One DNA study by Nebel found substantial genetic overlap among Israeli and Palestinian Arabs and Ashkenazi and Sephardic Jews. A small but statistically significant difference was found in the Y-chromosomal haplogroup distributions of Sephardic Jews and Palestinians, but no significant differences were found between Ashkenazi Jews and Palestinians nor between the two Jewish communities. However, a highly distinct cluster was found in Palestinian haplotypes. 32% of the 143 Arab Y-chromosomes studied belonged to this "I&P Arab clade", which contained only one non-Arab chromosome, that of a Sephardic Jew. This could possibly be attributed to the geographical isolation of the Jews or to the immigration of Arab tribes in the first millennium. Nebel proposed that "part, or perhaps the majority" of Muslim Palestinians descend from "local inhabitants, mainly Christians and Jews, who had converted after the Islamic conquest in the seventh century AD".