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The Abbad are one of the largest tribes in Jordan with a complex structure dictated by historical and cultural factors. To study the genetic variability within the tribe, we examined four samples representing different levels of tribal structure for the polymorphisms of five blood groups, five erythrocyte enzymes, and seven serum proteins. The obtained allele distributions indicate a wide range of genetic variability within the tribe. An allelic heterogeneity test revealed significant differences between the examined samples, yet a gene diversity analysis revealed no significant substructuring. The observed genetic relationships among the four samples appear to agree with the tribal organization. Endogamous mating within the tribe and inbreeding within the subunits are believed to be the main factors that influenced the observed variability. This was confirmed by the results of the R matrix analysis, which summarized the genetic relationships in concordance with intertribal admixture, when affiliation and historical and maternal links were considered. The study is also an example of gene diffusion and of a negative relationship between the FY A — B — phenotype and endemicity of malaria.