Browsers and Mappers

Important concepts to know for success

If you have reached this far in your initiation to Genetic Genealogy then you have read about the different types of genealogy testing available. You may know generally what each testing company offers and have briefed their FAQ section. You might, however, still be a bit fuzzy about the exact nature of when to get what test, what is it testing for and how do you go about reviewing all the matches you hope to find.

The browsers and mapper utilities mentioned here are used with AtDNA (shorthand for autosomal dna). If you have only taken a Y-dna test, for example, then these things are not useful. While both kinds of tests are testing your raw dna material they make use of different sub-sets; and, each of these different sub-sets requires using a different testing protocol and results analysis. Each sub-set of your dna material has scientific strengths and scientists have developed tests to make use of these strengths to inform us of specific results.

Understanding the scientific strengths of your different sub-sets of dna allows you to set the context of why you should be interested in a specific type of dna test and align your use of resources with what you wish to establish or prove in your genealogical time frame. For instance, the strength of testing dna from the Y chromosome allows for testing of a patrilineal biological line as every father passes almost an exact copy of the some Y dna material, starting from the beginning. While this is a great strength it is also an extreme telescopic look back on the Genome and usually requires collateral testing to help build the allied lines leading towards finding common ancestors.

When you view results in a chromosome browser several interesting things will be noted. The view which you see is an artificial composite representing the findings found in one of your 46 chromosomes and shown in 23 composite view chromosomes. Current technology for personal AtDNA testing cannot determine if the matching dna found was from 1 of 2 chromosomes inherited from your mother or from 1 of the 2 chromosomes inherited from your father.

The composite figure is drawn to resemble the outline of a typical chromosome and this sometimes leads new viewers to incorrectly assume that the small and big ends have relevance to paternal or maternal inheritance; they do not. Only matching segments matter and can determine the match quality.

Matches that testing companies find are for stretches of DNA that are half identical regions (HIRs). This is due to the fact that a relative who shares a DNA segment from a common ancestor with you can only match you along the chromosome you inherited either from your mother's side of the family or your father's side (and, of course, their respective ancestors). Thus your new relative can only match you for up to 50% (half; 1 of 2 chromosomes) DNA. Only a sibling will share a 100% fully identical regions of DNA (full; 2 of 2 chromosomes, 1 from mom, 1 from father).

As stated, a match is considered a match when a certain size or chunk of your dna matches up with another person; size matters and big is always better. The objective for the genetic genealogist is to prove that the matching segments are real or there by chance. There is technical jargon for this as follows:

Identical by descent or identity by descent (IBD) is a term used in genetic genealogy to describe a matching segment of DNA shared by two or more people that has been inherited from a recent common ancestor without any intervening recombination. The segments are considered to match if all the alleles on a paternal or maternal chromosome are identical and if the minimum threshold conditions set by the testing company have been met. Being identical by descent is contrasted to being identical by state (IBS). [ISOOG]

In other words, we must prove a match is the real deal and not just chance; we do that by a process of triangulation:

In surveying, the tracing and measurement of a series or network of triangles in order to determine the distances and relative positions of points spread over a territory or region, especially by measuring the length of one side of each triangle and deducing its angles and the length of the other two sides by observation from this baseline. [Google search]

Triangulation is a term derived from surveying to describe a method of determining the Y-STR or mitochondrial DNA ancestral haplotype using two or more known data points. The term was coined by genetic genealogist Bill Hurst in 2004. The technique is also used in autosomal DNA testing to compare matching DNA segments to determine which ancestor donated which particular segment.

If you have at least three people with the common ancestor matching on the same segment then you can infer that the segment came from that ancestor.
[ISOOG] Caution needs to be exercised as it is still possible that the match is a false positive identical by state; not the real deal and/or just by chance. This is particularly the case with small segments below 11 cMs. Triangulation is best used in autosomal DNA testing in combination with chromosome mapping. Therefore, the resources below are presented for your testing and trials.

AtDNA Browsers and Mappers

Autosomal DNA Segment Analyzer (ADSA) constructs tables that include match and segment information as well as a visual graph of overlapping segments, juxtaposed with a customized, color-coded In-Common-With (ICW) matrix that will permit you to triangulate matching segments without having to look in multiple spreadsheets or on different web pages. Additional information, such as ancestral surnames, suggested relationship ranges, and matching segments and ICWs on other chromosomes is provided by hovering over fields on the screen. You may also generate emails to persons you match from the page. The web page produced by this program does not depend on any other files and may be saved as a stand-alone .html or .htm file that will function locally or offline in your browser. You can also email the saved report as an attachment. ADSA only works with GEDmatch and the Family Finder test from Family Tree DNA.

This page was last modified: Monday, 19-Nov-2018 11:11:13 MST