A study identified 255 loci in the human genome with genomic imbalances among unrelated individuals. Twenty-four of these variants were present in more than 10% of the individuals examined. Half of these regions overlap with genes, and many coincide with segmental duplications or gaps in the human genome assembly. This heterogeneity may underlie human phenotypic variation and disease susceptibility, suggesting a more dynamic human genome structure. The study used array-based comparative genomic hybridization (array CGH) on 55 unrelated individuals to investigate large-scale copy-number variations (LCVs). The arrays contained selected large insert DNA fragments, distributed roughly every 1 Mb throughout the human genome. The study found 255 individual genomic clones with comparative gains or losses. Most of these clones were randomly distributed, with an average of 12.4 LCVs per individual. Of these, 102 LCVs occurred in more than one individual, and 24 were present in more than 10% of the individuals studied. The study found that 142 of the 255 polymorphic clones overlapped with known coding regions, and 67 clones encompassed one or more entire genes. This suggests that LCVs are not limited to intergenic or intronic regions. Fourteen LCVs were located near loci associated with human genetic syndromes or cancer. These variants may not directly cause genetic disease but could lead to chromosomal rearrangements or subtle phenotypic variation. The most common LCV encompassed the amylase alpha 1a and alpha 2a locus (AMY1A-AMY2A) at chromosome region 1p13.3. The study confirmed the array CGH results using various techniques, including FISH and quantitative PCR. The length of this polymorphic region ranged from 150 kb to 425 kb, and the study found that each LCV was confined to localized chromosomal regions. The study identified more than 200 LCVs in the human genome. Twenty-four of these variants were present in more than 10% of the individuals studied, and six were present at a frequency of more than 20%. The array platform used for these studies comprises only 12% of the total human genome sequence, so denser arrays may detect additional new genomic variations. The LCVs described here may have important functional effects on the evolution of the human genome. The study compiled all available information into a database, the Genome Variation Database, which will be a crucial resource for correlating genomic variations with experimental findings and clinical outcomes.A study identified 255 loci in the human genome with genomic imbalances among unrelated individuals. Twenty-four of these variants were present in more than 10% of the individuals examined. Half of these regions overlap with genes, and many coincide with segmental duplications or gaps in the human genome assembly. This heterogeneity may underlie human phenotypic variation and disease susceptibility, suggesting a more dynamic human genome structure. The study used array-based comparative genomic hybridization (array CGH) on 55 unrelated individuals to investigate large-scale copy-number variations (LCVs). The arrays contained selected large insert DNA fragments, distributed roughly every 1 Mb throughout the human genome. The study found 255 individual genomic clones with comparative gains or losses. Most of these clones were randomly distributed, with an average of 12.4 LCVs per individual. Of these, 102 LCVs occurred in more than one individual, and 24 were present in more than 10% of the individuals studied. The study found that 142 of the 255 polymorphic clones overlapped with known coding regions, and 67 clones encompassed one or more entire genes. This suggests that LCVs are not limited to intergenic or intronic regions. Fourteen LCVs were located near loci associated with human genetic syndromes or cancer. These variants may not directly cause genetic disease but could lead to chromosomal rearrangements or subtle phenotypic variation. The most common LCV encompassed the amylase alpha 1a and alpha 2a locus (AMY1A-AMY2A) at chromosome region 1p13.3. The study confirmed the array CGH results using various techniques, including FISH and quantitative PCR. The length of this polymorphic region ranged from 150 kb to 425 kb, and the study found that each LCV was confined to localized chromosomal regions. The study identified more than 200 LCVs in the human genome. Twenty-four of these variants were present in more than 10% of the individuals studied, and six were present at a frequency of more than 20%. The array platform used for these studies comprises only 12% of the total human genome sequence, so denser arrays may detect additional new genomic variations. The LCVs described here may have important functional effects on the evolution of the human genome. The study compiled all available information into a database, the Genome Variation Database, which will be a crucial resource for correlating genomic variations with experimental findings and clinical outcomes.