10.4 Evidence of introgression

Discordant trees can also be produced by introgression. In this case, the B allele arises on the Neanderthal lineage and is passed from Neanderthals into a human population, creating either an ABBA or BABA pattern (depending on which population receives Neanderthal gene flow).

Fig. 4. ABBA and BABA allele patterns formed by Neanderthal introgression.

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