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How do I use the Chromosome Browser for shared DNA segments?

The Chromosome Browser for shared DNA segments is a visual tool allowing you to locate the DNA segments you share with a DNA match.

Examining the shared segments is very helpful to the extent that it may prove genetic linkage between individuals. For example, if you map segments that you and other DNA matches share, you may discover that you all are descended from a common ancestor. If all shared segments are in the same genomic location, that common DNA was likely inherited from a single ancestor and can help you understand how all of you are related.

On the Chromosome Browser, if you place your mouse over each shared segment in purple, a pop up will appear with more information about this specific shared segment:

  • The Genomic position indicates the start and end location of the matching segment. There are millions of base pairs within a chromosome. The specific location of the base pair tells you where exactly where the segments starts and stops.
  • The rsID (Reference SNP cluster ID) is a number used by scientists to identify specific SNPs in the genome. 
  • The Segment size indicates the length of the matching segment between two people, measured in centiMorgans (cM). The longer the segment is, the higher the probability that you are related.
  • The Number of SNPs (Single Nucleotide Polymorphisms) within the matching segment. 

DNA segments can be found on all of the 22 autosomal chromosomes. The segment length is determined by the centiMorgan distance between the first SNP and the last SNP. The longer the shared segment is, the higher the probability that it was inherited from a common ancestor, which means that the two people are genetically related.

You can also download the shared DNA data into a CSV file if you click on ‘Advanced options’ on the right-hand side, then on ‘Download shared DNA info’:

Downloading the raw data of several of your DNA matches can be helpful if you want to map all the shared segments and check if they have the same genomic location. 

For more information about shared DNA, you can also read: What are Shared DNA segments?