I have seen in the examination of family trees where individuals sharing a great grand parent marry and have children, somewhat commonly in pre-American Civil War, which I would think would create some interesting confusion when examining Autosomal DNA (atDNA) results?
I have reviewed ISOGG's Autosomal DNA results chart on what to expect, and reviewed the prior questions "Generational Loss with DNA testing" & "Working with Autosomal DNA results" but they do not address this or other close relationships (both illegal and taboo) on how that might look in an autosomal DNA result, knowing how this might 'look like' would be interesting reference information.
I will also first caveat that I realize that I am aware that more distant relationships will also influence shared cM results such as if you happen to share a relative 5 generations back and didn't know it. In this case I am looking for clarification on what the 'starting number' should be so I can use this for exploring theories about distant relationships as well as for 'orphan' situations.
Question: Has anyone seen a chart (or can produce one or explain) of how the following relationship's offspring would look like with a Autosomal DNA to a common individual?
Such Would you split the difference or still use the 50% rule to have the expected number of shared cMs?
- 2nd Cousins having a child
- 1st Cousins having a child
- Uncle/Aunt & Niece/Nephew having a child
- Brother & Sister having a child
- Parent & Child, having a child
In perhaps the easiest example the incest relationship of parent and child; assuming the child had the 3400 cMs of the involved parent (~50%) would their resulting child be higher than 3400 cMs of the involved parent or does other math come into play and by how much?
I am primarily looking for Autosomal shared cMs at this time vs. Autosomal and X, but if you can provide an explanation of X too great.