Abstract:
The use of our hereditary material DNA as a biological tool has revolutionized
forensic investigations and population genetic studies and has led to the emergence of
molecular forensics and molecular anthropology. Analysis of polymorphisms in DNA enables
the identification of individuals and the determination of relationships between groups of
individuals with high degrees of sensitivity, accuracy and efficiency. The overall objectives of
this study were to facilitate the use of autosomal, Y-chromosomal and mitochondrial DNA
(mtDNA) markers in forensic case work and population genetics to identify individuals and to
determine genetic affinities of Sri Lankan population groups.
A total of 648 unrelated individuals belonging to five Sri Lankan populations viz.
Sinhalese, Sri Lankan Tamils, Indian Tamils, Moor and Veddahs (Adivasis) were sampled to
study polymorphisms in 11 autosomal and 12 Y-chromosomal STR loci and the
mitochondrial HVS1 locus.
The allele (or haplotype) frequency distributions, the heterozygosities (or gene
diversities) and polymorphisms of each loci tested in the above three DNA markers showed
that Sri Lankan ethnic groups (Sinhalese, Sri Lankan Tamils, Indian Tamils and Sri Lankan
moors) possess a relatively high genetic diversity, thus indicating the suitability of applying
those markers in forensic human identification. The autosomal STR results of the present
study have been successfully applied in more than 2600 paternity tests and 600 forensic cases
of human identification and the statistics described in this thesis have been used to interpret
DNA evidence submitted to Courts of Law in Sri Lanka.
Detailed phylogenetic analysis of the Sri Lankan populations using these three marker
sets revealed that the indigenous Adivasi population of Sri Lanka, who are considered to be
one of the “relic” population groups of early modem humans, forms a distinct cluster separate
from the other Sri Lankans. This suggests that they have experienced genetic drift, a
population bottle neck, or combination thereof. Their cryptic population structure and unique
allele signatures as revealed in the present study would make significant implications in
forensic investigations where Adivasi individuals are involved. The Adivasis possess
haplotypes that separate them from the rest of the Sri Lankans with multiple mutational steps
suggesting that they might be the surviving descendents of the earliest inhabitants of Sri
Lanka.
The suitability of using autosomal, Y-chromosomal and mtDNA markers for
discriminating between Sri Lankan individuals in DNA based forensic case work was
established. As a consequence of the development of databases for Y-STRs and mtHVSl
haplotype frequencies as well as the evaluation of applying and interpreting results in
casework as discussed herein, Y-chromosome and mitochondrial based human identification
can now be used as valuable additions to the current autosomal test panel to improve the
exclusion probabilities in forensic case work in Sri Lanka. In summary, Sri Lankan ethnic
groups possess considerable genetic homogeneity and are genetically similar to each other.
The observation that genetic differentiation among ethnic populations grouped by linguistic
affiliation was relatively higher than among populations delimited by ethnicity suggests
language has been a stronger barrier to gene flow than ethnic identity in Sri Lanka.