Copy number variation (CNV) is a significant source of genetic diversity in human and other mammalian genomes. Initially thought to be rare and associated with specific genetic disorders, CNVs are now known to be widespread and may account for a substantial portion of genetic variation. CNVs can influence gene expression and contribute to normal phenotypic variation, as well as to disease susceptibility. Recent studies have identified numerous CNVs in healthy individuals, highlighting their role in genomic diversity. CNVs encompass various structural genomic variations, including duplications, deletions, and inversions. They often occur in regions containing segmental duplications, which are DNA fragments >1 kb found on the same or different chromosomes. These duplications can lead to CNVs that may not necessarily result in severe genetic disorders. The discovery of CNVs has been facilitated by advances in genomic technologies, such as array-based comparative genomic hybridization (array CGH) and fosmid end sequence mapping. Studies have shown that CNVs are more prevalent in regions with segmental duplications, and that these regions may be involved in structural rearrangements through non-allelic homologous recombination (NAHR). CNVs can also arise from non-homology-based mutational mechanisms and may be associated with non-β DNA structures. The size of CNVs is often correlated with their association with segmental duplications, with larger CNVs more likely to be found in such regions. CNVs can have clinical implications, affecting gene expression and contributing to phenotypic diversity. They may also play a role in common diseases, such as diabetes, cancer, and heart disease. The functional significance of CNVs is increasingly recognized, with many genes involved in molecular-environmental interactions and immune responses being affected by CNVs. In other species, such as mice and chimpanzees, CNVs are also prevalent and may contribute to phenotypic differences. Comparative studies suggest that CNVs may have evolved through positive selection, with some lineage-specific CNVs contributing to the divergence between species. The evolutionary significance of CNVs is an active area of research, with ongoing efforts to catalog and characterize them in the human genome. The development of comprehensive CNV maps is a key goal in genomic research, aiming to understand their role in genetic variation, evolution, and disease. Various technologies, including array-based CGH and fosmid end sequencing, are being used to identify and validate CNVs. However, challenges remain in accurately interpreting CNV data, particularly in distinguishing between true CNVs and artifacts. Future research will focus on improving the resolution and accuracy of CNV detection, as well as integrating CNV data with other genomic information to better understand their impact on health and disease.Copy number variation (CNV) is a significant source of genetic diversity in human and other mammalian genomes. Initially thought to be rare and associated with specific genetic disorders, CNVs are now known to be widespread and may account for a substantial portion of genetic variation. CNVs can influence gene expression and contribute to normal phenotypic variation, as well as to disease susceptibility. Recent studies have identified numerous CNVs in healthy individuals, highlighting their role in genomic diversity. CNVs encompass various structural genomic variations, including duplications, deletions, and inversions. They often occur in regions containing segmental duplications, which are DNA fragments >1 kb found on the same or different chromosomes. These duplications can lead to CNVs that may not necessarily result in severe genetic disorders. The discovery of CNVs has been facilitated by advances in genomic technologies, such as array-based comparative genomic hybridization (array CGH) and fosmid end sequence mapping. Studies have shown that CNVs are more prevalent in regions with segmental duplications, and that these regions may be involved in structural rearrangements through non-allelic homologous recombination (NAHR). CNVs can also arise from non-homology-based mutational mechanisms and may be associated with non-β DNA structures. The size of CNVs is often correlated with their association with segmental duplications, with larger CNVs more likely to be found in such regions. CNVs can have clinical implications, affecting gene expression and contributing to phenotypic diversity. They may also play a role in common diseases, such as diabetes, cancer, and heart disease. The functional significance of CNVs is increasingly recognized, with many genes involved in molecular-environmental interactions and immune responses being affected by CNVs. In other species, such as mice and chimpanzees, CNVs are also prevalent and may contribute to phenotypic differences. Comparative studies suggest that CNVs may have evolved through positive selection, with some lineage-specific CNVs contributing to the divergence between species. The evolutionary significance of CNVs is an active area of research, with ongoing efforts to catalog and characterize them in the human genome. The development of comprehensive CNV maps is a key goal in genomic research, aiming to understand their role in genetic variation, evolution, and disease. Various technologies, including array-based CGH and fosmid end sequencing, are being used to identify and validate CNVs. However, challenges remain in accurately interpreting CNV data, particularly in distinguishing between true CNVs and artifacts. Future research will focus on improving the resolution and accuracy of CNV detection, as well as integrating CNV data with other genomic information to better understand their impact on health and disease.