Genetic admixture estimates byAluelements in Afro-Colombian and Mestizo populations from Antioquia, Colombia

Admixture and genetic diversity distribution patterns of non-recombining lineages of Native American ancestry in Colombian populations

Genetic diversity of present American populations results from very complex demographic events involving different types and degrees of admixture. Through the analysis of lineage markers such as mtDNA and Y chromosome it is possible to recover the original Native American haplotypes, which remained identical since the admixture events due to the absence of recombination. However, the decrease in the effective population sizes and the consequent genetic drift effects suffered by these populations during the European colonization resulted in the loss or under-representation of a substantial fraction of the Native American lineages. In this study, we aim to clarify how the diversity and distribution of uniparental lineages vary with the different demographic characteristics (size, degree of isolation) and the different levels of admixture of extant Native groups in Colombia. We present new data resulting from the analyses of mtDNA whole control region, Y chromosome SNP haplogroups and STR haplotypes, and autosomal ancestry informative insertion-deletion polymorphisms in Colombian individuals from different ethnic and linguistic groups. The results demonstrate that populations presenting a high proportion of non-Native American ancestry have preserved nevertheless a substantial diversity of Native American lineages, for both mtDNA and Y chromosome. We suggest that, by maintaining the effective population sizes high, admixture allowed for a decrease in the effects of genetic drift due to Native population size reduction and thus resulting in an effective preservation of the Native American non-recombining lineages.

African genetic ancestry is associated with a protective effect on Dengue severity in colombian populations

The wide variation in severity displayed during Dengue Virus (DENV) infection may be influenced by host susceptibility. In several epidemiological approaches, differences in disease outcomes have been found between some ethnic groups, suggesting that human genetic background has an important role in disease severity. In the Caribbean, It has been reported that populations of African descent present considerable less frequency of severe forms compared with Mestizo and White self-reported groups. Admixed populations offer advantages for genetic epidemiology studies due to variation and distribution of alleles, such as those involved in disease susceptibility, as well to provide explanations of individual variability in clinical outcomes. The current study analysed three Colombian populations, which like most of Latin American populations, are made up of the product of complex admixture processes between European, Native American and African ancestors; having as a main goal to assess the effect of genetic ancestry, estimated with 30 Ancestry Informative Markers (AIMs), on DENV infection severity. We found that African ancestry has a protective effect against severe outcomes under several systems of clinical classification: Severe Dengue (OR: 0.963 for every 1% increase in African ancestry, 95% confidence interval (0.934-0.993), p-value: 0.016), Dengue Haemorrhagic Fever (OR: 0.969, 95% CI (0.947-0.991), p-value: 0.006), and occurrence of haemorrhages (OR: 0.971, 95% CI (0.952-0.989), p-value: 0.002). Conversely, decrease from 100% to 0% African ancestry significantly increases the chance of severe outcomes: OR is 44-fold for Severe Dengue, 24-fold for Dengue Haemorrhagic Fever, and 20-fold for occurrence of haemorrhages. Furthermore, several warning signs also showed statistically significant association given more evidences in specific stages of DENV infection. These results provide consistent evidence in order to infer statistical models providing a framework for future genetic epidemiology and clinical studies.

Interethnic admixture and the evolution of Latin American populations

A general introduction to the origins and history of Latin American populations is followed by a systematic review of the data from molecular autosomal assessments of the ethnic/continental (European, African, Amerindian) ancestries for 24 Latin American countries or territories. The data surveyed are of varying quality but provide a general picture of the present constitution of these populations. A brief discussion about the applications of these results (admixture mapping) is also provided. Latin American populations can be viewed as natural experiments for the investigation of unique anthropological and epidemiological issues.

Microsatellites and Alu elements from the human MHC in Valencia (Spain): analysis of genetic relationships and linkage disequilibrium

Two different sets of noncoding markers (microsatellites and Alu elements) from the human chromosome six were analysed in 106 individuals from Valencia (Spain), with the aim of exploring the effect of evolutionary forces on the genetic variability of the major histocompatibility complex (MHC) and assessing the potential usefulness of these genetic loci in phylogenetic studies. Linkage disequilibrium (LD) analyses revealed statistically significant associations among markers located in the MHC class I region, and also between the microsatellite D6S2792 and several genetic loci from MHC class I, II and III regions. Results of the Ewens-Watterson test indicated that only D6S2792 showed significant departure from selective neutrality. Despite the paucity of haplotype data in the literature, results of the phylogenetic analyses at world scale (Alu elements) showed that the genetic relationships of Valencia were mainly determined by the ethnic ancestry of the populations considered, whereas at European scale (microsatellites) population affinities were strongly influenced by geography. Our findings suggest that noncoding markers from the MHC such as Alu and microsatellite loci might have a potential value as lineage (ancestry) markers in investigations into evolutionary, medical and forensic perspectives.

Microevolutionary processes due to landscape features in the province of Jujuy (Argentina)

OBJECTIVES

We seek to evaluate the influence of a diverse and rugged physical environment on the genetic background of human populations.

METHODS

We analyzed eight polymorphic Alu insertions in 226 individuals from Jujuy province (Argentina), which is composed of several regions with well-defined geographical features and marked contrasts between them associated with differences in altitude (range: 700-3300 m). This regional division was used to assess the spatial variation of the Alu diversity.

RESULTS

Deviations from Hardy-Weinberg Equilibrium expectations resulting from heterozygous deficit were found for FXIIIB and PV92 in the highest subpopulations. Several Alu elements showed genetic heterogeneity between the highest region (La Puna) and the lowest regions (Valle and Selva). Similarly, a decreasing trend of the average heterozygosity according to altitude was found. Both the centroid method and the admixture analysis unveiled a gene flow above the average in lowland populations, indicating a higher proportion of foreign genes introduced by immigrants of European and African ancestry. Furthermore, several Alu frequency clines fitting the orientation of the altitude gradient were detected.

CONCLUSIONS

Our study reveals a spatial patterning of the Alu diversity in Jujuy, most likely determined by disparities in landscape and environmental features between the different subregions. Differences in the physical environment would have drastically reduced the homogenizing effects of the gene flow and would have promoted genetic drift episodes in the highest subpopulations. Microevolutionary processes detected in Jujuy have played an important role in the shaping of the gene pool of the populations from this sub-Andean zone from Argentina.