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-   -   # of SNP's in Small Segments Chromosome Browser (http://forums.familytreedna.com/showthread.php?t=42135)

kjsargent 27th July 2017 10:31 PM

# of SNP's in Small Segments Chromosome Browser
 
I was looking at a paper that was commenting on small segments showing up in children and not parents. The reported # of SNP's seems odd for most of the small segments 3cM or less. Exported all my matches and a significant number of these end in 00. (They are multiples of 100.) such as a segment 2.60 with 1100 SNP's matchings.

This can't correct, can it?

While I'm on the subject, is there a minimum number of SNP's for segments?

Thanx

John McCoy 28th July 2017 10:17 PM

I recently heard that FTDNA's matching algorithm works on groups of 100 adjacent SNP's. That's why counts here end in 00.

kjsargent 29th July 2017 11:09 AM

Thank you for responding,

I think this may be a bug because I don't think there are 500 SNP within a single 1cM Segment. The number is supposed to represent the number of SNP's that are compared between 2 locations. I highly doubt that there are EXACTLY 500 or 600, etc. This number seems to represent something else.

Also, these particular segments are found in a match to a child, but this segment is not shared with either parent, which is why I taking a close look at them.

georgian1950 29th July 2017 11:22 AM

Quote:

Originally Posted by kjsargent (Post 442249)
Thank you for responding,

I think this may be a bug because I don't think there are 500 SNP within a single 1cM Segment. The number is supposed to represent the number of SNP's that are compared between 2 locations. I highly doubt that there are EXACTLY 500 or 600, etc. This number seems to represent something else.

Also, these particular segments are found in a match to a child, but this segment is not shared with either parent, which is why I taking a close look at them.

Number of SNP's per cM varies.

kjsargent 29th July 2017 11:40 AM

I agree that the # of SNP's vary, which is why I am concerned.

I exported all my matches to excel and sorted on # of SNP's.

The # of SNP's is fairly well distributed except for 500,600, etc.

for example, I have 10,507 segments that are exactly 500 SNP's. There are almost exclusively for 3cM and smaller segments.


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