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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 (Rl*-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. KEY WORDS mtDNA U6 haplogroup; Y-chromosome R1*-M173 haplogroup; Fulbe

Combined use of biallelic and microsatellite Y-chromosome polymorphisms in finding affinities among African populations is discussed. Seven biallelic polymorphic sites were studied to define Y-chromosome haplotypes. Data was combined with those from four dinucleotide-repeat polymorphisms. The object was to establish Y-chromosome compound superhaplotypes. Geographic closeness seems better as a predictor of genetic affinity than language and genetic similarities.

An analysis based on two systems for describing the human mitochondrial genome (mtDNA) has been carried out using 95 samples from the Near East and northwest Caucasus. One procedure is assaying restriction fragment length polymorphisms (RFLPs) all through the genome and the other is sequencing of parts of the control region (CR). The concordance of the two systems has been demonstrated. Variation in mtDNA is used to infer histories of peoples. The most refined phylogeny so far found for west Eurasian mtDNA has been presented and a nomenclature described and applied for mtDNA clusters. Hypervariable nucleotides have been identified. Relative mutation rates of the two systems have been evaluated with ambiguities identified. Berber speakers were sampled and a identification of signature mutations for each cluster led to a hierarchical scheme for finding cluster composition. The main indigenous North African cluster is a sister group to the most ancient cluster of European mRNAs. It diverged about 50,000 years ago.

A possible ancient link between Europe/Western Asia and North America in mtDNA haplogroup X is discussed with information on investigation of the origins, continental relationships and diversity of the haplogroup. Investigation was carried out with mtDNA high-resolution RFLP and complete control region sequence analysis of 14 putative European haplogroup X and 22 putative Native American haplogroup X mtDNAs and identified a consensus haplogroup X motif characterizing Native American and European samples, so some Native American founders may have had Caucasian ancestry.

Common descent followed by molecular radiation accounts for most of the phenetic relationships among haplotypes in four Y-linked dinucleotide microsatellites among 908 men from Europe, northern Africa, and western Asia. Six large networks and two small ones emerged. The complete diversity within a sample can be partitioned using this technique. A low level of homoplasy is found among dinucleotide microsatellite haplotypes. Populations are highly structured in terms of Y-chromosomal network frequencies.

In two population samples of 77 Bamileke (Bantu sensu lato) and 18 Bakaka (Bantu sensu stricto) from southwestern Cameroon, the mtDNA RFLPs for the HpaI, HaeII, MspI, AvaII, and HincII enzymes were studied. Two of the MspI morphs had not been reported before. Six new types were found, four of which represent new combinations of previously described morphs. The AvaII morph 3 was found in association with the 'African' HpaI morph 3. This finding is in line with previous observations in Negroids and demonstrates the usefulness of this combination as an indicator of black African ancestry. Two differences were noted between the groups: a lower frequency of HpaI morph 3 and a higher frequency of HaeII morph 4 in the Bakaka with respect to the Bamileke (0.44 versus 0.62 and O.17 versus 0.03, respectively). The importance of these differences could not be evaluated because the Bakaka sample was too small. Nevertheless, because the Bamileke show a relatively low frequency of mtDNA type 1 (2.1.1.1.1.-) and high frequencies of mtDNA types 2 (3.1.1.1.3.-) and 7 (3.1.1.1.1.-), they can be placed with the other Negroids so far examined, but they are closer to the Senegalese than to the Bantu from South Africa. In comparing the Bamileke and the Bantu, mtDNA type 3 (3.1.1.2.2.-) appears particularly discriminative because it is present in all the Bantu subgroups examined but not in the Bamileke. mtDNA type 39 (2.1.4.1.1.-), which was observed only in the Bamileke, might be considered likewise discriminative, although to a lesser degree., The central-western African region of Cameroon has been an area of great interest for anthropological and linguistic studies. Its long and complicated history of peopling has led to considerable ethnic [...]

The azoospermia factor c region (AZFc), located in the long arm of the human Y chromosome, is frequently involved in chromosome rearrangements, mainly due to non-allelic homologous recombination events that occur between the nearly identical sequences (amplicon) that comprises it. These rearrangements may have major phenotypic effects like spermatogenic failure or other pathologies linked to male infertility. Moreover, they may also be relevant in forensic genetics, since some of the Y chromosome short tandem repeats (Y-STRs) commonly used in forensic analysis are located in amplicons or in inter-amplicon sequences of the AZFc. In a previous study, we identified four phylogenetically related samples with a null allele at DYS448 and a tetrallelic pattern at DYF387S1, two Y-STRs located in the AZFc. Through NGS read depth analysis, we found that the unusual Y-STR pattern may be due to a 1.6 Mb deletion arising concurrently or after a 3.5 Mb duplication event. The observed large genomic rearrangement results in copy number reduction for the RBMY gene family as well as duplication of other AZFc genes. Based on the diversity of 16 additional Y-STRs, we estimated that the duplication/deletion event occurred at least twenty generations ago, suggesting that it has not been affected by negative selection. [ABSTRACT FROM AUTHOR]

The Dominican Republic is one of the two countries on the Hispaniola island, which is part of the Antilles. Hispaniola was affected by the European colonization and massive deportation of African slaves since the XVI century and these events heavily shaped the genetic composition of the present-day population. To shed light about the effect of the European rules, we analyzed 92 single nucleotide polymorphisms on the Y chromosome in 182 Dominican individuals from three different locations. The Dominican Y haplogroup composition was characterized by an excess of northern African/European lineages (59%), followed by the African clades (38%), whereas the Native-American lineages were rare (3%). The comparison with the mitochondrial DNA variability, dominated by African clades, revealed a sex-biased admixture pattern, in line with the colonial society dominated by European men. When other Caribbean and non-Caribbean former colonies were also considered, we noted a difference between territories under a Spanish rule (like the Dominican Republic) and British/French rule, with the former characterized by an excess of European Y lineages reflecting the more permissive Iberian legislation about mixed people and slavery. Finally, we analyzed the distribution in Africa of the Dominican lineages with a putative African origin, mainly focusing on central and western Africa, which were the main sources of African slaves. We found that most (83%) of the African lineages observed in Santo Domingo have a central African ancestry, suggesting that most of the slaves were deported from regions. [ABSTRACT FROM AUTHOR]

The male-specific region of the human Y chromosome (MSY) is characterized by the lack of meiotic recombination and it has long been considered an evolutionary independent region of the human genome. In recent years, however, the idea that human MSY did not have an independent evolutionary history begun to emerge with the discovery that inter-chromosomal gene conversion (ICGC) can modulate the genetic diversity of some portions of this genomic region. Despite the study of the dynamics of this molecular mechanism in humans is still in its infancy, some peculiar features and consequences of it can be summarized. The main effect of ICGC is to increase the allelic diversity of MSY by generating a significant excess of clustered single nucleotide polymorphisms (SNPs) (defined as groups of two or more SNPs occurring in close proximity and on the same branch of the Y phylogeny). On the human MSY, 13 inter-chromosomal gene conversion hotspots (GCHs) have been identified so far, involving donor sequences mainly from the X-chromosome and, to a lesser extent, from autosomes. Most of the GCHs are evolutionary conserved and overlap with regions involved in aberrant X-Y crossing-over. This review mainly focuses on the dynamics and the current knowledge concerning the recombinational landscape of the human MSY in the form of ICGC, on how this molecular mechanism may influence the evolution of the MSY, and on how it could affect the information enclosed within a genomic region which, until recently, appeared to be an evolutionary independent unit. [ABSTRACT FROM AUTHOR]

Factors affecting the rate and pattern of the mutational process are being identified for human autosomes, but the same relationships for the male specific portion of the Y chromosome (MSY) are not established. We considered 3,390 mutations occurring in 19 sequence bins identified by sequencing 1.5 Mb of the MSY from each of 104 present-day chromosomes. The occurrence of mutations was not proportional to the amount of sequenced bases in each bin, with a 2-fold variation. The regression of the number of mutations per unit sequence against a number of indicators of the genomic features of each bin, revealed the same fundamental patterns as in the autosomes. By considering the sequences of the same region from two precisely dated ancient specimens, we obtained a calibrated region-specific substitution rate of 0.716 × 10-9/site/year. Despite its lack of recombination and other peculiar features, the MSY then resembles the autosomes in displaying a marked regional heterogeneity of the mutation rate. An immediate implication is that a given figure for the substitution rate only makes sense if bound to a specific DNA region. By strictly applying this principle we obtained an unbiased estimate of the antiquity of lineages relevant to the genetic history of the human Y chromosome. In particular, the two deepest nodes of the tree highlight the survival, in Central-Western Africa, of lineages whose coalescence (291 ky, 95% C.I. 253–343) predates the emergence of anatomically modern features in the fossil record. [ABSTRACT FROM AUTHOR]