Volume 1, Issue 1 , Pages 264-265, August 2008
Exploring mitochondrial DNA variation in the Italian Peninsula
Article Outline
- Abstract
- 1. Introduction
- 2. Materials and methods
- 3. Results
- 4. Discussion
- Conflict of interest
- References
- Copyright
Abstract
The genetic structure of Italy appears to be mainly shaped by pre-Roman historical events. The studies carried out so far show a major North–South cline, possibly the result of two distinct main demic processes: the first colonisation of the area during the Palaeolithic period and the subsequent Neolithic expansion from the Middle East. However, the demographic contribution of these events is still a matter of debate. We here report mitochondrial DNA (mtDNA) data from nine population groups covering the main Italian regions: Central Liguria (N
=50), East Friuli (N=51), South Latium (N=48), Central Marche (N=53), West Calabria (N=50), Central Campania (N=50), South Apulia (N=53), and two populations from Sicily (East and West Sicily, N=40 each). Haplogroup frequency spectra indicate clear differences at a regional level and haplotype sharing among populations is low.
Keywords: mtDNA, SNPs, Haplotypes, Italian Peninsula, Population substructure
1. Introduction
Distribution of genetic variation in Italy has been investigated by few studies. Barbujani et al. [1] explored the presence of genetic barriers within the peninsula by looking at autosomal data. Interestingly, the zones of sharp changes in gene frequency were reflected at both linguistic and geographical level. Mitochondrial DNA (mtDNA) analysis revealed the presence of clines within the peninsula [2], as previously shown also by autosomal data [3]. More recently, a Y-chromosome investigation identified a single major cline across the peninsula [4], but pointed to local drift and founder effect as main explanation for the observed distribution of genetic diversity. Other results [5] point to a distribution of genetic variation along a North to South axis and support a Demic Diffusion Model, a scenario due to the admixture of two different groups: the Mesolithic original inhabitants of the peninsula and the incoming Neolithic farmers.
2. Materials and methods
Samples were collected by mouth swabs and blood drawing. Extraction was performed with a modified salting-out method [6]. Genetic variation was investigated by both fast (mtDNA hypervariable segment I and II, HVS-I/II), and slow (SNPs) evolving markers. mtDNA has been characterized for the complete sequence of the control region (that includes the two hypervariable segments HVS-I/II) following conditions described by Salas et al. [7], and a selection of informative mtDNA coding region SNPs, genotyped as described in Quintáns et al. [8]. We here show some preliminary results based on the analysis of the HVS-I and SNPs. Analyses were undertaken on an ABI3100 Genetic Analyser (AB, AppliedBiosystem).
3. Results
Standard Statistics were calculated using Arlequin software version 3.1 [9]. A total of 435 individuals were sequenced for the HVS-I: 50 Central Liguria, 51 East Friuli, 48 South Latium, 53 Central Marche, 50 West Calabria, 50 Central Campania, 53 East Apulia, 40 both East and West Sicily. All the polymorphisms observed were nucleotide substitutions. The uniquely found haplotypes (K), the number of variable nucleotide positions (A), the nucleotide diversity (π) and the mean nucleotide pairwise differences (P) for each population are reported in Table 1. Total nucleotide diversity is 0.015. Mean nucleotide pairwise difference is 4.3±2.1. AMOVA analysis revealed a between population variation of 0.7% (Fst=0.00695, p<0.01). The 435 investigated sequences were clustered in 19 different haplogroups. We did not detect members of haplogroups H7 and R*.
Table 1. N=number of samples; K=number of different sequences found; A=number of variable nucleotide positions; π=nucleotide diversity; P=mean nucleotide pairwise differences
| Population | N | K | A | π | P |
|---|---|---|---|---|---|
| Central Liguria | 50 | 36 | 50 | 0.017±0.009 | 4.7±2.3 |
| East Friuli | 51 | 33 | 53 | 0.017±0.009 | 4.7±2.3 |
| South Latium | 48 | 26 | 34 | 0.011±0.006 | 3.1±1.6 |
| Central Marche | 53 | 44 | 54 | 0.015±0.008 | 4.3±2.2 |
| West Calabria | 50 | 40 | 51 | 0.015±0.008 | 4.2±2.1 |
| Central Campania | 50 | 33 | 47 | 0.017±0.009 | 4.7±2.3 |
| East Apulia | 53 | 44 | 44 | 0.014±0.007 | 3.8±1.9 |
| East Sicily | 40 | 30 | 42 | 0.016±0.009 | 4.6±2.3 |
| West Sicily | 40 | 26 | 36 | 0.016±0.009 | 4.5±2.2 |
4. Discussion
Values of nucleotide diversity and mean nucleotide pairwise differences are similar to those observed in other European populations (Table 1). AMOVA analysis does not show evidence of population stratification when considering the sequence range 16,090–16,365. Phylogeographic analysis however have allowed to dissect the populations into different lineages, revealing clear evidences of population substructure. The 435 investigated sequences were clustered in 19 different haplogroups. The salient features of the haplogroup distribution in the assigned sequences are the high frequencies of H (37.93%), U (14.5%), T (11.72%) and J (9.9%). Haplogroup frequency spectra indicates clear differences at a regional level; for instance, haplogroup J makes-up ∼20% in South Apulia (Southeast Italy) but only account for ∼2.5% and ∼7.5% of the mtDNAs in West and East Sicily (Southwest Italy), respectively. Haplogroup U is present in all regions from a maximum of 22% (South Latium) to 9% (Central Marche), but only account for 4% in West Sicily. We did not found haplogroup L in the south regions of the Peninsula (West Calabria, Central Campania, South Apulia) and also in Central Liguria. Haplogroup K is absent only in South Latium. We also noticed the presence of haplogroup I only in the southern regions, East Sicily and Central Marche. Haplotype sharing among populations is low, which is consistent with limited gene flow along the Italian Peninsula and supports the existence of substantial levels of population stratification (although Fst index is unable to detect it).
Conflict of interest
None.
References
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PII: S1875-1768(08)00163-7
doi:10.1016/j.fsigss.2007.10.119
© 2008 Elsevier Ireland Ltd. All rights reserved.
Volume 1, Issue 1 , Pages 264-265, August 2008
