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Subject: Re: [DNA] Need Help In Understanding and Using the Term "SNP"
Date: Tue, 30 Mar 2010 08:16:47 EDT


All lines in the 23andMe data (autosomes, X and Y included) are SNPs (or
small insertions/deletions, which behave like SNPs). A SNP is a spot in the
genome which is known to vary in the population. For instance, some people
have an A at position 73 in the mtDNA molecule, and some people have a G. The
alternative versions are called alleles.

In some places, you have the same allele as the CRS; in other places you
differ. Since most people match the CRS in over 99% of the positions, it's
customary to list just the places where you differ when you get a report from a
company like FTDNA. At 23andMe, everyone is tested for and sees the same
list of SNPs in the raw data; it's the allele column that will differ from
person to person.

Note that the base positions don't have to be absolute. If a person happens
to have an insertion at position 35 in the mtDNA molecule, that would throw
the numbering off. In order to keep the numbering standardized, that
mutation would be labeled 35.1G or whatever base was inserted. Then positions 36+
could still be aligned to the CRS.

Ann Turner

In a message dated 3/30/2010 4:15:50 AM Pacific Daylight Time,
writes:

> In this current "thread" I am trying to clear up my understanding as
> to whether each line in my 23andMe mtDNA download (2,153 lines)
> "corresponds to a SNP" as 23andMe states in the first few lines in
> the download or if only the "mutations" that I have in my mtDNA
> results are "SNPs" (as I understand the SMGF glossary states in their
> definition of a "SNP"). In my previous post (that you responded to) I
> gave the example that in the range from position 1 through position
> 304 I have 4 "mutations." My question is: Are only these 4 mutations
> SNPs or does every line of data in this range "correspond to a SNP"?


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