Maths and Science Applied to Genetic Genealogy


Use the # of segments in your relationship predictions!

The most amazing thing has come to genetic genealogy! You can now enter your # of segments along with total cMs into SegcM to get far better predictions than anyone’s ever seen.

Add a sibling to a new version of SegcM to improve your predictions

You can now get predictions for you and a sibling to an unknown DNA match using SegcM for Multiple Testers.

Please submit to the new DNA match survey

This DNA match survey is helping to develop better tools for genetic genealogy. It has already been used to implement genotyping errors into SegcM for Multiple Testers. This survey is different in multiple ways: comprehensive data collection, scientific design, validated data, and you can request to see your prior submissions.

The first and only scientific paper on relationship predictions

In 2016 AncestryDNA did simulations so they could start providing relationship predictions. That’s all that was available to third party tools for the next few years. Read about how far we’ve come since then.

Relationship predictions from Ped-sim!

The first ever relationship prediction tools from a peer-reviewed data source are here. One is a traditional relationship prediction tool and another is for known or suspected double cousin relationships. More recently, a percentage input box has been added, which makes the Orogen predictions the first ever to include X-DNA (for 23andMe data).

GEDmatch incorporates the relationship predictor from!

You can read here about how GEDmatch is now using DNA-Sci relationship prediction probabilities on its One-to-Many tool.

A three-part series on using the kits of multiple tested relatives

Almost everyone who has siblings tested and used them in a WATO tree was doing that wrong until recently. I explore several methods and find that the best methods are ones that approximate the amount of a parent’s DNA that the children have, when combined:

Part 1: The Theory

Part 2: Testing the Methods

Part 3: Empirical Data

The first ranges of X Chromosome DNA

If you’re interested in X Chromosome DNA, be sure to check in with this article from time-to-time as I update it with data for additional relationships. This is the only place to find shared X-DNA ranges. Data for great-aunts/uncles, half-great-aunts/uncles, and 2nd cousins once removed are now available.



You can now get relationship predictions from the # of segments and total cMs. It works much better than expected. The data come from a peer-reviewed source. Other predictors use simulated data from 2016 or earlier.


This tool is similar to the above relationship predictor except that it includes 3/4 siblings, double 1st cousins, and many other double cousin relationships. You can’t find these in any other relationship predictors.

segcm for two siblings

You can now get improved relationship predictions by entering the amount of DNA you and a sibling share with an unknown match.

AYPR/ROH Predictor

After using the GEDmatch “Are Your Parents Related?” tool, the best thing to do next is to enter the cM amount directly into this tool.


How much of an ancestor’s DNA do you have? How much would you be able to reproduce if you and various relatives all had your DNA tested?


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