Segment Matches with Grandparents Using Crossover Lines

[Kathy Johnston]

Many have asked for some suggestions for strategies used in the visual phasing of grandparents when parents are deceased. I put together a step-by-step PDF file from a PowerPoint presentation. It utilizes crossover points derived from comparisons through GEDmatch. I can explain each step once the slides load. I have permission from this family to discuss the results. The ultimate goal is to show matching between siblings and each set of grandparents for one chromosome.

[Kathy Johnston]

Originally Posted by Kathy Johnston

Many have asked for some suggestions for strategies used in the visual phasing of grandparents when parents are deceased. I put together a step-by-step PDF file from a PowerPoint presentation. It utilizes crossover points derived from comparisons through GEDmatch. I can explain each step once the slides load. I have permission from this family to discuss the results. The ultimate goal is to show matching between siblings and each set of grandparents for one chromosome.

Here are the instructions that go with the slides. I wasn't sure I could get it all in one upload. I guess it is really the phasing of siblings (not the grandparents) to determine the segments that came from each of the grandparents. It is basically just triangulating your segments back to your grandparents by using sibling matches. I have found it to be quite useful. Suggestions are welcome.

[Canyon Wolf]

Kathy, once again you have been extremely helpful with my understanding of phasing.

[Bob Hesse]

I will soon have the results back from my four full siblings to add to mine, giving me an excellent opportunity to try out this process.

I have a couple of questions, though. Each chromosome has two halves, but GEDmatch supplies only a single line of commonality. Consider the simplest situation, where siblings A and B match one side of a chromosome exactly, and they have one break-point on the other side. Will GEDmatch show that they match 100% on the entire chromosome, or will the break-point be visible? If the break-point is visible, how would I know that the opposite side is a complete match?

[Frederator]

Originally Posted by Bob Hesse

I will soon have the results back from my four full siblings to add to mine, giving me an excellent opportunity to try out this process.

I have a couple of questions, though. Each chromosome has two halves, but GEDmatch supplies only a single line of commonality. Consider the simplest situation, where siblings A and B match one side of a chromosome exactly, and they have one break-point on the other side. Will GEDmatch show that they match 100% on the entire chromosome, or will the break-point be visible? If the break-point is visible, how would I know that the opposite side is a complete match?

Gedmatch will show the break as a half identical match--a narrow yellow stripe--in a field of green, fully identical matching SNPs under the graphical display option.