brain, somatically derived copy number variations are frequent. Copy number variations show wide variability (9 to 100% of brain neurons in different studies). Most alterations are between 2 and 10 Mb in size with deletions far outnumbering amplifications. Copy number variations appear to be higher in brain cells than in other cell types. A likely source of copy number variation is incorrect repair of DNA damage. Genomic duplication and triplication of the gene appear to be a rare cause of Parkinson's disease, although more common than point mutations. Copy number variants in RCL1 gene are associated with a range of neuropsychiatric phenotypes in children. Gene families, and natural selection Recently, there had been discussion connecting copy number variations to gene families. Gene families are defined as a set of related genes that serve similar functions but have minor temporal or spatial differences and these genes likely derived from one ancestral gene. The main reason copy number variations are connected to gene families is that there is a possibility that genes in a family may have derived from one ancestral gene which got duplicated into different copies. Mutations accumulate through time in the genes and with natural selection acting on the genes, some mutations lead to environmental advantages allowing those genes to be inherited and eventually clear gene families are separated out. An example of a gene family that may have been created due to copy number variations is the globin gene family. The globin gene family is an elaborate network of genes consisting of alpha and beta globin genes including genes that are expressed in both embryos and adults as well as pseudogenes. These globin genes in the globin family are all well conserved and only differ by a small portion of the gene, indicating that they were derived from a common ancestral gene, perhaps due to duplication of the initial globin gene. Research has shown that copy number variations are significantly more common in genes that encode proteins that directly interact with the environment than proteins that are involved in basic cellular activities. It was suggested that the gene dosage effect accompanying copy number variation may lead to detrimental effects if essential cellular functions are disrupted, therefore proteins involved in cellular pathways are subjected to strong purifying selection. In addition, proteins function together and interact with proteins of other pathways, therefore it is important to view the effects of