture of mtDNA
types derived mainly from Africans (97.59%) and a minor proportion from Asians
(0.48%) and Europeans (1.93%). A high value of genetic diversity (0.9994), power of
discrimination (0.9991) and low value of random match probability (0.054) indicate
that mtDNA analysis for this population can effectively be used for forensic casework.
The most frequent mtDNA lineages were L (97.59%) and followed by U (1.45), N
(0.48) and X (0.48), and Ghanaian sub-populations are closer to West African
populations in PCoA data mapping. Overall, the present study has successfully typed
and developed STR and mtDNA datasets for the five sub-population groups in Ghana.
The statistical results showed that both markers are reliable for forensic DNA profiling
purposes and for studying genetic makeup in Ghana. Future studies should focus on the
other aspects of DNA profiling, such as validating newly DNA extraction and
genotyping kits and developing population data (STR, mtDNA or other potentially
relevant markers) for the remaining uncharacterized population groups in Ghana.
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