Allelic variation of the dopamine receptor D4 gene polymorphic region in gibbons

We examined the tandem repeat sequence of the dopamine receptor D4 (DRD4) gene in 73 individuals derived from 8 species of gibbons (genusHylobates) in an attempt to assess the variability of this gene in gibbon species.H. syndactylus (subgenusSymphalangus) andH. concolor (subgenusNomascus), which were inferred to have diverged at an early time within the family Hylobatidae, shared only long repeat (7-8) alleles. On the other hand, DRD4 was highly polymorphic in gibbons of the subgenusHylobates, with 4-, 5-, 6-, 7-, and 8-repeat alleles being recognized. In this subgenus, 4- and 5-repeat alleles were found in the species distributed mainly in the southern islands such as Sumatra, Java, and Borneo but not in the species inhabiting the Asian continent. Sequence analysis indicated that the repeat structure of the gibbon DRD4 gene was quite complex but most of the 48-bp units could be classified into several groups across the species based on sequence similarities. However, the sequence of the 7-repeat allele ofH. muelleri was unique, since the repeat units had low similarities to other units of gibbons.