The GEDMatch ‘One-to-one’ compare page allows you to compare your results to one other person in the GEDMatch database.
Go to the GEDMatch website. Login to your account by entering your email and password and by clicking the Log in button.
From the GEDMatch dashboard, click the ‘One-to-one’ compare link in the Analyze Your Data area.
The next page is settings for the one-to-one comparison. In most cases, you should change two of the defaults. First, change the radio selection from Position Only to Graphics and Positions. Second, change the default “Minimum segment cM size to be included in total:” field to 10 (15 if you are Ashkenazi Jewish or another endogamous population).
The top of the one-to-one compare page has the key to the graphic (1), the information on who is being compared (2), and the settings that you used (3).
Matching segment information (1) shows for each chromosome. In the graphic, the non-matching, half matching, and fully matching SNP markers are on the top bar (2). The bottom bars shows where there are enough matching SNP markers to meet the cM threshold (3).
The matching segment information table has the following fields.
- Chr – The numbered chromosome.
- Start location – The position on the chromosome where the matching segment starts.
- End location – The position on the chromosome where the matching segment stops.
- Centimorgans (cM) – The measurement of centiMorgins (cM) in the segment.
- SNPs – The number of SNP markers compared for the segment.
When you share DNA from both your mother’s side and your father’s side with someone, you can have some segments that are fully identical. This is always the case with full siblings and double first cousins. It may also be the case when your parents are more distantly cousins.
You can find these areas on the one-to-one compare page by looking for green areas on the top part of the graphics.
Below, the graphic is annotated to show areas that don’t match (1, 5, and 9), areas that half match (2, 4, 6, and 8), and areas that fully match (3 and 7).
At the bottom of the one-to-one compare page, there is a summary of the matching between the two people.
In the next section, I will cover using the GEDMatch X ‘One-to-one’ page.