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Chromosome mapping

From ISOGG Wiki

Chromosome mapping is a technique used in autosomal DNA testing which allows the testee to determine which segments of DNA came from which ancestor. In order to map DNA segments on specific chromosomes it is necessary to test a number of close family relatives. Ideally one should test both parents, one of their children, and a number of first to third cousins on both the maternal and paternal sides of the family.

Not everyone has close relatives available for testing or has the funds to pay for such testing. Indeed, even if you did test all of your first and second cousins you might not be able to map your entire genome. In any case, the more first and second cousins you test, the higher the percentage of your genome that you can map, at least back to which parent or grandparent contributed any particular DNA segment.

Caution should be exercised when attempting to map smaller segments, and particularly segments under 15 cM because of the high false positive rate.[1]

Chromosome mapping with three siblings

   See main article: Visual phasing

Visual phasing is a methodology for assigning segments to specific grandparents based on the crossover points of three siblings. This technique can be employed when parents are not available for testing.

Blog posts and articles

Chromosome mapping tools

DNA Painter

   See main article: DNA Painter

DNA Painter, launched in 2018, is a popular freemium website provided by Jonny Perl which provides a chromosome mapping tool to track matching DNA segments across the different companies and identify patterns in the data. The first profile is provide free and a subscription is required to create up to fifty profiles and to access additional features.

Kitty Cooper's chromosome mapping tools

Kitty Cooper began providing visualisation tools for mapping DNA segments in 2013. The tools require input from a CSV file. A compact version of Kitty's segment mapper has been incorporated into GEDmatch. The following three tools are currently available:

Reviews relating to Kitty Cooper's tools

Borland Genetics HIR Mapper

   See main article: HIR Mapper (Borland Genetics)

  • The HIR Mapper is a tool in the Borland Genetics Web Tools and Database that automatically paints matches in the Borland Genetics database to phased (mono) kits as a chromosome map. The resulting map can be used on the site to extract the raw DNA on segments pertaining to specific ancestors. The maps are also compatible with DNA Painter and when using the HIR Mapper, the user has an option to import the results of the GEDmatch Segment Search tool if the user has created the same phased kit at GEDmatch.

Working with spreadsheets

In addition to the tools described above spreadsheets can also be used to track DNA segments. The matches spreadsheet should include the names and contact details of your matches, details of the matching segments and number of shared SNPs, the name of the most recent common ancestor and the known relationship. A number of genetic genealogists have provided Excel templates for chromosome mapping:

Presentations

References

  1. ↑ Bettinger B. A small segment round up. The Genetic Genealogist, 29 December 2017.

See also

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