Thesis (M.Sc. (Med.))--University of the Witwatersrand, Faculty of Health Sciences, 1998. / The issue of Malagasy ancestry has been controversial, and has still not been
completely resolved. The historical, linguistic, archaeological and some genetic
evidence points to the fact that modern Malagasy are the descendants of immigrants
who arrived on the island over the past 2000 years, from South and Southeast Asia,
Africa and the Near East. In more recent centuries, mainly in the twentieth century,
there have been significant numbers of Indian, Chinese and French immigrants. In
addition, archaeological and historical studies of specific regional populations of
Malagasy suggest a complex pattern of internal migration within the island, extending
back in time to the first European contacts with the island in the sixteenth century. The
22 Malagasy ethnic groups may be classified as "highland" or "lowland" depending on
their geographic distribution on the island. Within the ethnic groups, the founding
populations have made different genetic contributions: the highland groups are said to
have a greater Indonesian contribution to their ancestry, while the lowlanders have a
greater African contribution to their ancestry.
Genetic studies on the Malagasy have been limited by small sample sizes, deficiencies
in sampling procedures and in the limited number of polymorphisms studied. In light of
the paucity of written records, the Department of Human Genetics, SAIMR, has
undertaken a large study in Madagascar to reconstruct the biological history of its
people, using genetic variation. This thesis forms a part of this study.
Variation in the a- and p-globin cluster has been extensively studied in many parts of
the world, and has been shown to be population specific, with specific variants having
distinct geographical distributions. Thus haemoglobin and its related disorders have
been the subject of extensive studies for determining the origin(s) of particular
populations. In this study, some of the a- and p-globin variation present in the Malagasy
was characterised. Seven RFLPs/HVRs in the a-globin gene cluster and seven RFLPs
in the p-globin gene cluster were analysed. The common a- and p-globin gene cluster
haplotypes differ between African and Asian populations. Frequencies also vary
between populations in a specific geographical regions. The aim of this study was to
characterise the haplotypes present in the Malagasy, to provide information on the
relative genetic contributions of different populations to the peoples of Madagascar.
DNA samples from randomly selected, haematologically normal individuals were
analysed. Individuals were chosen from six Malagasy ethnic groups: two “highland”
populations (Merina and Betsileo), two “lowland" populations (Antasaka and Tsimiheti)
and two populations from the south-west of the island (Mahafaly and Vezo). The groups
chosen cover a broad range of Madagascar and thus provide some representation of
the Malagasy population as a whole. The number of individuals studied in each ethnic
group are as follows: Merina: 88; Betsileo: 78; Antasaka: 67; Tsimiheti: 67; Mahafaly:
26; Vezo: 25.
The frequencies of the a- and (B-globin RFLP sites and a-globin HVRs in the Malagasy
vere calculated. 5' and 3’ p-globin haplotypes were constructed on the basis of
homozygosity. A maximum-likelihood algorithm was used to obtain frequencies of 5’
P-globin haplotypes that could not be assigned on the basis of homozygosity. These
data were then subject to statistical analysis. The frequencies of the 5’ p-globin
haplotypes (consisting of the five sites Hindi 5' to e, Hindi 11 within Gy and Ay, Hindi
within \|/P and 3' to it) were the most informative data set for comparing the Malagasy
ethnic groups to each other and to other world populations. Unfortunately, the
maximum-likelihood estimates of 5‘ p-globin haplotypes could not be used for
comparative analyses due to the lack of similar data in other populations. However
the strong correlation between the maximum-likelihood frequencies and the
observed frequencies illustrated the ability of the algorithm to determine hapiotype
frequencies from otherwise uninformative individuals.
5’ p-globin haplotypes were assigned unambiguously for 248 Malagasy
chromosomes. Ten haplotypes were found; of these, nine have been reported
previously in other world populations and one has not been reported and hns thus
been called “rare” in this study. The frequencies of unambiguous 5’ p-globin
haplotypes in the Malagasy and the proposed parental populations were initially
analysed with x2 tests. For a more accurate comparison between these
populations, genetic distances were calculated and used for the construction of
phylogenetic trees, principle component analysis was carried out, and a study of
heterozygosity versus distance from the centroid was performed. Admixture
estimates of two African populations and one Indonesian population to Malagasy
ancestry were calculated.
Certain general trends were noted in all the analyses. The results are in agreement
with the historical data which provides evidence for both African and Asian
contributions to Malagasy ancestry. The highlanders were more closely affiliated to
the Indonesian/Polynesian populations, while the south-west groups showed the
strongest associations with the African populations. The lowlanders were
consistently intermediate in position between the highlanders and the south-west
groups, with the Antasaka being slightly more closely related to the African
populations than the Tsimiheti. The Malagasy were shown to have high
heterozygosities, similar to those of African populations, and this high degree of
diversity is probably a reflection of the many sources of ancestry of the Malagasy.
The south-west groups were the furthest outliers in the model of heterozygosity
versus distance from the centroid, suggesting that these groups are the most
genetically admixed of all the Malagasy groups that were studied. Estimates of
ancestral population admixture confirmed these trends, with the highlanders having
the highest proportional contribution by Indonesians (53%), but the lowest total
African contribution (47%), while the south-west groups have the highest Bantu
contribution (65%). The Indonesian and African contributions to the lowlanders are
intermediate between those to highlanders and south-west groups. Overall the
Malagasy subjects included in this study showed a 61% African admixture
contribution and a 39% Indonesian admixture contribution.
It is hoped that the results obtained in this study will contribute to the larger project
concerning the origins of the Malagasy, and that they may be used to shed further
light on the much debated issue of Malagasy ancestry.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/14511 |
| Date | 07 April 2014 |
| Creators | Hewitt, Rachel |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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