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Abstract
We report the distribution of a previously described 9.1-kb insertion-deletion polymorphism located on chromosome 22. We analyzed 1,844 individuals sampled from 26 Mediterranean populations in mainland Italy, Sicily, Sardinia, Tunisia, Libya, Morocco, Egypt, Greece, and Albania. The 9.1 kb - allele is the prevalent allele in the North African (range, 0.530.56), Greek (0.51), and Albanian (0.66) populations, whereas the 9.1 kb + allele is most frequent in a mainland Italian town (0.55) and in all Sicilian and Sardinian towns and villages thus far tested, with marked fluctuation ranges of 0.53-0.78 and 0.56-0.80, respectively. In tests for HardyWeinberg equilibrium the genotype frequencies observed in Athens and in four of the nine towns in Sicily (but in none of the towns in Sardinia) departed highly significantly from the expected values. Identical results were found in the same towns for a second insertion-deletion polymorphism located on chromosome 22q13 at a distance compatible with a low incidence of recombination. The data, which are in good agreement with the different histories of the two islands (Sardinia and Sicily), are consistent with a westeast differentiation in Sicily and support the evidence for ancient gene flow from the Iberian peninsula to Sardinia.
KEY WORDS: GENOME DIVERSITY, MEDITERRANEAN POPULATIONS, ITALY SICILY SARDINIA, TUNISIA, LIBYA, MOROCCO, EGYPT, GREECE, ALBANIA, INSERTION-DELETION POLYMORPHISM.
We previously described a 9.1-kb insertion-deletion polymorphism located in chromosome region 22q11.2 (Siniscalco et al. 2000) within the immunoglobulin variable lambda (IgV λ) light-chain gene cluster (Kawasaki et al. 1997). Polymerase chain reaction (PCR) and sequencing data show that the event, insertion or deletion, occurred only once (Robledo et al. 2002). Furthermore, a genome analysis in nonhuman primates suggests that the ancestral state is the presence of the 9.1-kb sequence and that the polymorphism is due to a deletion in the human lineage (Robledo et al. 2004). The combined evidence of a unique occurrence of the polymorphism and the knowledge of its ancestral state makes this marker a powerful tool for population genetics studies.
A human population screening showed a worldwide occurrence of the polymorphism (Robledo et al. 2002): The highest frequencies of the 9.1 kb - allele, in some cases approaching fixation, were observed in several distinct populations living in Oceania (Robledo et al. 2003). On the other hand, preliminary...