What to say about a match in many chromosomes

Question

When I look at the list of my DNA matches in Gedmatch, most people share only one of the 22 pairs of chromosome, a few share two. I found one person sharing as many as 5 chromosomes. What does that tell me about that person? Thanks.

Answer 1

The number of chromosomes alone will not tell you anything much. What you need to consider is the size of the match (number of cMs) and which segments. The size of the match will help you to determine how close the relationship may be and you can use the segment information in grouping matches to help identify common ancestors.

Comments

Thanks a lot.

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Harry, Thanks for the best answer star.

Answer 2

As Lynda mentions, the number of chromosome pairs on which matches occur isn't particularly significant in determining a relationship. There are two "lengths" which are used for matching on gedmatch:

- a single sequence of length 7 cM or more on a single chromosome pair that is identical for two persons is a "match"
- the sum of the lengths of all such matches is the total length.

The total length of all matches provides an indication of the relationship (2nd cousin, great-grandparent, etc). So the number of chromosome pairs on which matches occur isn't used to indicate a relationship. However, a larger number of matches contributes to the total length, which is an indication.

Matches across several pairs of chromosomes is very useful, however, when you start mapping chromosomes to determine on which chromosome (X or Y) of the pair the match occurs. So, more is better for that reason.