Studio della variabilità genetica di popolazioni di Capra Hircus europee e del bacino del Mediterraneo mediante marcatori molecolari AFLP
Author(s)
Bernardi, Jamila
Date Issued
May 10, 2006
Type
Doctoral Thesis
Abstract
Goats are the most adaptable and widely spread ungulate livestock species in the world and they are an important source of milk, meat, skin and fibre. Moreover they have played a central role in the Neolithic agricultural revolution and in the spread of human civilization. The knowledge of goats evolutionary history and of the partition of the genetic variability within and among breeds in this species is fundamental for planning strategies for conservation. Molecular techniques have provided useful markers for the study of genetic variation in this species, such as microsatellite loci, mitochondrial DNA polymorphism and amplified fragment polymorphism (AFLP).
AFLP markers, a technique based on restriction and amplification of genomic DNA, were used to investigate the genetic variation in a sample of domestic goat (Capra hircus) derived from Europe and Near East (Jordan and Saudi Arabia).
A total of 1304 individuals and 47 breeds are collected and analysed using three different AFLP primer combinations, necessary to obtain 101 markers. On the basis of allele frequencies estimated by a Bayesian approach are calculated both the expected heterozygosity and the Reynolds distances between populations.
The expected heterozygosity was not significantly different except for the breeds Valais Black Neck (Switzerland) and Angora (Turkey) against Dukati (Albania) and Carpathian (Romania) (p<0.5). The variability of AFLP loci was largely maintained within breeds, as suggested by the two coefficients Fst (0.0612) and average unbiased Gst (Nei and Chesser, 1983) (0.13). These values indicate that the most of the variability was within breeds (87%), while only the 13% of the difference is between breeds.
Factorial correspondence analysis (FCA) were performed to show the relationship between the individual belonging to each breed. This graphic representation showed that almost all the breeds cluster together, whereas two of them, Tauernschecken (Austria) and Orobica (Italy) are positioned very distant from the others. These results were confirmed by the. principal component analysis (PCA) based on Reynolds distances. The original genetic resource discovered in Orobica and Tauernschecken may reflect undocumented migration or numerous gene flows with wild goats. These breeds show the lower genetic distance values with the Eastern European breeds investigated and have probably been introduced in the Alps in historical time.
Genetic diversity of the goat populations investigated confirms what is expected on the basis of their geographical location (more variability is present near the domestication sites). Breeds sampled around the traditional centre of domestication (Fertile Crescent) cluster together and the other populations show a South-to-North distribution pattern. Principal Component Analysis of genetic distances and the geographic
distribution of goat diversity, highest in the Near and Middle East and declining in agreement with the routes of post-domestication human migrations, support the demic diffusion model of pastoralism.
The first two axes of variance, interpolated with geographic coordinates, display a clear gradient that is the signature of two independent events of goat migration, likely together with human population, or alternatively the combined effects of a probably ancient human migration and of more recent large scale trades.
The study of breeds of marginal rural areas is important to understand the priority of conservation of genetic resources. Using an integrated approach, as ECONOGENE project has done, is possible to contribute to understand the importance of animal genetic resources in marginal rural areas. An extensive portrait can be obtained only integrating data from different sources (climatology, geography, socio-economic sciences etc.). Such an integrated approach can lead to the definition of appropriate guidelines for the management and conservation of goats genetic resources.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
Subjects
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