First Name:  Last Name: 
[Advanced Search]  [Surnames]

Smith Official DNA & One Name Study Project
Smith DNA Official Project-All Locations-A FamilyTreeDNA Project

Come Join the Smith Official DNA Project at FamilyTreeDNA with a DNA Kit!


  Guestbook ALL Posts  Get a Gravatar pic for post           Login Guestbook

Autosomal Chromosome Mapping Explanation

Here's a chart we have done for the Smith DNA project showing the percentages of autosomal matching among generations.

from ISOGG

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.

Mapping specific DNA segments to early ancestors is more challenging, particularly in endogamous (inter-married) populations. In such situations it is helpful to use a complementary technique known as triangulation. This involves finding other distant cousins who share the same segment and who share the same common ancestor. The caveat is that without chromosome mapping you cannot be sure that the documented common ancestor is the one who provided the shared DNA segment. The more matches who share both a specific DNA segment and a specific ancestor with you, the higher the probability that the DNA segment came from the common ancestor.

One should be particularly cautious about mapping segments to people who are related to you at no closer than about the 6th cousin level without additional corroborating evidence, such as two or more people who share the same segment with you (or your parents) and who also share the same common ancestor.

(6/4/2014 Views 1146)


Good link from ISOGG to show the simple mathematical average of sharing for autosomal.


Add a Reply

For the Smith Official DNA Project (All Locations) a minimum of 25, or better, 37 YDNA markers, is strongly recommended. Many times one can appear to match other kits but the match falls apart after 12 markers. We do not attempt to match kits into groups on less than 25 with the exception of a strong paper trail or known family kinship with another tester.


Smith Official DNA Project (All Locations)  data is copyrighted, in aggregate,  to this project, a FamilyTreeDNA Project
Any other aggregate use is not permitted, without the expression permission of the administrators of this project.
We appreciate links to the Smiths Official DNA -All Locations project, but do ask that site links, particularly when there is potential confusion, point to the
Join page at FamilyTreeDNA for the Smith Official All DNA Project, that you clearly indicate that the link goes to the Smith Official DNA  Project (All Locations)  and that our project data not be sent out via spreadsheet, email or other means without our (admins on the Smith Official DNA Project) express permission.  The Smith Official DNA Project at FamilyTreeDNA is not affiliated with strictly regional projects Smith Connections-Northeastern which is a FamilyTree regional project for those with connections in specific northeastern US states such as NY/CT, etc  nor with Smiths of Abbeville SC,. We are the official Smith DNA project for ALL Smith Schmidt Smyth Smythe etc of ALL Locations and include all northeastern US states as well as Abbeville SC Smiths and all other locations in the world. Thank you.