Visual phasing is a technique developed by Kathy Johnston and Randy Whited which allows to assign DNA segments of three full siblings to all of their four grandparents by comparing their crossing-over positions on a specific chromosome. (It’s even possible to reconstruct nearly complete DNA profiles of your ancestors using this technique, if you have the possibility to work with five, six or more siblings.)
WHAT ARE THE REQUIREMENTS?
- autosomal DNA raw data files of the three full siblings (or more) uploaded to GEDmatch
- multiple 2nd or 3rd cousins on several ancestral lines available for comparison
- Steven Fox’s automated Excel spreadsheet (available for download at the Visual Phasing working group on Facebook)
- advanced understanding of genetic genealogy
- analytical skills and patience
However, you can also work with two siblings and other close relatives, but it’s a lot more complicated (see examples below). And you can also work with half siblings, but you will only be able to assign DNA segments to two grandparents.
MY OWN VISUAL PHASING CASE STUDIES:
Please keep in mind that your Visual phasing results may be incorrect due to hidden recombinations. Such situations occur when two close crossovers of two siblings look like a single crossover for the third, or when very close crossovers “cancel” each other out entirely. In this case, their presence would only be suggested by additional siblings or other matches, because they won’t be visible in the GEDmatch One-to-one comparison images at all.
Here are two examples:
LINKS TO MORE CASE STUDIES:
http://thegeneticgenealogist.com/wp-content/uploads/2016/11/Visual-Phasing-Bettinger.pdf – a five part series on Visual Phasing by Blaine Bettinger
Chromosome mapping with siblings – part 1 by Ann Raymont
Chromosome mapping with siblings – part 2 by Ann Raymont
YouTube video by Lars Martin
Double Visual Phasing by Joel Hartley
Not everybody has three siblings to work with. Visual Phasing with two siblings is a lot more difficult, but not impossible, as the following examples show:
Down the DNA Rabbit Hole – Visual Phasing with Two Siblings by Deborah Sweeney
Visual Phasing with Two Siblings and a Niece/Nephew by Leanne Cooper