scholarly journals A Scan for Signatures of Positive Selection in Candidate Loci for Skin Pigmentation in Humans

2006 ◽  
Vol 23 (9) ◽  
pp. 1697-1706 ◽  
Author(s):  
Neskuts Izagirre ◽  
Iker García ◽  
Corina Junquera ◽  
Concepción de la Rúa ◽  
Santos Alonso
Keyword(s):  
Positive Selection ◽  
Skin Pigmentation ◽  
Candidate Loci

scholarly journals Identifying positive selection candidate loci for high-altitude adaptation in Andean populations

2009 ◽  
Vol 4 (2) ◽  
Author(s):  
Abigail W. Bigham ◽  
Xianyun Mao ◽  
Rui Mei ◽  
Tom Brutsaert ◽  
Megan J. Wilson ◽  
...  
Keyword(s):  
Positive Selection ◽  
High Altitude ◽  
Selection Candidate ◽  
High Altitude Adaptation ◽  
Altitude Adaptation ◽  
Candidate Loci

scholarly journals Recent population genomic insights into the genetic basis of arsenic tolerance in humans: the difficulties of identifying positively selected loci in strongly bottlenecked populations

Heredity ◽  
2019 ◽  
Vol 124 (2) ◽  
pp. 253-262 ◽  
Author(s):  
Mario Apata ◽  
Susanne P. Pfeifer
Keyword(s):  
Genetic Basis ◽  
Demographic History ◽  
Skin Pigmentation ◽  
Modern Human ◽  
Human Populations ◽  
Population Bottlenecks ◽  
Arsenic Tolerance ◽  
Local Adaptations ◽  
Population Genomic ◽  
Candidate Loci

AbstractRecent advances in genomics have enabled researchers to shed light on the evolutionary processes driving human adaptation, by revealing the genetic architectures underlying traits ranging from lactase persistence, to skin pigmentation, to hypoxic response, to arsenic tolerance. Complicating the identification of targets of positive selection in modern human populations is their complex demographic history, characterized by population bottlenecks and expansions, population structure, migration, and admixture. In particular, founder effects and recent strong population size reductions, such as those experienced by the indigenous peoples of the Americas, have severe impacts on genetic variation that can lead to the accumulation of large allele frequency differences between populations due to genetic drift rather than natural selection. While distinguishing the effects of demographic history from selection remains challenging, neglecting neutral processes can lead to the incorrect identification of candidate loci. We here review the recent population genomic insights into the genetic basis of arsenic tolerance in Andean populations, and utilize this example to highlight both the difficulties pertaining to the identification of local adaptations in strongly bottlenecked populations, as well as the importance of controlling for demographic history in selection scans.

scholarly journals Positive selection in admixed populations from Ethiopia

BMC Genetics ◽  
2020 ◽  
Vol 21 (S1) ◽  
Author(s):  
Sandra Walsh ◽  
Luca Pagani ◽  
Yali Xue ◽  
Hafid Laayouni ◽  
Chris Tyler-Smith ◽  
...  
Keyword(s):  
Positive Selection ◽  
T Cell Receptors ◽  
Skin Pigmentation ◽  
Main Role ◽  
Functional Categories ◽  
Adaptive Selection ◽  
Wide Range ◽  
African Populations ◽  
Polygenic Adaptation

Abstract Background In the process of adaptation of humans to their environment, positive or adaptive selection has played a main role. Positive selection has, however, been under-studied in African populations, despite their diversity and importance for understanding human history. Results Here, we have used 119 available whole-genome sequences from five Ethiopian populations (Amhara, Oromo, Somali, Wolayta and Gumuz) to investigate the modes and targets of positive selection in this part of the world. The site frequency spectrum-based test SFselect was applied to idfentify a wide range of events of selection (old and recent), and the haplotype-based statistic integrated haplotype score to detect more recent events, in each case with evaluation of the significance of candidate signals by extensive simulations. Additional insights were provided by considering admixture proportions and functional categories of genes. We identified both individual loci that are likely targets of classic sweeps and groups of genes that may have experienced polygenic adaptation. We found population-specific as well as shared signals of selection, with folate metabolism and the related ultraviolet response and skin pigmentation standing out as a shared pathway, perhaps as a response to the high levels of ultraviolet irradiation, and in addition strong signals in genes such as IFNA, MRC1, immunoglobulins and T-cell receptors which contribute to defend against pathogens. Conclusions Signals of positive selection were detected in Ethiopian populations revealing novel adaptations in East Africa, and abundant targets for functional follow-up.

Fine-scale genetic structuring, divergent selection, and conservation prospects for the overexploited crab (Cardisoma guanhumi) in tropical mangroves from North-eastern Brazil

2016 ◽  
Vol 96 (8) ◽  
pp. 1677-1686 ◽  
Author(s):  
D.J. Gama-Maia ◽  
R.A. Torres
Keyword(s):  
Genetic Variation ◽  
Positive Selection ◽  
Conservation Status ◽  
Fine Scale ◽  
Genetic Structuring ◽  
Economic Resource ◽  
Study Region ◽  
Heterogeneous Distribution ◽  
Cardisoma Guanhumi ◽  
Candidate Loci

Popularly known as blue land crab,Cardisoma guanhumiis heavily exploited as food and considered as an important economic resource in Brazil. In recent decades, the species has experienced a sharp population decline by the loss and/or degradation of its natural habitat and overfishing. The present study aimed to investigate the genetic variation and connectivity among 154 specimens ofC. guanhumisampled along the coast of Pernambuco in five different levels of tropical mangroves conservation. Nine ISSR primers were used for assessing the genetic variation of the species. The genetic diversity observed inC. guanhumiwas high reinforcing the condition of a resilient species, indicating a good conservation status of this resource in Pernambuco. The hypothesis of panmixia was rejected in favour of a heterogeneous distribution of the genotypes ofC. guanhumi(ФST= 0.19) despite the high gene flow observed in the study region. Such difference could be attributed to the candidate loci being under positive selection and differentially distributed between the geographic regions assessed. The genetic structure showed a pattern of fine-scale genetic structuring better fitted to a model of selection-mediated geographic cline. Cluster analysis and candidate loci under positive selection suggested that the populations ofC. guanhumiin the North-central and South coasts of Pernambuco might be different management units and must be managed independently. In conclusion, exhaustion of natural stocks upon which fishing is totally dependent will lead to serious ecological and sociocultural impacts.

Ultrastructure of melanocyte-keratinocyte interactions and pigment transfer in vitro

1978 ◽  
Vol 36 (2) ◽  
pp. 650-651
Author(s):  
Raul I. Garcia ◽  
Evelyn A. Flynn ◽  
George Szabo
Keyword(s):  
Direct Injection ◽  
Skin Pigmentation ◽  
Freeze Fracture ◽  
Pigment Granule ◽  
Time Lapse ◽  
Ultrastructural Level ◽  
Lanthanum Tracer ◽  
A Cell

Skin pigmentation in mammals involves the interaction of epidermal melanocytes and keratinocytes in the structural and functional unit known as the Epidermal Melanin Unit. Melanocytes(M) synthesize melanin within specialized membrane-bound organelles, the melanosome or pigment granule. These are subsequently transferred by way of M dendrites to keratinocytes(K) by a mechanism still to be clearly defined. Three different, though not necessarily mutually exclusive, mechanisms of melanosome transfer have been proposed: cytophagocytosis by K of M dendrite tips containing melanosomes, direct injection of melanosomes into the K cytoplasm through a cell-to-cell pore or communicating channel formed by localized fusion of M and K cell membranes, release of melanosomes into the extracellular space(ECS) by exocytosis followed by K uptake using conventional phagocytosis. Variability in methods of transfer has been noted both in vivo and in vitro and there is evidence in support of each transfer mechanism. We Have previously studied M-K interactions in vitro using time-lapse cinemicrography and in vivo at the ultrastructural level using lanthanum tracer and freeze-fracture.

Alterations during Positive Selection in the Thymus of nackt CD4-Deficient Mice

2000 ◽  
Vol 52 (6) ◽  
pp. 555-562 ◽  
Author(s):  
I. Nepomnaschy ◽  
G. Lombardi ◽  
P. Bekinschtein ◽  
P. Berguer ◽  
V. Francisco ◽  
...  
Keyword(s):  
Positive Selection ◽  
Deficient Mice

Skin pigmentation and chlorpromazine

JAMA ◽  
1965 ◽  
Vol 194 (6) ◽  
pp. 670-672 ◽  
Author(s):  
A. S. Zelickson
Keyword(s):  
Skin Pigmentation
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