Is Per3 Polymorphic in Chimpanzees?

*Corresponding author e-mail: dany@psicobio.epm.br Introduction: Clock genes are conserved between eucoelomate animals. However, where invertebrates such as Drosophila have one copy of each clock gene, owing to gene duplication, vertebrates has gene families containing two or three members. Thus, whereas Drosophila has one Period gene, mammals have three ( Period1 , Period2 , and Periodd3 ). In all species studied, variability in circadian parameters has been associated with polymorphisms and mutations in clock genes. The human PER3 gene contains a variable number tandem repeat (VNTR) polymorphism in the coding region, where a 54-bp unit encoding 18 amino acids is repeated either four or five times. This polymorphism has been associated with diurnal preference and Delayed Sleep Phase Syndrome (DSPS), in studies performed both in the UK and in Brazil, and has been shown to associate with sleep homeostatic parameters both in the UK and in the USA. The VNTR in the Per3 gene appears to be exclusive to primates, but the number of repeated units differs between species. Some species, such as the gorilla and the Brazilian marmoset Callithrix jacchus have intraspecific polymorphism as found in humans, with 3/4 or 6/7 tandem copies, respectively. Methods: In order to investigate if an intraspecific polymorphism exists in the chimpanzee, we analyzed 42 samples of DNA extracted from individuals born in captivity after crossings between parents from different populations. Results/Conclusion: All DNA samples showed four repeat of the 54-bp unit, with no evidence for polymorphism. We conclude that the intraspecific polymorphisms found in humans and gorillas have probably occurred after the divergence of these species from their common ancestors with the chimpanzee. We are continuing the analysis of different primate species in order to understand better how the VNTR has expanded, and whether it influences circadian and sleep phenotypes in primate species other than humans. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil