Y-chromosome polymorphisms and the origins of the European gene pool

Gradients of allele frequencies have long been considered the main genetic characteristic of the European population, but mitochondrial DNA diversity seems to be distributed differently. One Alu insertion (YAP), five tetranucleotide (DYS19, DYS389B, DYS390, DYS391 and DYS393) and one trinucleotide (DYS392) microsatellite loci of the Y chromosome were analysed for geographical patterns in 59 European populations. Spatial correlograms showed clines for most markers, which paralleled the gradients previously observed for two RFLP polymorphisms. Effective separation times between populations were estimated from genetic distances at microsatellite loci. Even after correcting for the possible effects of continuous local gene flow, the most distant Indo-European-speaking populations seem to have separated no more than 7000 years ago. The clinal patterns and the estimated, recent separation times between populations jointly suggest that Y-chromosome diversity in Europe largely reflects a directional demic expansion, which is unlikely to have occurred before the Neolithic period.     

The Geographic Distribution of Human Y Chromosome Variation

We examined variation on the nonrecombining portion of the human Y chromosome to investigate human evolution during the last 200,000 years. The Y-specific polymorphic sites included the Y Alu insertional polymorphism or ``YAP' element (DYS287), the poly(A) tail associated with the YAP element, three point mutations in close association with the YAP insertion site, an A-G polymorphic transition (DYS271), and a tetranucleotide microsatellite (DYS19). Global variation at the five bi-allelic sites (DYS271, DYS287, and the three point mutations) gave rise to five ``YAP haplotypes' in 60 populations from Africa, Europe, Asia, Australasia, and the New World (n = 1500). Combining the multi-allelic variation at the microsatellite loci (poly(A) tail and DYS19) with the YAP haplotypes resulted in a total of 27 ``combination haplotypes'. All five of the YAP haplotypes and 21 of the 27 combination haplotypes were found in African populations, which had greater haplotype diversity than did populations from other geographical locations. Only subsets of the five YAP haplotypes were found outside of Africa. Patterns of observed variation were compatible with a variety of hypotheses, including multiple human migrations and range expansions.     

African and Levantine origins of Pakistani YAP+ Y chromosomes.

We surveyed 9 Pakistani subpopulations for variation on the nonrecombining portion of the Y chromosome. The polymorphic systems examined were the Y-chromosome Alu insertion polymorphism (YAP) at DYS287, 5 single nucleotide polymorphisms, and the tetranucleotide microsatellite DYS19. Y chromosomes carrying the YAP element (YAP+) were found in populations from southwestern Pakistan at frequencies ranging from 2% to 8%, whereas northeastern populations appeared to lack YAP+ chromosomes. In contrast to other South Asian populations, several Pakistani subpopulations had a high frequency of the DYS19*B allele, the most frequent allele in West Asian, North African, and European populations. The combination of alleles at all polymorphic sites gave rise to 9 YAP-DYS19 combination haplotypes in Pakistani populations, including YAP+ haplotypes 4-A, 4-B, 5-C, and 5-E. We hypothesize that the geographic distributions of YAP+ haplotypes 4 and 5 trace separate migratory routes to Pakistan: YAP+ haplotype 5 may have entered Pakistan from the Arabian Peninsula by means of migrations across the Gulf of Oman, whereas males possessing YAP+ haplotype 4 may have traveled over land from the Middle East. These inferences are consistent with ethnohistorical data suggesting that Pakistan's ethnic groups have been influenced by migrations from both African and Levantine source populations.     

Y chromosomal DNA variation and the peopling of Japan.

Four loci mapping to the nonrecombining portion of the Y chromosome were genotyped in Japanese populations from Okinawa, the southernmost island of Japan; Shizuoka and Aomori on the main island of Honshu; and a small sample of Taiwanese. The Y Alu polymorphic (YAP) element is present in 42% of the Japanese and absent in the Taiwanese, confirming the irregular distribution of this polymorphism in Asia. Data from the four loci were used to determine genetic distances among populations, construct Y chromosome haplotypes, and estimate the degree of genetic diversity in each population and on different Y chromosome haplotypes. Evolutionary analysis of Y haplotypes suggests that polymorphisms at the YAP (DYS287) and DXYS5Y loci originated a single time, whereas restriction patterns at the DYS1 locus and microsatellite alleles at the DYS19 locus arose more than once. Genetic distance analysis indicated that the Okinawans are differentiated from Japanese living on Honshu. The data support the hypotheses that modern Japanese populations have resulted from distinctive genetic contributions involving the ancient Jomon people and Yayoi immigrants from Korea or mainland China, with Okinawans experiencing the least amount of admixture with the Yayoi. It is suggested that YAP+ chromosomes migrated to Japan with the Jomon people > 10,000 years ago and that a large infusion of YAP- chromosomes entered Japan with the Yayoi migration starting 2,300 years ago. Different degrees of genetic diversity carried by these two ancient chromosomal lineages may be explained by the different life-styles (hunter-gatherer versus agriculturalist). of the migrant groups, the size of the founding populations, and the antiquities of the founding events.     

Genetic structure of Mediterranean populations revealed by Y-chromosome haplotype analysis

The allelic variability at six Y-chromosome-specific polymorphisms (YAP, DYS19, DYS389-I, DYS390, DYS391, and DYS392) was used to generate male-specific haplotypes in 333 males representing 12 population samples from the region around the Mediterranean sea. Extreme interindividual variation was observed, as more than 160 distinct Y-chromosome variants could be defined as six-locus haplotypes. Concomitant with this high variability, low levels of population genetic structure were observed. In particular, a "core" of populations directly facing the north and the east of the Mediterranean basin, from the Middle East to the Italian Peninsula, was found to be genetically undifferentiated. This observation, supported by a reanalysis of Y-specific binary polymorphisms in the same populations, suggests that at least part of the male-specific gene pools of these populations has either a very recent common origin (that could be related with the Neolithic demic diffusion hypothesis), and/or that gene flow has played a significant role in shaping the patterns of genetic variability in this region. In agreement with both hypotheses, we found that the spatial distribution of DYS392 alleles revealed a marked differentiation between the East and the West of the Mediterranean area. Through the analysis of microsatellite variation, the time to the most recent common ancestor (TMRCA) of the YAP(+) sublineage 4 has been estimated. The estimations, based on two different data sets, turn out to be quite recent (7,000-11,000 YBP), suggesting that this lineage may have been first introduced into Southern Europe through Neolithic migrations from the Middle East.     

Genetic differentiation in South Amerindians is related to environmental and cultural diversity: evidence from the Y chromosome

The geographic structure of Y-chromosome variability has been analyzed in native populations of South America, through use of the high-frequency Native American haplogroup defined by the DYS199-T allele and six Y-chromosome-linked microsatellites (DYS19, DYS389A, DYS389B, DYS390, DYS391, and DYS393), analyzed in 236 individuals. The following pattern of within- and among-population variability emerges from the analysis of microsatellite data: (1) the Andean populations exhibit significantly higher levels of within-population variability than do the eastern populations of South America; (2) the spatial-autocorrelation analysis suggests a significant geographic structure of Y-chromosome genetic variability in South America, although a typical evolutionary pattern could not be categorically identified; and (3) genetic-distance analyses and the analysis of molecular variance suggest greater homogeneity between Andean populations than between non-Andean ones. On the basis of these results, we propose a model for the evolution of the male lineages of South Amerindians that involves differential patterns of genetic drift and gene flow. In the western part of the continent, which is associated with the Andean area, populations have relatively large effective sizes and gene-flow levels among them, which has created a trend toward homogenization of the gene pool. On the other hand, eastern populations-settled in the Amazonian region, the central Brazilian plateau, and the Chaco region-have exhibited higher rates of genetic drift and lower levels of gene flow, with a resulting trend toward genetic differentiation. This model is consistent with the linguistic and cultural diversity of South Amerindians, the environmental heterogeneity of the continent, and the available paleoecological data.     

A study of Y-chromosome microsatellite variation in sub-Saharan Africa: a comparison between F(ST) and R(ST) genetic distances

Seven Y-chromosome microsatellite loci (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, and DYS393) were analyzed in three populations from sub-Saharan Africa: the Bamileke and Ewondo populations from Cameroon and the Hutu from Rwanda. Complete typing was obtained for 112 individuals, and a total of 53 different haplotypes was observed. The single-locus gene diversity, averaged across populations, ranges from 0.100 for the DYS392 locus to 0.610 for the DYS389I locus. The haplotype diversity ranges from 0.832 (Ewondo) to 0.965 (Hutu), with an intermediate value of 0.918 in the Bamileke. The diversity among Bamileke, Ewondo, Hutu, and other sub-Saharan populations selected from the literature was analyzed using both a classical (F(ST)) and a stepwise-based (R(ST)) genetic distance method. The pattern of interpopulational diversity based on F(ST) was congruent with anthropological knowledge, while that based on R(ST) revealed unexpected and unconvincing population affinities. From a practical point of view, our study indicates that Y-chromosome microsatellite data may provide useful information for analyses of interpopulational diversity among sub-Saharan populations if an adequate number of loci and individuals along with an appropriate genetic distance method are used. On a theoretical ground, we propose that the lesser performance of R(ST) compared to F(ST) could be explained by the important role played by genetic drift in shaping the relationships among examined populations.     

The Y-STR genetic diversity of an Idaho Basque population, with comparison to European Basques and US Caucasians

Fifty unrelated Basque males from southwest Idaho were typed for the 17 Y-STR loci in the Yfiler multiplex kit (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, YGATA H4.1 and DYS385a/b). In total, 42 haplotypes were identified, with no more than two individuals sharing a single haplotype. The haplotype diversity (HD) was 0.9935, and gene diversity (D) over loci was 0.457 ± 0.137. The Idaho Basque population was compared to the source population from the Basque autonomous region of Northern Spain and Southern France, as well as a United States Caucasian population. The haplotype diversity for the immigrant Basque sample is within 0.4% of the haplotype diversity of the European Basques (0.9903); thus the power of discrimination is similar for each population. The Idaho Basque population has less diversity in 9 out of 16 loci (considering DYS385a/b together) and 3% less diversity across all loci, compared to the European Basque population. A multidimensional scaling analysis (MDS) was created using pairwise R(ST) values to compare the Idaho Basques to other populations. Based upon R(ST) and F(ST) measures, no significant differentiation was found between the Idaho and source European Basque population.     

Genetic variation of the Y chromosome in Chibcha-speaking Amerindians of Costa Rica and Panama

Genetic variation of the Y chromosome in five Chibchan tribes (Bribri, Cabecar, Guaymi, Huetar, and Teribe) of Costa Rica and Panama was analyzed using six microsatellite loci (DYS19, DYS389A, DYS389B, DYS390, DYS391, and DYS393), the Y-chromosome-specific alphoid system (alphah), the Y-chromosome Alu polymorphism (YAP), and a specific pre-Columbian transition (C-->T) (M3 marker) in the DYS 199 locus that defines the Q-M3 haplogroup. Thirty-nine haplotypes were found, resulting in a haplotype diversity of 0.937. The Huetar were the most diverse tribe, probably because of their high levels of interethnic admixture. A candidate founder Y-chromosome haplotype was identified (15.1% of Chibchan chromosomes), with the following constitution: YAP-, DYS199*T, alphah-II, DYS19*13, DYS389A*17, DYS389B*10, DYS390*24, DYS391*10, and DYS393*13. This haplotype is the same as the one described previously as one of the most frequent founder paternal lineages in native American populations. Analysis of molecular variance indicated that the between-population variation was smaller than the within-population variation, and the comparison with mtDNA restriction data showed no evidence of differential structuring between maternally and paternally inherited genes in the Chibchan populations. The mismatch-distribution approach indicated estimated coalescence times of the Y chromosomes of the Q-M3 haplogroup of 3,113 and 13,243 years before present; for the mtDNA-restriction haplotypes the estimated coalescence time was between 7,452 and 9,834 years before present. These results are compatible with the suggested time for the origin of the Chibchan group based on archeological, linguistic, and genetic evidence.     

中国海南岛三个黎族支系DYS287、DYS19的多态性研究

以中国海南岛（289例）本地黎（97例）、杞黎（96例）和侾黎（96例）人群为研究对象,采用PCR技术及变性聚丙烯酰胺凝胶电泳方法分析了Y染色体特异性微卫星DYS19的等位基因分布规律。本地黎群体检出4种等位基因,杞黎和侾黎群体均检出3种。在3个支系的等位基因中均以194bp的频率为最高,分别是0.711、0.855和0.667。杞黎与侾黎人群DYS19基因座的等位基因频率有极显著差异（P＜0.01）。我们还通过PCR方法调查了3个黎族支系的Alu序列插入基因座DYS287的多态性,结果显示：3个人群均未发生Alu序列插入。     

Polymorphism of the STR-locus of Y chromosomes in Eastern Slavs in three populations from Belorussia, Russia and the Ukraine

Allelic polymorphism of five microsatellite loci of the human Y chromosome (DYS19, DYS390, DYS391, DYS392, and DYS393) was analyzed in samples of male populations from Ukraine, Russia, and Belarus (152 subjects in total). The allelic diversity indices (Dg) were determined for all loci; they varied from 0.23 to 0.72. The mean values of this parameter in the Ukrainian, Russian, and Belarussian populations were 0.45, 0.47, and 0.52, respectively. A total of 53 different haplotypes were found in 152 subjects from three populations. The most frequent haplotype was found in 14.5% of the subjects, whereas 35 haplotypes (23%) were each found in only one person. The haplotypic diversity index (Dhp) was 0.94. The genetic distances between the populations studied and some populations of Western and Central Europe were estimated. These data were used to construct a phylogram (tree) of genetic similarity between the populations, which demonstrated that the three Eastern Slavic populations are genetically close to one another and remote from Western European populations.     

Origin of Amerindian Y-chromosomes as inferred by the analysis of six polymorphic markers

We analysed the frequency of six Y-specific polymorphisms in 105 Amerindian males from seven different populations, 42 Caucasian males, and a small number of males of African, Chinese, and Melanesian origin. The combination of three of the six polymorphisms studied produced four different Y-haplogroups. The haplogroup A (non-variant) was the most frequent one. Eighty-five percent of Amerindians showing haplogroup A have the alphoid II (αhII) and the DYS19A Y-specific markers, an association that is found only in 10% of Caucasians and that has not been detected in Asiatics and Africans. Haplogroups C (YAP+) and D (YAP+ plus an A → G transition in the locus DYS271) are of African origin. Four percent of Amerindians and ∼12% of Caucasians showed haplogroup C; ∼1% of Amerindians and ∼2% of Caucasians had haplogroup D. Haplogroup B is characterized by a C → T transition in nucleotide position 373 of the SRY gene domain; this haplogroup is found in Caucasians (∼12%) and Amerindians (∼4%). None of the Amerindians exhibiting the haplogroups B, C, or D show the haplotype αhII/DYS19A. By haplotyping the Alu insert and the DNA region surrounding the insert in YAP+ individuals, we could demonstrate that Amerindian Y chromosomes bearing African markers (haplogroups C and D) are due to recent genetic admixture. Most non-αhII/DYSl9A Amerindian Y-chromosomes in haplogroup A and most cases in haplogroup B are also due to gene flow. We show that haplotype αhII/DYS19A is in linkage disequilibrium with a C → T transition in the locus DYS199. Our results suggest that most Amerindian Y-chromosomes derive from a single paternal lineage characterized by the αhII/DYS19A/DYS199T Amerindian-specific haplotype. The analysis of a larger sample of native American Y-chromosomes will be required in order to confirm or correct this hypothesis. Am J Phys Anthropol 102:79–89, 1997. © 1997 Wiley-Liss, Inc.     

Biodemographic and molecular analysis of an isolated Alpine population (Postua)

Isolated populations have been the object of several genetic and anthropological studies, since endogamy and inbreeding often lead to the acquisition of a particular gene pool. In this context, we studied the small, ancient population of Postua in the north-western Italian Alps. We used biodemographic and molecular techniques to analyse the population structure in order to evaluate the relationship between geographical and genetic isolation. We examined about 26,000 certificates kept in the town and parish archives, concerning the period from 1640 to 1999. High rates of endogamy and isonymy, short marriage distances and a low ratio between the number of surnames and the number of individuals were inferred. In the molecular analysis, we compared the distribution of Y chromosome SNPs (single nucleotide polymorphisms) with those of mitochondrial variations and Y chromosomal microsatellites (short tandem repeat polymorphisms) in 102 healthy individuals originating from Postua. A control sample (94 individuals) was collected from a plain area, 50 km away. We examined 23 SNPs and an Alu repeat, located in the nonrecombinant portion of the Y chromosome. To further delineate Y chromosome lineages, the biallelic haplogroups were further resolved using Y microsatellite markers (DYS19, DYS391, DYS392, DYS393). Mitochondrial HVS-I and HVS-II regions were sequenced, and RFLP screening with the six classical enzymes was performed. Postua is similar to other populations living in northern Italy, but it shows a lower number of haplotypes. The samples were compared with other European populations. We calculated genetic distances according to Reynold and Nei and we carried out a phylogenetic analysis by phylogenetic trees and reduced median networks construction. Postua clusters with other samples from northern Italy but in a separate position, probably indicating drift phenomena. These relationships are supported by AMOVA (analysis of molecular variance). Our results suggest that the influence of neighbouring populations on the gene pool of Postua has been very low through both females and males.     

Polymorphism of Y-chromosomal microsatellites in Russian populations from the northern and southern Russia as exemplified by the populations of Kursk and Arkhangel'sk Oblast

Allelic polymorphisms at five Y-chromosomal microsatellite loci (DYS19, DYS390, DYS391, DYS392, and DYS393) were typed in 87 individuals from male population samples from two geographically isolated regions (Arkhangelsk oblast and Kursk oblast) of the European part of Russia. The populations examined demonstrated substantial differences in the distribution of the DYS392 (P = 0.005) and DYS393 (P = 0.003) alleles. Estimates of genetic relationships between these populations and some other European populations (including Eastern-Slavic) showed that irrespectively of the measure of genetic distance chosen, Arkhangelsk population was closer to the populations belonging to the Finno-Ugric linguistic group (Saami and Estonians) and to the Estonian geographical neighbors, Latvians, while Kursk population was the member of a cluster formed by Eastern-Slavic populations (Russians of Novgorod oblast, Ukrainians, and Belarussians). Phylogenetic analysis of the most frequent haplotypes indicated that these differences between Kursk and Arkhangelsk populations were associated with high prevalence in the latter of major haplotypes characteristic primarily of the Finno-Ugric populations.     

Polymorphism of STR Loci of the Y Chromosome in Three Populations of Eastern Slavs from Belarus,Russia, and Ukraine

Allelic polymorphism of five microsatellite loci of the human Y chromosome (DYS19, DYS390, DYS391, DYS392, and DYS393) was analyzed in samples of male populations from Ukraine, Russia, and Belarus (152 subjects in total). The allelic diversity indices (D _g) were determined for all loci; they varied from 0.23 to 0.72. The mean values of this parameter in the Ukrainian, Russian, and Belarussian populations were 0.45, 0.47, and 0.52, respectively. A total of 53 different haplotypes were found in 152 subjects from three populations. The most frequent haplotype was found in 14.5% of the subjects, whereas 35 haplotypes (23%) were each found in only one person. The haplotypic diversity index (D _hp) was 0.94. The genetic distances between the populations studied and some populations of Western and Central Europe were estimated. These data were used to construct a phylogram (tree) of genetic similarity between the populations, which demonstrated that the three Eastern Slavic populations are genetically close to one another and remote from Western European populations.     

Regional differences among the Finns: a Y-chromosomal perspective

Twenty-two Y-chromosomal markers, consisting of fourteen biallelic markers (YAP/DYS287, M170, M253, P37, M223, 12f2, M9, P43, Tat, 92R7, P36, SRY-1532, M17, P25) and eight STRs (DYS19, DYS385a/b, DYS388, DYS389I/II, DYS390, DYS391, DYS392, DYS393), were analyzed in 536 unrelated Finnish males from eastern and western subpopulations of Finland. The aim of the study was to analyze regional differences in genetic variation within the country, and to analyze the population history of the Finns. Our results gave further support to the existence of a sharp genetic border between eastern and western Finns so far observed exclusively in Y-chromosomal variation. Both biallelic haplogroup and STR haplotype networks showed bifurcated structures, and similar clustering was evident in haplogroup and haplotype frequencies and genetic distances. These results suggest that the western and eastern parts of the country have been subject to partly different population histories, which is also supported by earlier archaeological, historical and genetic data. It seems probable that early migrations from Finno-Ugric sources affected the whole country, whereas subsequent migrations from Scandinavia had an impact mainly on the western parts of the country. The contacts between Finland and neighboring Finno-Ugric, Scandinavian and Baltic regions are evident. However, there is no support for recent migrations from Siberia and Central Europe. Our results emphasize the importance of incorporating Y-chromosomal data to reveal the population substructure which is often left undetected in mitochondrial DNA variation. Early assumptions of the homogeneity of the isolated Finnish population have now proven to be false, which may also have implications for future association studies.     

Geographic differences in the allele frequencies of the human Y-linked tetranucleotide polymorphism DYS19

We have studied the allele frequency distribution of the microsatellite locus DYS 19 in several populations with different geographical origins worldwide. Three new alleles were found. In addition, remarkable geographic and ethnic differences were observed in the allele frequency profiles and DNA marker (gene) diversity among populations and major ethnic groups. Amerindians showed an overwhelming predominance of the A allele, while in Caucasians the B allele was modal, and in Greater Asians and Africans allele C became predominant. Even within these geographic regions there were significant gradients, as exemplified by the decreasing frequency profile of the B allele from Great Britain over Germany to Slovakia. Thus, DYS 19 emerges as a useful tool for studying the structure and dynamics of human populations.     

Polymorphism of microsatellite loci DYS19, DYS393, and frequency of the T-C transition of the RBF5 locus on the Y-chromosome in inhabitants of the Volga-Ural region

Polymorphism of the DYS19 and DYS393 microsatellite loci and T-C transition at the RBF5 locus of the Y chromosome were analyzed in Volga-Ural populations of Bashkirs, Tatars, Chuvashes, Maris, Mordovians, Udmurts, and Komis. For the DYS19 locus, statistically significant differences were observed between Trans-Ural and Northeastern Bashkirs; between Trans-Ural Bashkirs and Tatars; and between Udmurts and other populations of the Volga-Ural region, excluding Trans-Ural Bashkirs. The DYS393 locus allele frequency distribution patterns were similar in all populations studied. The highest and the lowest frequencies of T-C transition at the RBF5 locus was detected in Udmurts (0.68) and in Mordovians (0.09), respectively. Association of C-alleles with the DYS19/DYS393 microsatellite haplotypes was investigated. The major haplotypes specific to the Turkic- and Finno-Ugric populations were revealed.     

Analysis of five y-Specific microsatellite loci in Asian and Pacific populations

We have analyzed five Y-specific microsatellite loci (DYS388, DYS390, DYS391, DYS394, DYS395) in 17 Asian and Pacific populations representing a broad geographical area and different linguistic families, with an emphasis on populations from mainland and insular Southeast Asia. Analysis of gene diversity indicates that several of the studied populations have experienced substantial genetic isolation, and a reduction in male effective sizes (viz. the Northeast Indian populations Nishi, Adi and the Taiwanese aboriginals). The average values of the F_ST and (_ST statistics indicate a high degree of genetic differentiation among these populations at the five Y-specific markers (F_ST =0.21 and (_ST = 0.33, based on individual loci; F_ST = 0.09 and (_ST = 0.36, based on haplotypes), which conform to the expectation of a fourfold smaller effective size of the Y-linked loci compared with the autosomal loci. Dendrogram and principal coordinates analysis, with few exceptions, show a major separation between mainland and insular populations. Among the mainland populations, the Tibeto-Burman speakers from Northeast India cluster in a well-defined group, supported by high bootstrap values. The Southern Chinese, Northern Thai, So, and Cambodian also are integral to this cluster. The other major cluster is rather heterogeneous and includes, among others, the Austronesian-speaking populations. The Samoans of the Pacific, with a distinctive pattern of allelic distributions, stand as an outlier in the tree and PC representations. Although trends of genetic affinities among ethnically and geographically related populations are evident from the Y-specific microsatellite data, microsatellites are not optimal for deciphering complex migratory patterns of human populations, which could possibly be clarified by using additional and more stable genetic markers. Am J Phys Anthropol 110: 1–16, 1999. © 1999 Wiley-Liss, Inc.     

Genetic structure of American black bears in the desert southwest of North America: conservation implications for recolonization

American black bears (Ursus americanus) have recolonized parts of their former range in the Trans-Pecos region of western Texas after a >40-year absence. Assessment of genetic variation, structuring, gene flow, and dispersal among bear populations along the borderlands of Mexico and Texas is important to gain a better understanding of recolonization by large carnivores. We evaluated aspects of genetic diversity and gene flow for 6 sampling areas of black bears in southwestern North America using genotypic data from 7 microsatellite loci. Our results indicated that genetic diversity generally was high in the metapopulation of black bears in northern Mexico and western Texas. The episodic gene flow occurring via desert corridors between populations in northern Mexico and those in western Texas has permitted the establishment of only moderate levels of genetic structuring. Bayesian clustering analyses and assignment testing depicted the presence of 3 subpopulations among our 6 sampling areas and attested to the generally panmictic nature of bear populations in the borderlands region. The potentially ephemeral nature of the small populations in western Texas and genotypic characteristics of bears recolonizing these habitats attest to the importance of linkages along this portion of the borderlands of the United States and Mexico to effectively conserve and manage the species in this part of its range.