From Wikipedia

Highland Clans

Clan MacDonald

Clan Donald is one of the largest Scottish clans. There are numerous branches to the clan. Several of these have chiefs recognised by the Lord Lyon King of Arms; these are: Clan Macdonald of Sleat, Clan Macdonald of Clanranald, Clan MacDonell of Glengarry, Clan MacDonald of Keppoch, and Clan MacAlister. Notable branches without chiefs so-recognised are: the McDonnells of Antrim, the MacDonalds of Dunnyveg, MacDonalds of Lochalsh, the MacDonalds of Glencoe, and the MacDonalds of Ardnamurchan.

The Norse-Gaelic Clan Donald traces its descent from Dòmhnall Mac Raghnuill (d. circa 1250), whose father Reginald or Ranald was styled "King of the Isles" and "Lord of Argyll and Kintyre". Ranald's father, Somerled was styled "King of the Hebrides", and was killed campaigning against Malcolm IV of Scotland at the Battle of Renfrew in 1164. Clan Donald shares a descent from Somerled with Clan MacDougall, who trace their lineage from his elder son, Blake Donald.

Gaelic tradition gave Somerled a Celtic descent in the male line, as the medieval Seanachies traced his lineage through a long line of ancestors back to Colla Uais and Conn of the Hundred Battles. Thus Clan Donald claimed to be both Clann Cholla and Siol Chuinn (Children of Colla and Seed of Conn). Possibly the oldest piece of poetry attributed to the MacDonalds is a brosnachadh (an incitement to battle) which was said to have been written in 1411, on the day of the Battle of Harlaw. The first lines of the poem begin "A Chlanna Cuinn cuimhnichibh / Cruas an àm na h-iorghaile," (Ye children of Conn remember hardihood in the time of battle). A later poem made to John of Islay (1434 – 1503), last of the MacDonald Lords of the Isles, proclaims "Ceannas Ghàidheal do Chlainn Cholla, còir fhògradh," (The Headship of the Gael to the family of Colla, it is right to proclaim it), giving MacDonald's genealogy back to Colla Uais.

However a recent DNA study has shown that Somerled may have been of Norse descent in his male line. By testing the Y-DNA of males bearing the surnames MacDonald, MacDougall, MacAlister, and their variants it was found that a substantial proportion of men tested shared the same Y-DNA and a direct paternal ancestor. This distinct Y-chromosome R1a1 haplotype found in Scotland has been regarded as often showing Norse descent in the British Isles. According to the Clan Donald DNA Project about 22% of tested participants have this signature of Somerled.