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Description
The present Venezuelan population is the product of crosses between Amerindians, Europeans, mostly Spaniards, and Africans, who entered into contact five centuries ago and then interacted and mixed. Spaniards have been coming to Venezuela continuously since the conquest, and during the last century other Europeans, mainly Italians and Portuguese, have also contributed to the Venezuelan gene pool. African migration, mainly from the sub-Saharan region, was limited to the 16th, 17th, and 18th centuries, the period in which slave trade was most active. Caracas, the capital of Venezuela, was founded in 1567 and has been an important economic pole of attraction for inhabitants from the entire country and from abroad, but the admixture process within Caracas has been heterogeneous throughout the different socioeconomic levels. During the 17th century, Spanish founders and their descendants had a privileged position and kept the political domain of the city while the natives lived in the suburbs and the Africans were slaves or domestic servants (Acosta Saignes 1967). However, Spanish people of Canarian origin have also been reported as living in the suburbs (Cunill Grau 1987). During the 18th century, interethnic crossing was evident, and the pardos, the product of these crosses for several generations, joined the natives on the outskirts of Caracas. At the beginning of the 20th century, oil production caused a massive national immigration to the city, which had a strong influence on the socioeconomic distribution of its inhabitants; the poorer showed a tendency to settle in the western section of Caracas, and the wealthier migrants settled in the eastern section. During the 1940s and 1950s, after World War II, Spaniards, Italians, and Portuguese arrived in Caracas; most of them engaged in commercial activities. Immigration from South America, mainly from Colombia, was also important during the 1970s. Thus the population of Caracas has become strongly stratified, with evident genetic and cultural admixture.
As part of a project related to the genetic structure of the Venezuelan population, we decided to estimate admixture in samples from Caracas's low and high socioeconomic levels and to evaluate their differences, using the ABO and Rh (CDE) blood groups and three autosomal short tandem repeat (STR) sequences (FES/FPS, VWA, F13A01). Y-chromosome and mtDNA haplogroups were also studied to detect any sexual asymmetry in the admixture process, as observed in other Latin American populations (Alves-Silva et al. 2000; Carvajal-Carmona et al. 2000; Martinez-Marignac et al. 2004; Sans 2000).
Materials and Methods
Caracas is localized in the north-central part of Venezuela, at 10[degrees] 30' N and 66[degrees] 60' W, with a population of 2,758,917 inhabitants in 2001 (Instituto Nacional de Estadistica 2002).
Blood samples from 50 and 60 unrelated individuals up to second degree, living in Caracas, were selected in 2002 from the blood bank of the main public maternity clinic of the city (low socioeconomic level) and from the blood bank of the private clinic El Avila (high socioeconomic level), respectively. An informed consent form, approved by the Bioethics Committee of the Instituto Venezolano de Investigaciones Cientificas, was signed by each individual. Socioeconomic level was measured according to Graffar's (1956) method, modified for the Venezuelan population by Mendez Castellanos and de Mendez (1994). The method takes into account four variables: profession of the head of the family, level of instruction attained by the mother, main source of family income, and general conditions of the household. This method is widely used in Venezuelan social studies.
Blood samples were collected by venipuncture into tubes containing EDTA. The samples were stored at 5[degrees]C and brought to our laboratory packed in ice within three days after collection, where ABO and Rh (CDE) were typed based on standard immunological procedures.
DNA was extracted (Debomoy and Nurnberger 1991) and stored in alcohol until used. The microsatellites FES/FPS, VWA, and F13A01 were amplified using a multiplex system according to the manufacturer's recommendations, using the Gene Print STR systems (Promega Corp., Madison, Wisconsin) in a MiniCycler thermocycler (M. J. Research, Waltham, Massachusetts). The PCR products were typed using vertical electrophoresis on denaturing polyacrylamide gels and silver staining.
mtDNA haplogroups were defined using the following restriction enzymes: +663 HaeIII, +2349 DpnII, +3592 HpaI, -5176 AluI, -7025 AluI, -8616 DpnII, +10394 DdeI, -13259 HincII, and the 9-bp deletion in the intragenic region COII/tRN[A.sup.Lys]. These restriction enzymes allow the identification of continent-specific haplogroups: Amerindian haplogroups (A, B, C, and D), the main European (H) and sub-Saharan African haplogroups (L1 + L2, L3d, and L3e), and other haplogroups (I, J, K, T, U, V, W, X), which are also indicative of European ancestry (Table 1). Primers were synthesized... |
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