A total of 6 CNV genes were identified to be tissue-specific in their expression (Table 5). Most of these genes (67%) were found in the testes. The most abundant gene family represented in this set, including 2 of the 4 genes, was the neuroblastoma breakpoint family (NBPF). Genes belonging to this family are involved in transporting RNA between the cell nucleus and the cytoplasm. NBPF genes have been shown to be copy number variable in humans and other primates (Vandepoele et al., 2005). This gene family has been shown to be expressed in the testes of humans (Vandepoele and van Roy, 2007) and is hypothesized to play a role in male reproduction (Vandepoele et al., 2005). The testis is a tissue that has a high level of interaction with the environment. Environmental factors, such as interference with testicular cooling and endocrine disruptors, are known to influence the development and function of the testes (Sharpe and Franks, 2002). Our finding tissue-specific CNV genes in the testes is perhaps not coincidental. It has been argued in previous studies that copy number variation is the result of positive selection for a diverse set of proteins that can meet the challenges of a constantly changing environment (Kondrashov and Kondrashov, 2006).