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| It is important that the normalization results in a unique representation of the variant. Before we begin the proof, intuitively, accept that any representation of a variant can be | | It is important that the normalization results in a unique representation of the variant. Before we begin the proof, intuitively, accept that any representation of a variant can be |
− | transformed to another representation by removing or adding nucleotides from the reference sequence. | + | transformed to another representation by adding nucleotides from the reference sequence to either ends of all the alleles at the same time or removing equivalent nucleotides from the ends of |
| + | all the alleles at the same time. |
| + | |
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| Now suppose there are 2 normalized variants A and B. Suppose A is at a different position from B and B is to the right of A (without loss in generality), this is not possible because by the definition of a normalized variant, it is left aligned, | | Now suppose there are 2 normalized variants A and B. Suppose A is at a different position from B and B is to the right of A (without loss in generality), this is not possible because by the definition of a normalized variant, it is left aligned, |
| and if they were at different positions, that means B may be left aligned to A since they represent the same variants leading to a contradiction. So A and B must be at the same position. | | and if they were at different positions, that means B may be left aligned to A since they represent the same variants leading to a contradiction. So A and B must be at the same position. |
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− | Now, suppose that A and B are of different lengths where B is longer than A, then this is not possible as B is then not parsimonious, so B can be trimmed to the same length as A. | + | |
| + | Now, suppose that A and B are at the same position but are of different lengths where B is longer than A (without loss in generality), this is not possible as B is then not parsimonious, so B can be trimmed to the same length as A. |
| + | |
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| Thus A and B have to be at the same position and have the same length and variant normalization is unique. | | Thus A and B have to be at the same position and have the same length and variant normalization is unique. |
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| *GATK v3.1-1-g07a4bf8 | | *GATK v3.1-1-g07a4bf8 |
| *vt normalize v0.5 | | *vt normalize v0.5 |
| + | |
| + | = Here is an example where this normalization algorithm fails = |
| + | |
| + | We distinguish the concepts of normalization and decomposition/reconstruction of variants as follows: |
| + | |
| + | |
| + | Normalization involves reducing representations of a variant to a canonical representation. Normalization can be applied to biallelic variants or multiallelic variants. The problem of normalization is solvable and there exists a unique representation that is left aligned and parsimonious. Mathematical proof is published. [http://bioinformatics.oxfordjournals.org/content/suppl/2015/02/19/btv112.DC1/VtNormApplicationNote_supp_20141113_1346.pdf] |
| + | |
| + | |
| + | Decomposition of variants involves the breaking down of a variant record into multiple records. It may be done vertically - as in multiallelics becoming biallelics or it can be done horizontally - a cluster of indels and SNPs represented as a complex variant being splitted up into several records. Horizontal decompositions in general do not have a unique solution. Similarly, reconstruction combines several variant records into a single record and can be done vertically and horizontally too. Vertical decomposition of a multiallelic variant to a set of biallelic records is a many to one function. Construction of a set of biallelic variants into a multiallelic record is not unique as you need to considered all possible permutations of the haplotypes containing your alleles. |
| + | |
| + | |
| + | If your example contains the decomposition or reconstruction of variants, then it is probable that you can find inconsistencies. |
| + | |
| + | |
| + | It is important to distinguish the difference between normalization and decomposition/reconstruction. The notion of normalization implies that a variant can be reduced to a standardized form. If you were to include decomposition and reconstruction in your notion of normalization, you are bound to find inconsistencies simply due to the inherent issues of identifiability. |
| + | |
| + | |
| + | When performing decomposition and construction, I think the following factors should be considered: |
| + | |
| + | * Are your variants describing just a single individual or a population? |
| + | * Are the genotypes (if any) in your individual(s) phased? |
| + | |
| + | Depending on the context, you will obtain different answers. |
| + | |
| + | [https://github.com/atks/vt/issues/16 An example of inconsistent variant representation due to using vt normalize] |
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| = Citation = | | = Citation = |
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− | [http://bioinformatics.oxfordjournals.org/content/early/2015/02/19/bioinformatics.btv112.abstract?keytype=ref&ijkey=2kB1TkBGzkoP1gd Adrian Tan, Gonçalo R. Abecasis and Hyun Min Kang. (2015) Unified Representation of Genetic Variants. Bioinformatics. doi: 10.1093/bioinformatics/btv112 ] | + | [http://bioinformatics.oxfordjournals.org/content/31/13/2202 Adrian Tan, Gonçalo R. Abecasis and Hyun Min Kang. (2015) Unified Representation of Genetic Variants. Bioinformatics.] |
| + | |
| + | = Translations = |
| + | |
| + | A mandarin translation can be found [http://www.lyon0804.com/fan-yi-variant-normalization.html here] |
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| = Maintained by = | | = Maintained by = |
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| This page is maintained by [mailto:atks@umich.edu Adrian]. | | This page is maintained by [mailto:atks@umich.edu Adrian]. |