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How 23andMe Reports Genotypes

In the raw data, you can view your genotype at a particular location in your DNA. The raw data is presented in an uninterpreted format. This data has undergone a general quality review, however only a subset of markers have been individually validated for accuracy. As such, the data from the 23andMe Browse Raw Data feature is suitable only for research, educational, and informational use and not for medical or other use.

Base Pairs (A, C, T, G)  |  Insertions and Deletions  |  Strandedness 


Base Pairs

For most SNPs, genotypes will be reported as the set of nucleotides or the base pair found at that location. There are four types of bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

Insertions and Deletions

On occasion, one or more bases may be inserted into or deleted from the genetic code at a particular location. 

Depending on where in the genome the change is located, either an insertion or a deletion could represent the normal version of the variant. In other words, there are some places in the genome where having an extra base (insertion) is the normal variant, and having a deletion is the rare variant. Conversely, there are some places in the genome where having an insertion is rare, making a deletion the normal variant at that location.

Genotyping does not report on all possible insertions or deletions. In general, the ones reported on are small, spanning only one or a few bases.

Strandedness

The SNP genotypes in the Browse Raw Data feature might not match what you learn about the SNP from other sources such as dbSNP. This is because every SNP can be represented using either of the two DNA strands, and this representation will often differ from database to database or publication to publication.

For example, 23andMe might report that a SNP has two versions, G and A. But other sources may report that the versions are C and T. Because of the double-stranded nature of DNA, both ways of reporting the SNP are correct: G pairs with C on the opposite DNA strand, while A pairs with T.

All of the genotypes displayed in Browse Raw Data are oriented with respect to the positive strand on the reference assembly of the human genome (build 37). Note that this could be different from how the SNP is oriented in dbSNP, or how it might be presented in a publication.


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