In recent years, we have dramatically changed our view of human genome, from a collection of DNA base pairs that was largely quite stable to one whose very structure can change. We’ve learned that higher-order structural features, such as specific configurations of repeated base pair sequences, can predispose for DNA rearrangements.
One of the most intriguing types of DNA rearrangements is copy-number variants (CNVs), deletions or duplications of parts of the genome. While CNVs range in size from a few hundred base pairs to several mega-bases affecting the copy number of one to dozens of juxtaposed genes, they are not identifiable by conventional light microscopy. It was not until a few years ago that improved technology enabled us to perform high-resolution genome-wide surveys of CNVs in individual genomes. These surveys revealed a large amount of copy number variation (at least 12,000 CNVs overlapping more than 1,000 genes), most of which represent benign polymorphic changes. CNVs are classified as rare (occurring at a frequency of 1 percent in the population) or common; collectively they cover at least 12–13 percent of the genome in the general population.
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