We have examined the worldwide distribution of a
Y-chromosomal base-substitution polymorphism, the T/
C transition at SRY-2627, where the T allele defines
haplogroup 22; sequencing of primate homologues
shows that the ancestral state cannot be determined unambiguously
but is probably the C allele. Of 1,191 human
Y chromosomes analyzed, 33 belong to haplogroup
22. Twenty-nine come from Iberia, and the highest frequencies
are in Basques (11%; ) and Catalans n = 117
(22%; ). Microsatellite and minisatellite (MSY1) n = 32
diversity analysis shows that non-Iberian haplogroup-
22 chromosomes are not significantly different from Iberian
ones. The simplest interpretation of these data is
that haplogroup 22 arose in Iberia and that non-Iberian
cases reflect Iberian emigrants. Several different methods
were used to date the origin of the polymorphism: microsatellite
data gave ages of 1,650, 2,700, 3,100, or
3,450 years, and MSY1 gave ages of 1,000, 2,300, or
2,650 years, although 95% confidence intervals on all
of these figures are wide. The age of the split between
Basque and Catalan haplogroup-22 chromosomes was
calculated as only 20% of the age of the lineage as a
whole. This study thus provides evidence for direct or
indirect gene flow over the substantial linguistic barrier
between the Indo-European and non–Indo-European
–speaking populations of the Catalans and the
Basques, during the past few thousand years.