Jews and Khazars

Askhenazi Jews have about 5% of Y haplogroup Q [1], which is lacking in Sephardic Jews and is thus probably not of ancient Jewish origin.

Haplogroup Q is found in Asia in very high frequencies in several Uralic and Altaic groups [2], so it's possible that it represents an introgression of Khazar elements; the Khazars were a Turkic tribe.

[1] Hum Genet (2004) 114 : 354–365
[2] Am. J. Hum. Genet., 74:661-682, 2004