Inferred Chromosome Mapping using DNA Painter

A new tool has been added at DNA Painter: the Inferred Segments Generator. If you have a parent, sibling, half sibling or a descendant of a sibling whose DNA test results are on any of the sites displaying the chromosome browser, then you can make use of this new tool. Just a note though that it won’t be of use to you if your grandparents are related, or if they’re from a group with a high level of endogamy: you have to have grandparents whose lines are clearly distinct.

If you have no idea what a chromosome browser is, take a look at my previous post [here]. What you need to understand for inferred chromosome mapping is that we have two copies of each chromosome: the copy we inherited from our father and the other from our mother. DNA Painter is all about helping us to separate out which of those two copies any specific DNA match segment should sit on. However, homing in on any one of those copies, the DNA on either the mother’s or father’s copy is a random mix of what they inherited from their own mother and father, and this is why we talk about ‘segments’ – we will have a ‘chunk’ of DNA from our father that came from his own father’s side, followed by another chunk from his mother’s side, and so on. So at any specific place on our two copies (maternal and paternal) of any specific chromosome, we have inherited DNA from either our grandmother or our grandfather. A DNA match means we have inherited exactly the same segment as our DNA cousin, but precisely where the segment match begins and where it ends is where one of us – me or my DNA cousin – has switched at that point in our DNA inheritance from one grandparent to the other.

Inferred chromosome mapping is simply about using this understanding alongside our DNA results in comparison with those of our parent, sibling or nephew/niece. Let’s say my brother and I both match second cousin A on our maternal line. We know that this shared DNA comes from our mother’s paternal line. Now let’s say my brother’s shared segment with second cousin A on one segment is longer than mine. We can infer that here, the DNA I inherited from our mother has switched from my maternal grandfather to my maternal grandmother. Now, when I get a new match on those segments that I have been able to allocate through ‘inferred mapping’ to my maternal grandmother, it greatly reduces the parts of my tree I have to look at in my efforts to locate any new matches.

In the short video below, Jonny Perl, founder and creator of DNA Painter, explains all of the above with diagrams. He then explains what his new Inferred Segments Generator is and how you can use it for inferred chromosome mapping. I’ve been able to use it so far for just two matches my brother and I share – a second cousin and a second cousin once removed (both on the same line) – and I’ve been able to ‘infer’ and allocate 195 centiMorgans worth of segments.

For those of you who are into DNA for genealogy – may you be blessed with many, many centiMorgans of inferred DNA!

*****

For the next three months I have a very heavy workload and will be reducing my posts to one per month, the 1st of July, August and September. From October I’ll be returning to my usual pattern of two posts per month. Until next time, have a good June.

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