The dopamine D4 receptor (DRD4) gene exhibits a large amount of expressed p
olymorphism in humans. To understand the evolutionary history of the first
exon of DRD4-which in humans contains a polymorphic 12bp tandem duplication
, a polymorphic 13bp deletion, and other rare variants-we examined the homo
logous exon in thirteen other primate species. The great apes possess a var
iable number of tandem repeats in the same region as humans, both within an
d among species. In this sense, the 12bp tandem repeat of exon 1 is similar
to the 48bp VNTR of exon 3 of DRD4, previously shown to be polymorphic in
all primate species examined. The Old World monkeys show no variation in le
ngth, and a much higher conservation of amino acid sequence than great apes
and humans. The New World monkeys show interspecific differences in length
in the region of the 12bp polymorphism, but otherwise show the higher cons
ervation seen in Old World monkeys. The different patterns of variation in
monkeys compared to apes suggest strong purifying selective pressure on the
exon in these monkeys, and somewhat different selection, possibly relaxed
selection, in the apes. (C) 2000 Wiley-Liss, Inc.