The population genetic effects of ancestry and admixture in a subdivided cattle breed

The genetic structure of the Dexter, a minority cattle breed with complex demographic history, was investigated using microsatellite markers and a range of statistical approaches designed to detect both admixture and genetic drift. Modern representatives of two putative ancestral populations, the Devon and Kerry, together with the different populations of the Dexter, which have experienced different demographic histories, were analysed. Breed units showed comparatively high levels of genetic variability ( H _E = 0.63–0.68); however, distinct genetic subgroups were detected within the Dexter, which could be attributed to known demographic events. Much lower diversity was identified in three small, isolated Dexter populations ( H _E = 0.52–0.55) and higher differentiation ( F _ST > 0.13) was found. For one of these populations, where strong selection has taken place, we also found evidence of a demographic bottleneck. Three methods for quantifying breed admixture were applied and substantial method-based variation in estimates for the genetic contribution of the two proposed ancestral populations for each subdivision of the Dexter was found. Results were consistent only in the case of a group consisting of selected Traditional Dexter animals, where the ancestor of the modern Kerry breed was also determined as the greater parental contributor to the Dexter. The inconsistency of estimation of admixture proportions between the methods highlights the potentially confounding role of genetic drift in shaping small population structure, and the consequences of accurately describing population histories from contemporary genetic data.     

Ethnicity and Evolution of the Biodemographic Structure of Arbëreshe and Italian Populations of the Pollino Area, southern Italy (1820–1984)

In the present study, we show how, through time, an ethnic mosaic and a changing social and economic context translated into intrapopulation differentiation and a change in genetic barriers between populations. Surname analysis was applied to a sample drawn from two centuries of marriage records in ten Arbëreshe and nine Italian villages of southern Italy to evaluate the evolution of internal differentiation and changes in genetic relationships between populations. Marital Isonymy and subdivision into subpopulations was higher in the Arbëreshe. Genetic barriers coinciding with ethnic boundaries characterized the 1800s. In the second half of the 1900s, ethnic differentiation disappeared. We hypothesize that socioeconomic changes, such as increased outmigration and regional mobility, were the forces that progressively eliminated the ethnic-related genetic differentiation in the region. This study has important implications for an understanding of the relationship between genetic evolution and the cultural milieu involving enforcement of ethnic differences.     

Genetic structure of two urban afro-brazilian populations

A total of 218 individuals living in the Brazilian cities of Porto Alegre (in the South) and Salvador (in the Northeast) were variously studied in relation to nine erythrocyte and four plasma protein systems. The results were compared with previous studies in some of these systems, and estimates of interethnic admixture obtained in subsamples according to morphological appearance. As a whole, Afro-Brazilians from Salvador show 42% of non-African genes, the corresponding figure for Porto Alegre being 59%. The Amerindian contribution to these individuals was estimated as null or negligible. Average heterozygosities are similar to those obtained for African groups, but the gene differentiation coefficient (GST') is small. The phylogenetic tree indicates a closer relationship of Salvador with the African subcluster, as would be expected by the admixture and istorical data. Analyses such as this one are important for the unraveling of the complex networks responsible for the present variability of human populations, and for the dispelling of racist concepts.     

Global human genetics of HIV-1 infection and China

Genetic polymorphisms in human genes can influence the risk for HIV-1 infection and disease progression, although the reported effects of these alleles have been inconsistent. This review highlights the recent discoveries on global and Chinese genetic polymorphisms and their association with HIV-1 transmission and disease progression.     

Genetic characterization of Latin-American Creole cattle using microsatellite markers

Genetic diversity in and relationships among 26 Creole cattle breeds from 10 American countries were assessed using 19 microsatellites. Heterozygosities, F-statistics estimates, genetic distances, multivariate analyses and assignment tests were performed. The levels of within-breed diversity detected in Creole cattle were considerable and higher than those previously reported for European breeds, but similar to those found in other Latin American breeds. Differences among breeds accounted for 8.4% of the total genetic variability. Most breeds clustered separately when the number of pre-defined populations was 21 (the most probable K value), with the exception of some closely related breeds that shared the same cluster and others that were admixed. Despite the high genetic diversity detected, significant inbreeding was also observed within some breeds, and heterozygote excess was detected in others. These results indicate that Creoles represent important reservoirs of cattle genetic diversity and that appropriate conservation measures should be implemented for these native breeds in order to minimize inbreeding and uncontrolled crossbreeding.     

猪CAST基因的单核苷酸多态性及其对肉质性状的效应

CAST基因作为肉质性状的主要候选基因.以80头外来猪和190头地方猪为材料,在CAST基因内含子24上检测到两个多态性位点(A916G 和C1633G ).在916位点上,长白猪和大白猪以A基因为优势基因,其频率分别为0.88和1.00;莱芜猪,大薄莲猪,沂蒙黑猪和里岔黑猪以B基因为优势基因,其频率分别为0.93, 0.97, 0.78和0.68.在1633位点上,长白猪和大白猪以C基因为优势基因,其频率分别为0.82和0.79:莱芜猪,大薄莲猪,沂蒙黑猪和里岔黑猪以D基因为优势基因,其频率分别为1.00, 1.00, 0.88, 0.78.在试验猪种中,共检测到6种单倍型(AACC,AACD,AADD,ABCC,BBCC,BBDD).单倍型分布的多重比较结果表明,外来猪种(长白猪和大白猪)与地方猪种(莱芜猪,大薄莲猪,沂蒙黑猪和里岔黑猪)比较差异极显著(P < 0.01).固定效应模型分析结果表明,嫩度,屠宰45 min后pH值和滴水损失单倍型间差异显著(P < 0.05).最小二乘分析结果表明,外来猪种与地方猪种在嫩度,屠宰45 min后pH值和滴水损失间差异显著(P < 0.05).BBDD单倍型个体与其它单倍型个体比较,嫩度及滴水损失差异显著(P < 0.05);AADD,BBCC,BBDD单倍型个体与其它单倍型个体比较,屠宰45 min后pH值差异显著(P < 0.05).因此,在育种过程中将CAST基因应用于标记辅助选择,将有利于改善猪肉品质,加快育种进程.     

猪MyoG基因内含子1的一个遗传多态性及其遗传效应分析

以长白猪(73),大白猪(68),沂蒙黑猪(57)和莱芜猪(83)为研究对象,采用PCR-SSCP方法 对猪MyoG基因遗传多态性进行分析,并研究基因型与初生重、日增重、肌肉嫩度和背膘厚的相关性.根据猪MyoG 基因的DNA序列（M14331）设计引物,结果在内含子1扩增的片段上发现了一个多态性,检测到2个等位基因(A、B),3种基因型（AA、AB、BB）,并对纯合子进行测序,发现2　943位G→C突变.基因型在不同猪种分布的多重比较,结果表明,大白猪与长白猪、沂蒙黑猪和莱芜猪比较差异显著（P<0.05）,莱芜猪与长白猪和沂蒙黑猪比较差异显著（P<0.05）,长白猪与沂蒙黑猪比较差异不显著（P>0.05）.固定效应模型分析结果表明,初生重及嫩度基因型间差异显著（P<0.01）,而日增重及背膘厚基因型间差异不显著（P>0.05）.最小二乘分析结果表明,BB基因型个体与AA基因型个体比较肌肉嫩度的差异显著（P<0.05）,AA基因型个体与AB和BB基因型个体比较背膘厚的差异显著（P<0.05）.因此,推测MyoG基因对猪肉品质、生长速度及背膘厚存在一定的影响,将 MyoG基因应用于猪育种过程中的标记辅助选择将可以改善猪肉品质,提高生长速度,加快猪的育种进程.     

猪CAST基因的遗传多态性及遗传效应分析

采用PCR—SSCP方法对猪cAST基因遗传多态性进行分析。并研究基因型与肉质性状和背膘厚的相关性。根据猪CAST基因的cDNA序列（M20160）设计7对引物。结果在F1／R1。F6／R6引物对扩增的片段上发现了多态性。并对纯合子进行测序。发现317位A—G突变。2042位G—C突变。基因型在不同猪种分布的多重比较结果表明。长白猪、大白猪和杜洛克猪与沂蒙黑猪和莱芜猪比较差异极显著（P〈0．01）。固定效应模型分析结果表明,嫩度及背膘厚基因型间差异显著（P〈0．05）,而pH值、温度及滴水损失基因型间差异不显著（P〉0．05）。最小二乘分析结果表明,不同猪种比较,屠宰12h和24h后肌肉温度、30min和1h后pH值及滴水损失差异显著（P〈0．05）;BBCC和BBDD单元型个体与其他单元型个体比较肌肉嫩度的差异显著（P〈0．01）。AACC和AADD单元型个体与其他单元型个体比较背膘厚的差异显著（P〈0．01）。因此,推测CAST基因对猪肉品质及背膘厚存在一定的影响。将CAST基因应用于猪育种过程中的标记辅助选择将可以改善猪肉品质。加快猪的育种进程。