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An inversion is a chromosome rearrangement in which a segment of a chromosome becomes inverted within its original position. An inversion occurs when a chromosome undergoes a two breaks within the chromosomal arm, and the segment between the two breaks inserts itself in the opposite direction in the same chromosome arm.
In the human genome project the human genome was successfully sequenced, which provided a reference human genome for comparison of genetic variation. With improving sequencing technologies and the reference genome, more and more variations were found of several different sizes that were larger than 1 kb but smaller than microscopic variants.
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]
Copy number variation is a type of structural variation: specifically, it is a type of duplication or deletion event that affects a considerable number of base pairs. [2] Approximately two-thirds of the entire human genome may be composed of repeats [3] and 4.8–9.5% of the human genome can be classified as copy number variations. [4]
Schematic karyogram, with annotated bands and sub-bands as used in the International System for Human Cytogenomic Nomenclature of chromosomal rearrangements. It shows 22 homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two sex chromosomes, as well as the mitochondrial genome (at bottom left).
The human genome was the first of all vertebrates to be sequenced to such near-completion, and as of 2018, the diploid genomes of over a million individual humans had been determined using next-generation sequencing. [61] These data are used worldwide in biomedical science, anthropology, forensics and other branches of science.
Human genome projects are scientific endeavors that determine or study the structure of the human genome. The Human Genome Project was a landmark genome project. There are numerous related projects that deal with genetic variation (or variation in the encoded proteins), e.g. organized by the following organizations:
The typical human genome also contains 40,000 to 200,000 rare variants observed in less than 0.5% of the population that can only have occurred from at least one de novo germline mutation in the history of human evolution. [142] De novo mutations have also been researched as playing a crucial role in the persistence of genetic disease in humans.