Visual Phasing is a process by which the DNA of three siblings is assigned to each of their four grandparents using identified recombination points, without requiring the testing of either the parents or grandparents. Although the process does not automatically reveal which segment belongs to which of the four grandparents, matching with cousins provides this identification as a further step of the process.
I know some of my readers may be asking: what are you talking about? If you know you are genetically related to me, please read on!
The step-by-step on how to do visual phasing starts at Visual Phasing: Part 1 at his blog. (There are five parts.) He also includes links to visual phasing work of other genetic genealogists.
Since I have two siblings and we all have our DNA at GEDmatch, I decided that I wanted to try this. What I want to do here is to show why it's helpful to me if known relatives test their DNA, AND upload the raw data to GEDmatch.com.
The images below include screenshots of "One-to-One" DNA chromosome browser comparisons from GEDmatch between me and brother S, between me and brother R, and between R and S.
Where you see solid green section, that means the two chromosomes (one from dad and one from mom) are fully-identical between those siblings. Where you see yellow (and green), that means that the siblings match on one of the two chromosomes. This is half-identical sharing. The red sections indicate that the siblings don't match on their pair of chromosomes.
I have added the vertical lines to represent recombination points in the DNA of my mother or my father as the DNA was passed down to me and my brothers.
At the bottom of the image is where I actually map the chromosome to my grandparents, using blue and red for my maternal grandparents and green and purple for my paternal grandparents.
Taking the suggestion from Blaine, I started with the X-chromosome. Daughters receive two X chromosomes, one from dad and one from mom. Sons receive one X chromosome, from mom (because they get the Y chromosome from dad). That's why in this example, only I (represented by E) have the long green bar below the blue and red bars. The green bar represents the X chromosome that I received from my dad. Brothers R and S only received one X chromosome - from mom.
Because Blaine does a good job of explaining the step-by-step of how to use this method, I'm not going to go through all those steps, but I can tell you that a cousin of my mother's shares DNA with brother R from 2,700,000 to 22,600,000 (numbers are rounded). Because I know that this cousin descends from Lowell Copeland and Ethel May Greeley (my mother's paternal grandparents), I know that the red segments represent DNA that came from the Copeland/Greeley ancestral line (i.e. my maternal grandfather). Therefore the blue segments represent DNA that came from the Hunter/Lysle ancestral line (i.e. my maternal grandmother).
Following is another example, using chromosome 19.
In this case, I was able to match the maternal (Copeland/Greeley) cousin to just E, so red represents DNA from my maternal grandfather (Copeland/Greeley ancestry) and blue represents DNA from my maternal grandmother (Hunter/Lysle ancestry). In this case, on this chromosome, my grandmother Hunter's DNA passed down to my mother without recombining with my grandfather Copeland so both my brothers have just the one blue segment. Only E received Copeland/Greeley DNA on this chromosome.
I was able to match a paternal second cousin to me and brother S before location 8,600,000 (rounded), so I know that the purple segment represents DNA that came from my paternal grandfather (Pyle/McAlpin ancestry) and therefore the green segments represent DNA that came from my maternal grandmother (Adsit/Ashby ancestry).
Because of the nature of the family of my paternal grandmother (Elizabeth Adsit, 1897-1983), I don't have known first cousins, second cousins or third cousins on that line.
These examples of visual phasing represent just two of the 23 chromosomes that I hope to ultimately map to each of my grandparents. These are relatively short chromosomes, making them a little easier to work with.
Many of the chromosomes are much longer and have many more recombination points and it gets very confusing, especially when I can't find any match between my few known relatives at GEDmatch and the three of us. When the relation is further away, less DNA is shared so it's helpful for me if more known second cousins test and upload their DNA to GEDmatch.
Ultimately, this will help me when I am trying to determine how I am related to an unknown genetic match by narrowing down which grandparent's ancestry I need to look at more closely for a common ancestor.
I thank those who have tested and have let me upload their results to GEDmatch: a maternal aunt and first cousin, a first cousin of my mother, a paternal second cousin and a paternal second cousin once removed.
To my known relatives: if I can help you help me with my Visual Phasing project by testing, or by uploading your raw data to GEDmatch, please feel free to contact me at elizhandler -at- gmail.com.