Abstract
Since the reduced genetic diversity found in isolates should simplify the study of complex traits, analyses of patterns of homogeneity within populations are of particular interest. We analysed the mtDNA haplogroups and hypervariable segment I (HVS-I) sequences of 475 individuals from a geographically restricted and isolated area (Ogliastra) within Sardinia, comprehending 175 random samples from 20 out of 23 villages. The remaining 300 subjects were chosen from the other three villages, Talana, Urzulei and Perdasdefogu, by sampling all maternal lineages. A comparison with other European populations reveals that Ogliastra ranks among the most genetically homogenous population and that it has been small and isolated throughout its history. The lack of variation and the high genetic homogeneity indicate that an important founder event and a demographic expansion took place during the Neolithic (~ 7,700 years before present) in Ogliastra's mtDNA gene pool. We present highly resolved phylogenetic networks for Ogliastra and for the three sub-isolates. MtDNA differentiation in the sub-populations versus Ogliastra is revealed by a strong demarcation in their genetic pools due to distinctive founder effects and genetic drift. We found that genetic homogeneity strictly depends on a scale factor in population size and on sampling methodology. The outstanding homogeneity and the reduced female gene pool observed in Ogliastra, in the European context, hide an extremely marked differentiation in sub-isolates originated from the same archaic population. Although Ogliastra can be considered a genetically homogeneous isolate, small villages' divergent genetic histories underline the importance of more systematic analysis of DNA variation between and within populations.
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Acknowledgements
We thank Francesca Marras, Giuseppe Ledda and Antonella Demontis for their technical support in database consulting, genealogy and mtDNA analyses respectively. We are very grateful to the populations of Talana, Perdasdefogu and Urzulei for their collaboration, and to Parco Genetico dell'Ogliastra and the municipal administrations for their economic and logistic support.
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C. Fraumene and E. Petretto contributed equally to this work
Appendices
Electronic-database information
The URLs for data in this article are as follows:
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Genome Data Base, http://www.gdb.org/;
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Helsinki declaration, http://www.wma.net/e/policy/b3.html;
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Arlequin ver. 2.000: a software for population genetics data analysis — by Stefan Schneider, David Roessli, Laurent Excoffier of the Genetics and Biometry Laboratory, University of Geneva, Switzerland, http://lgb.unige.ch/arlequin/;
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Life Sciences and Engineering Technology Solutions, http://www.fluxus-engineering.com/ (for Network 3.0 software).
Appendix table
The variable positions within the HVS-I (16024–16383) sequences that were analysed for the Ogliastra, Talana, Urzulei and Perdasdefogu samples are as follows:
16030 | 16061 | 16126 | 16129 | 16145 | 16167 | 16169 | 16174 | 16188 | 16192 | 16193 | 16235 | 16240 | 16261 | 16269 | 16270 | 16292 | 16293 | 16294 | 16296 | 16298 | 16304 | 16311 | 16319 | 16320 | 16368 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Ref | C | T | T | G | G | C | C | C | C | C | C | A | A | C | A | C | C | A | C | C | T | T | T | G | C | T | |
1 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
2 | ° | ° | ° | ° | ° | ° | ° | G | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
3 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | G | ° | ° | ° | ° | ° | ° | ° | C | |
4 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | |
5 | ° | ° | ° | A | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | |
6 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | A | T | ° | |
H | 7 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | A | T | ° |
8 | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | A | T | ° | |
9 | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
10 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
11 | G | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
12 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | G | ° | G | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
13 | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
14 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | T | ° | ° | ° | ° | ° | ° | ° | |
15 | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
16 | ° | ° | ° | ° | A | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
1 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | |
2 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | |
3 | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | |
U | 4 | ° | ° | ° | ° | ° | ° | A | ° | ° | T | ° | G | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° |
5 | ° | ° | ° | ° | ° | ° | A | ° | ° | T | ° | ° | ° | ° | ° | T | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | |
6 | ° | ° | ° | ° | ° | ° | A | ° | ° | T | ° | G | ° | ° | ° | T | T | ° | T | ° | ° | ° | ° | ° | ° | ° | |
7 | ° | ° | ° | ° | A | ° | A | ° | ° | T | ° | G | ° | ° | T | T | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | |
8 | ° | ° | ° | ° | A | ° | A | ° | ° | T | ° | G | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
9 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | C | ° | ° | ° | ° | |
10 | ° | ° | ° | ° | A | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
1 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
2 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | |
J | 3 | ° | ° | C | ° | ° | T | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | ° |
4 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
5 | ° | ° | C | ° | A | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | |
1 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | ° | ° | |
V | 2 | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | C | ° | ° | ° | ° | ° |
3 | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | C | ° | ° | ° | T | ° | |
1 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | ° | ° | ° | ° | ° | |
2 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | ° | C | ° | ° | ° | ° | |
3 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | T | ° | ° | ° | ° | ° | ° | ° | |
T | 4 | ° | G | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | T | ° | ° | ° | ° | ° | ° | ° |
5 | ° | A | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | T | ° | ° | ° | ° | ° | ° | ° | |
6 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | T | T | ° | ° | ° | ° | ° | ° | |
7 | ° | ° | C | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | T | ° | T | T | ° | C | ° | ° | ° | ° | |
I | 1 | ° | ° | ° | A | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° | ° |
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Fraumene, C., Petretto, E., Angius, A. et al. Striking differentiation of sub-populations within a genetically homogeneous isolate (Ogliastra) in Sardinia as revealed by mtDNA analysis. Hum Genet 114, 1–10 (2003). https://doi.org/10.1007/s00439-003-1008-3
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DOI: https://doi.org/10.1007/s00439-003-1008-3