Peng, Hoh Boon
(2009)
Geenetic relationship among the negrito
(Semang) tribes of peninsular Malaysia:
the microsatellite approach.
Geenetic relationship among the negrito (Semang) tribes of peninsular Malaysia: the microsatellite approach.
Abstract
One of the approaches to identify susceptibility genes for complex disorders is to focus
on genetically isolated populations such as the Orang Asli populations rather than the
general population, because the environmental variation may be lower and the genetic
make-up of these populations is expected to be less complex. Various markers have been
used for genetic linkage mapping. Microsatellite markers are of interest to many
researchers as they are more polymorphic and hence more informative (typically having
more than ten alleles). Hence, they offer greater statistical power for the data analysis,
whether by parametric analysis of large families, or nonparametric analysis of sib-pairs
etc. The Negritos (Semang}, believed as the first Orang Asli group to arrive in Peninsular
Malaysia more than 10,000 years ago. They are divided into six subgroups, namely,
Kensiu, Bateq, Mendriq, Jahai, Lanoh and Kintak. Therefore, studying this ethnic group
could be useful for fine scale mapping as well as better understanding for the
evolutionary and biological process leading to certain disease.
The objective of the study is to generate the genotype data of 10 selected microsatellite
markers among the 3 Negrito tribes in Kelantan state, and later to compare the allele
frequencies with other ethnic groups from publicly available data. 10 markers with the
highest heterozygosities were chosen (Appendix I) and seven were applied. The observed
heterozygosities of the seven loci were found to be significantly lower than those found
in the published database, except for DlS243, suggesting the possibility of inbreeding
and genetic drift in the Negrito population. A larger scale investigation using more
samples and markers should be done to confirm the results. Such study would also help in
our understanding of pre-historic human migration in the Malay Archipelago which until
today remains largely a mystery besides providing information for forensic profiling and
the identification of complex diseases which may be prevalent in certain populations.
Comprehensive Technical Report
Official consent was obtained from the JHEOA and the discrict representative
respectively. Samples were collected from Pos Lebir, Kuala Lar, Sg Rual and Aring. A
total of 105 samples were collected. However, only 62 were included into the study after
a stringent sample inclusion criteria. This includes 18 Bateqs, 14 Mendriqs and 30 Jahais.
The numbers of individuals in the tribes are decreasing and majority of them practice
consanguineous marriage, or inter-tribe marriage. Currently, there are about 1000
individuals in the Jahai tribe; 700 in Bateq tribe; and less than 80 individuals in Mendriq
tribe. Thus, it is of reasonable that the sample collection is rather lesser than that of
expected.
I 0 markers with the highest heterozygosities were chosen (Appendix I). Optimizations
were done and 7 of the primers were successful. These markers were amplified on the
samples and the fluorescent-labeled fragments were electrophoresed through ABB I 00
and analyzed using GeneScan analysis software. The allele frequencies of the loci were
calculated. Heterozygosities of the markers and possible error in genotyping or allele
calling were checked and tested with Hardy-Weinberg's Equilibrium. Due to time
'·
constraint, the remaining SIR primers were not further optimized.
The observed heterozygosities of the seven loci were found to be significantly lower than
those found in the published database, except for DI 8243. The lower observed
heterozygosity among the Negritos compared to other published data suggested the
possibility of inbreeding and genetic drift in the Negrito population in general. Analysis
with a low value of Fst (0.0694) indicating the high genetic similarity among the three
tribes, supported the suggestion; while the number of individuals in the tribes further
proven the findings in this study.
If carried out using sufficient sample sizes and loci, a study such as this would be helpful
in understanding pre-historic human migrations in the Malay Archipelago which
currently remains largely unknown. On top of that, it may contribute additional
information to forensic profiling and the identification of complex diseases which may be
prevalent in certain populations.
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