May 17, 2005

Back-migration into Cameroon

The presence of R1* Y chromosomes in Cameroon is considered as evidence of a back migration from Eurasia into Sub-Saharan Africa. A new study of mtDNA in the region shows that Eurasian mtDNA is severely underrepresented, and hence either (i) there was biased male-mediated gene flow into the population, or (ii) the Eurasian mtDNA was lost due to drift.

An alternative explanation, not considered by the authors is that mtDNA, known to be involved in energy production, is subject to strong selection in different natural environments, and therefore, there may have been selection against Eurasian mtDNA after its initial introduction into the population.

American Journal of Physical Anthropology

Early View (Articles online in advance of print)

Brief communication: mtDNA variation in North Cameroon: Lack of asian lineages and implications for back migration from Asia to sub-Saharan Africa

Valentina Coia et al.


The hypervariable region-1 and four nucleotide positions (10400, 10873, 12308, and 12705) of the coding region of mitochondrial DNA (mtDNA) were analyzed in 441 individuals belonging to eight populations (Daba, Fali, Fulbe, Mandara, Uldeme, Podokwo, Tali, and Tupuri) from North Cameroon and four populations (Bakaka, Bassa, Bamileke, and Ewondo) from South Cameroon. All mtDNAs were assigned to five haplogroups: three sub-Saharan (L1, L2, and L3), one northern African (U6), and one European (U5). Our results contrast with the observed high frequencies of a Y-chromosome haplogroup of probable Asian origin (R1*-M173) in North Cameroon. As a first step toward a better understanding of the evident discrepancy between mtDNA and Y-chromosome data, we propose two contrasting scenarios. The first one, here termed "migration and asymmetric admixture," implies a back migration from Asia to North Cameroon of a population group carrying the haplotype R1*-M173 at high frequency, and an admixture process restricted to migrant males. The second scenario, on the other hand, temed "divergent drift," implies that modern populations of North Cameroon originated from a small population group which migrated from Asia to Africa and in which, through genetic drift, Y-chromosome haplotype R1*-M173 became predominant, whereas the Asian mtDNA haplogroups were lost.


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