From “Saxons, Vikings and Celts – The Genetic Roots of Britain and Ireland” by Bryan Sykes:

A few years ago, researchers from Oxford found a Y chromosome that was very widespread throughout Asia, more or less within the geographical limits of the Mongol Empire. Finding a particular Y-chromosome with a specific fingerprint across such a wide area is highly unusual. Y-chromosomes are generally much more localized. The explanation, which I think is the correct one, is that this is the Y-chromosome of the first Mongol emperor, Genghis Khan, who lived in the first half of the thirteenth century. Not only is the Y-chromosome fingerprint geographically dispersed, it is also very common. In Mongolia, for example, 8 per cent of men have inherited the Genghis chromosome. If you compute the number of men who carry this Y-chromosome throughout Asia, and occasionally on other continents, then it comes to a staggering 16 million. Even a cursory glance at Genghis Khan's methods in warfare is enough to understand the genetic mechanism. On conquering an enemy's territory he would kill all the men, then systematically inseminate all the good-looking women - he left his commanders strict instructions on that point. When he died, the custom of patrilineal inheritance ensured that his empire was distributed among his sons, and their sons. Thus his Y-chromosome increased with each generation of male descendants, who inherited not only a portion of his wealth but also, presumably, his attitude to women. Though we have no historical records of men with quite such sexual predominance in the Isles, the confusion of minor kings is just the sort of condition where one might expect to discover the Genghis effect.