In this paper, the structure of a southeastern Spanish population was studied for the first time with respect to its inbreeding patterns and its relationship with demographic and geographic factors. Data on consanguineous marriages from 1900 to 1969 were taken from ecclesiastic dispensations. Our results confirm that the patterns and trends of inbreeding in the study area are consistent with those previously observed in most non-Cantabrian Spanish populations. The rate of consanguineous marriages was apparently stable between 1900 and 1935 and (...) then sharply decreased since 1940, which coincides with industrialization in Spain. A marked departure from Hardy-Weinberg expectations in the ratio of first cousin to second cousin marriages in the study population was observed. The high levels of endogamy and its significant steadiness throughout the twentieth century is noteworthy. Accordingly, our results show that exogamous marriages were not only poorly represented but also that this reduced mobility suggests that the choice of a mate was preferentially local. We found higher mobility in M22 with respect to M33 cousin mating. The relationships between population size and consanguinity rates and inbreeding fit power-law distributions. A significant positive correlation was observed between inbreeding and elevation. Many Spanish populations have experienced a prolonged and considerable isolation across generations, which has led to high proportions of historical and local endogamy that is associated, in general, with high \ values. Thus, assessing genomic inbreeding using runs of homozygosity in current Spanish populations could be an additional pertinent strategy for obtaining a more refined perspective regarding the population history inferred from the extent and frequency of ROH regions. (shrink)

SummaryPedigree structures of 161 uncle/niece-aunt/nephew and 4420 first cousin consanguineous marriages registered during the 19th and 20th centuries in two large and very different Spanish regions have been analysed and their genetic consequences evaluated. The frequencies of the different pedigree subtypes within each degree of relationship were quite similar in both populations despite significant heterogeneity in inbreeding patterns. The mean X-linked inbreeding coefficient for each type of cousin mating was calculated and compared to that expected for autosomal genes. The effect (...) of genealogical structure on theFx/Fradio was compared to different cultural populations worldwide. Preferentiality and avoidance of close consanguinity along with specific types of pedigrees are discussed on the basis of premarital migration and sociocultural rules still deeply rooted in certain human groups. By admitting that the observedFxcoefficient is usually higher thanFin most human populations some remarks have been made in terms of population genetic risk. (shrink)