Detecting Genetic Isolation in Human Populations: A Study of European Language Minorities

Abstract

The identification of isolation signatures is fundamental to better understand the genetic structure of human populations and to test the relations between cultural factors and genetic variation. However, with current approaches, it is not possible to distinguish between the consequences of long-term isolation and the effects of reduced sample size, selection and differential gene flow. To overcome these limitations, we have integrated the analysis of classical genetic diversity measures with a Bayesian method to estimate gene flow and have carried out simulations based on the coalescent. Combining these approaches, we first tested whether the relatively short history of cultural and geographical isolation of four “linguistic islands” of the Eastern Alps (Lessinia, Sauris, Sappada and Timau) had left detectable signatures in their genetic structure. We then compared our findings to previous studies of European population isolates. Finally, we explored the importance of demographic and cultural factors in shaping genetic diversity among the groups under study. A combination of small initial effective size and continued genetic isolation from surrounding populations seems to provide a coherent explanation for the diversity observed among Sauris, Sappada and Timau, which was found to be substantially greater than in other groups of European isolated populations. Simulations of micro-evolutionary scenarios indicate that ethnicity might have been important in increasing genetic diversity among these culturally related and spatially close populations.

Spatially Explicit Models to Investigate Geographic Patterns in the Distribution of Forensic STRs: Application to the North-Eastern Mediterranean

“…We used two demographic models modified from that of Capocasa et al [80] and graphically outlined in S9 Fig. In Model 1, a number of populations (initially set at 14 to simulate Italian locations) split from a large pool (100,000 current gene copies) which has been growing at a rate of 0.020/generation, i.e.…”

“…Generation time was assumed to be 29 years [84]. Splitting times (in generations before present) were sampled from a UNIFORM(224:276) distribution, to account for the long time of the spread of the Neolithic cultural package in the Italian peninsula [49], and deme sizes (in gene copies) were sampled from a UNIFORM(800:2400) distribution, to account for the autosomal effective size and larger census size as compared to Capocasa et al [80]. These demes were set to grow at a rate of 0.017/generation, continuing to exchange gene copies with the main pool at rates of 1.0E-3 and 1.0E-4 for sending and receiving, respectively.…”

Spatially Explicit Models to Investigate Geographic Patterns in the Distribution of Forensic STRs

“…In order to test the observed fixation indices against neutral evolutionary scenarios, coalescent simulations were obtained with Fastsimcoal2 (Excoffier & Foll 2011). We used two demographic models modified from that of Capocasa et al (2013) and graphically outlined in Supplemental Fig. 9.…”

“…Generation time was assumed to be 29 years (Fenner 2005). Splitting times (in generations before present) were sampled from a UNIFORM(224:276) distribution, to account for the long time of the spread of the Neolithic cultural package in the Italian peninsula (Malone 2003), and deme sizes (in gene copies) were sampled from a UNIFORM(800:2400) distribution, to account for the autosomal effective size and larger census size as compared to Capocasa et al (2013). These demes were set to grow at a rate of 20/47 0.017/generation, continuing to exchange gene copies with the main pool at rates of 1.0E-3 and 1.0E-4 for sending and receiving, respectively.…”

Overcoming the dichotomy: new insights into the genomic diversity of open and isolated European populations

“…A number of studies has investigated the effects of isolation in human populations by exploiting the high sensitivity to drift of unilinear markers of mtDNA and the non-recombining portion of the Y chromosome 4,5,6,7,8,9 . However, the lack of recombination limits the power of these genetic systems in the detection of signatures of genetic isolation in different historical and demographic conditions.…”