Difference between revisions of "Variant classification"

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(Simple Biallelic Examples)
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: The alternate sequence is represented by a angled bracket tag.
 
: The alternate sequence is represented by a angled bracket tag.
  
= Simple Biallelic Examples =
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= Examples =
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We present the following examples to explain the concepts explained earlier.
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== Simple Biallelic Examples ==
  
 
     SNP<br>
 
     SNP<br>

Revision as of 10:19, 5 September 2014

Introduction

The Variant Call Format (VCF) is a flexible file format specification that allows us to represent many different variant types ranging from SNPs, indels to copy number variations. However, variant representation in VCF is non-unique for variants that have explicitly expressed reference and alternate sequences.

On this wiki page, we describe a a variant classification system for VCF variants.

Definitions

The definition of a variant is based on the definition of each allele with respect to the reference sequence. We consider 5 major types as follows.

1. SNP
The reference and alternate sequences are of length 1 and the base nucleotide is different from one another.
2. MNP
a.The reference and alternate sequences are of the same length and have to be greater than 1 and all nucleotides in the sequences differ from one another.
OR
b. all reference and alternate sequences have the same length.
3. INDEL
a. The reference and alternate sequence are not the same length.
AND
b. The removal of a subsequence of the longer sequence would reduce the longer sequence to the smaller sequence.
4. CLUMPED
5. SV
The alternate sequence is represented by a angled bracket tag.

Examples

We present the following examples to explain the concepts explained earlier.

Simple Biallelic Examples

   SNP
REF A ALT G
   MNP
REF AT ALT GC
   INDEL
REF AT ALT A
   SV
REF A ALT <DEL>

Complex Biallelic Examples

   SNP|INDEL
REF AT ALT G
   MNP|INDEL
REF ATT ALT GC
   MNP|CLUMPED
REF ATTTT ALT GTTTC
   INDEL|CLUMPED
REF ATTTTTTTT ALT GTTTC

Simple Multiallelic Examples

   SNP
REF A ALT G ALT C
   MNP
REF AG ALT GC ALT CT
   INDEL
REF ATTT ALT ATT ALT AT

Complex Multiallelic Examples

   SNP|MNP
REF AT ALT GT #SNP ALT AC #SNP #since all the alleles are of the sample length, classified as MNP too.
   MNP|CLUMPED
REF ATTTG ALT GTTTC #CLUMPED ALT ATTTC #CLUMPED #since all the alleles are of the sample length, classified as MNP too.
   SNP|MNP|INDEL
REF GT ALT CT #SNP ALT AG #MNP ALT GTT #INDEL
   SNP|MNP|INDEL|CLUMPED
REF GTTT ALT CG #MNP|INDEL ALT AG #MNP ALT GTGTG #SNP|INDEL|CLUMPED

SV Examples

 ======= Structural variants ========
 
          no. of structural variants         :      41217         
              2 alleles                      :           38079
                  deletion                   :                13135           <DEL>
                  insertion                  :                16451           <INS>
                     mobile element          :                    16253       <INS:ME>
                        ALU                  :                        12513   <INS:ME:ALU>
                        LINE1                :                         2911   <INS:ME:LINE1>
                        SVA                  :                          829   <INS:ME:SVA>
                     numt                    :                      198       <INS:MT>
                  duplication                :                  664           <DUP>
                  inversion                  :                  100           <INV>
                  copy number variation      :                 7729           <CN4>
              >=3 alleles                    :            3138
                  copy number variation      :                 3138           <CN4>,<CN8>

Output

Summarizes the variants in a VCF file

  #summarizes the variants found in mills.vcf
  vt peek mills.vcf
 usage : vt peek [options] <in.vcf>
 options : -o  output VCF file [-]
           -I  file containing list of intervals []
           -i  intervals []
           -r  reference sequence fasta file []
           --  ignores the rest of the labeled arguments following this flag
           -h  displays help
#This is a sample output of a peek command which summarizes the variants found in a VCF file.
  stats: no. of samples                     :          0
         no. of chromosomes                 :         22
========== Micro variants ==========
no. of SNPs  : 77228885 2 alleles (ts/tv)  : 77011302 (2.11) [52287790/24723512] 3 alleles (ts/tv)  : 216560 (0.75) [185520/247600] 4 alleles (ts/tv)  : 1023 (0.50) [1023/2046]
no. of MNPs  : 0 2 alleles (ts/tv)  : 0 (-nan) [0/0] >=3 alleles (ts/tv)  : 0 (-nan) [0/0]
no. Indels  : 2147564 2 alleles (ins/del)  : 2124842 (0.47) [683250/1441592] >=3 alleles (ins/del)  : 22722 (2.12) [32411/15286]
no. SNP/MNP  : 0 3 alleles (ts/tv)  : 0 (-nan) [0/0] >=4 alleles (ts/tv)  : 0 (-nan) [0/0]
no. SNP/Indels  : 12913 2 alleles (ts/tv) (ins/del)  : 412 (0.41) [120/292] (3.68) [324/88] >=3 alleles (ts/tv) (ins/del)  : 12501 (0.43) [7670/17649] (18.64) [12434/667]
no. MNP/Indels  : 153 2 alleles (ts/tv) (ins/del)  : 0 (-nan) [0/0] (-nan) [0/0] >=3 alleles (ts/tv) (ins/del)  : 153 (0.30) [138/465] (0.27) [67/248]
no. SNP/MNP/Indels  : 2 3 alleles (ts/tv) (ins/del)  : 0 (-nan) [0/0] (-nan) [0/0] 4 alleles (ts/tv) (ins/del)  : 2 (0.00) [3/5] (1.00) [3/3] >=5 alleles (ts/tv) (ins/del)  : 0 (-nan) [0/0] (-nan) [0/0]
no. of clumped variants  : 19025 2 alleles  : 0 (-nan) [0/0] (-nan) [0/0] 3 alleles  : 18508 (0.16) [12152/75366] (0.00) [93/18653] 4 alleles  : 451 (0.15) [369/2390] (0.33) [201/609] >=5 alleles  : 66 (0.09) [37/414] (1.19) [107/90]
====== Other useful categories =====
no. complex variants  : 32093 2 alleles (ts/tv) (ins/del)  : 412 (0.41) [120/292] (3.68) [324/88] >=3 alleles (ts/tv) (ins/del)  : 31681 (0.21) [20369/96289] (0.64) [12905/20270]
======= Structural variants ========
no. of structural variants  : 41217 2 alleles  : 38079 deletion  : 13135 insertion  : 16451 mobile element  : 16253 ALU  : 12513 LINE1  : 2911 SVA  : 829 numt  : 198 duplication  : 664 inversion  : 100 copy number variation  : 7729 >=3 alleles  : 3138 copy number variation  : 3138
========= General summary ==========
no. of reference  : 0
no. of observed variants  : 79449759 no. of unclassified variants  : 0

Maintained by

This page is maintained by Adrian.