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
- 2 Blog posts and articles
- 3 Chromosome mapping tools
- 4 Working with spreadsheets
- 5 Presentations
- 6 References
- 7 See also
Chromosome mapping with three siblings
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
- Why map your chromosomes? by Jonny Perl, DNA Painter Blog, 12 October 2020.
- Chromosome mapping by Kelly Wheaton. Lesson 12 in the series "Beginner's Guide to Genetic Genealogy", Wheaton Surname Resources website, 2013.
- Map your chromosomes even without living grandparents. Legacy Family Tree blog, 20 January 2017.
- Chromosome maps showing centromeres, excess IBD regions and HLA region by Sue Griffith, Genealogy Junkie, 9 June 2016.
- Technique for segment triangulation when GedMatch tool not available by Sue Griffith, Genealogy Junkie, 28 August 2014.
- Chromosome mapping and GEDmatch: an overview of what they are and what the benefits are by Dan Stone, Adventures in genealogy, 30 July 2014.
- Chromosome mapping of matching DNA with adoptees by Sue Griffith, Genealogy Junkie blog, 17 April 2014.
- A second cousin adds to my chromosome map and answers a nagging genealogical question by CeCe Moore, Your Genetic Genealogist blog, 5 July 2013.
- Identifying DNA from great grandparents using second cousin comparisons by CeCe Moore, Your Genetic Genealogist blog, 25 September 2011.
Chromosome mapping tools
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:
- Kitty Cooper's chromosome mapper
- Kitty Cooper's segment mapping tool
- Mapping an ancestral couple: a backwards use of my segment mapper by Kitty Cooper, Kitty Cooper's blog, 29 August 2014.
- New compact chromosome browser on GEDmatch.
- Kitty Cooper's one-chromosome mapper A tool which allows the user to look in detail at just one chromosome. A chart can be displayed for up to 40 people who have segment matches with you on a single chromosome.
Reviews relating to Kitty Cooper's tools
- Chromosome mapping by Jody Lutter, Family History Research by Jody, 5 August 2013.
- Chromosome Mapper by Kitty Cooper – First Look by Rebekah Canada, Haplogroup blog, 4 August 2013.
Borland Genetics HIR Mapper
- 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:
- An Excel spreadsheet from Andrea Badger for maintaining chromosome maps
- Kitty Cooper's Excel file for tracking matching DNA segments
- Making a spreadsheet of autosomal DNA matches by Kitty Cooper, Kitty Cooper's blog, 15 November 2012.
- Using Chromosome Mapping to Help Trace Your Family Tree Presentation given by Tim Janzen at the Institute for Genetic Genealogy in 2014.
- Bettinger B. A small segment round up. The Genetic Genealogist, 29 December 2017.