[Genetic demographic study of Zulia State, Venezuela, by isonymy].

The genetic structure of Zulia State, Venezuela, was studied through the distribution of surnames from individuals above 40 years of age, obtained from the register of electors. The sample studied consisted in 440, 190 individuals and 10,423 different surnames. For each of the 81 counties of the State, the following estimators were calculated: percentage of the population included in surnames which appear only once (estimator A), percentage of the population included in the seven most frequent surnames (estimator B), the coefficient of consanguinity due to random isonymy phi ii, and Karlin and McGregort's ni (v), an estimator of migration. The correlation between phi ii and B was 0.92, indicating that 85% of the variation observed in the coefficient of consanguinity due to random isonymy is due to the seven most frequent surnames. The correlation between A and ni was 0.93, so that 86% of the variation observed in ni, is due to surnames which appear only once. On the other hand, correlations between A and B, and between phi ii and v were non significant (-0.08 and -0.17 respectively), meaning that they are measuring different features of population structure: B and phi ii, isolation, while A and v, migration. The most isolated counties of Zulia are localized towards the northwestern portion of the State, within the Venezuelan Guajira, although relative isolation is also observed in the southern counties. Isolation by distance is estimated through the correlation between the logarithmic transformations of Euclidean and geographic distances, giving a value of 0.63. This high value might be partially due to the barrier effect of the Lake of Maracaibo. Eight surnames with a focal distribution within Zulia were identified: Almarza, Badell, Bastidas, Bohórquez, Cardozo, Carmona, Espina and Matos. Carriers of these surnames have a high probability of having their origin at the counties where they are localized.