Structural variation
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Genomic structural variation is the variation in structure of an organism's chromosome, such as deletions, duplications, copy-number variants, insertions, inversions and translocations. Originally, a structure variation affects a sequence length about 1kb to 3Mb, which is larger than SNPs and smaller than chromosome abnormality (though the definitions have some overlap).[1] However, the operational range of structural variants has widened to include events > 50bp.[2] Some structural variants are associated with genetic diseases, however most are not.[3][4] Approximately 13% of the human genome is defined as structurally variant in the normal population, and there are at least 240 genes that exist as homozygous deletion polymorphisms in human populations, suggesting these genes are dispensable in humans.[4] While humans carry a median of 3.6 Mbp in SNPs (compared to a reference genome), a median of 8.9 Mbp is affected by structual variation which thus causes most genetic differences between humans in terms of raw sequence data.[4]