I love logic puzzles and DNA is definitely full of logical puzzles. After reviewing DNA recombinations from my own project, I have developed a chart that helps me understand my grandparent’s DNA through Visual Phasing.
Visual Phasing is an advanced technique for genetic genealogists where the results from siblings, can be used to determine part of the genetic makeup of grandparents. This technique was developed separately by Kathy Johnston and Randy Whited around 2015.
There is a Visual Phasing Working Group on Facebook that is run by Blaine Bettinger if you want to learn more specifics about the technique.
1. You need the DNA results of at least 3 full siblings.
If you only have 2 siblings or if you have 2 full siblings and a half-sibling it is a lot more difficult. From these siblings, you are mapping out where recombination points happened.
2. Go through and assign segments to generic grandparents, as far as possible.
3. Use other close relative matches to refine these assigned segments into maternal or paternal chromosomes.
4. As you identify matches with more distant relatives, these maternal and paternal segments can be assigned to specific grandparents.
Sounds simple, right?
Well, it is not.
In a lot of cases, the logic puzzle of each chromosome can’t be solved because there are multiple solutions. In other cases, there aren’t enough close relatives to effectively assign paternal and maternal matches. Finally, if you don’t know the relationship clue for distant relatives, it can be very difficult to assign segments to a grandparent.
Through the Family History Fanatics Recombination Project, (which you may have seen on the sidebar or on the bottom of your mobile screen), I have been gathering data on grandparent/grandchild pairs and the recombinations that happen between them. You can still contribute to the Recombination Project using the LINK HERE.
As I was going over some of that data I realized that I have something that can help in Visual Phasing. Because maternal and paternal chromosomes recombine at different rates, we can expect specific chromosomes with a certain number of segments to be maternal or paternal.
I have created this chart to help you sort your matches.
|Download the full copy of this chart HERE.|
As you’ll see in this chart, there is only one chromosome/segment combination that is definitely Paternal, that is any chromosome 1 that did not have a recombination.
There is a bunch of definitely Maternal chromosome/segment combination, mainly when there are 4 or more segments. These definite chromosome/segment combinations are because there are no contrary examples in the crowdsourced data I have.
- Likely combinations have a 90% or greater chance of being correct.
- Probable combinations have between a 60 and 90% chance of being correct.
- The No Data cells indicate that the crowdsourced data hasn’t found any examples of this. So if you come up with this combination, either:
- the grandparent has a unique combination that I haven’t seen yet, or
- there is a mistake in your visual phasing.
As more crowdsourced data is added to the database, I’ll be able to revise this chart.
Watch this video so I can show you a couple of examples of how to phase my DNA results. It’s a bit easier to show in video than in words.
It should be noted that you aren’t going to resolve all of your chromosomes with this chart. If you have close cousins with known relationships, then that will give you more accurate results.
Without any other information, for at least a handful of chromosomes, this chart can help you get from generic grandparents to the paternal/maternal assignment stage. That narrows down the potential relatives to research or matches.
If you have done some visual phasing, see if this chart can help you progress some of the logic problems a step further. If you have further questions, add them below.