Methods of analyzing chromosomes matches - help needed!

[Elena Govor]

I would appreciate some advice about analyzing FF test results.

I have test results of my husband Vladimir and his 2nd cousin Eugeny. They have common paternal great grandparents Raphael and Liba who lived in mid-nineteenth century. On chromosome 8 Vladimir and Eugeny have matching segment 24 cM.

I just ponder what does this 24 cM segment means in respect to their great grandparents? Does it mean that either their great grandfather or their great grandmother had the same segment of chromosome? Or that this segment appeared only when chromosome halves of Raphael and Liba combined when their sons (grandparents of Vladimir and Eugeny) were born?

The second set of questions is connected with further analysis of their matches. Vladimir has over 20 matches (5-20 cM) on chromosome 8 within the start and end location of his 24 cM match with Eugeny. I have checked if Vladimir's matches appear in Eugeny's chromosome browser results and discovered that nearly half of people whom Vladimir matches on chr. 8 do not appear among Eugeny's matches. Some present as Eugeny's cousins, but do not have match on chromosome 8 with Eugeny.

But some people do appear among Eugeny's matches. For instance Howard shares about 20 cM with Vladimir and with Eugeny at the same section of chromosome 8, which Eugeny shares with Vladimir. I guess this means that Vladimir, Eugeny and Howard have a common ancestor.

Thus Vladimir has two groups of matches on the same 24 cM section of chromosome 8 - some he shares with Eugeny, some does not. Is it correct to consider that the first group will be related to their great grandparents Raphail and Liba, while the second group might be from Vladimir's other great grandparents? But the question is - which one? If Vladimir received half of the section in chr. 8 from Raphail and Liba via their son Michael, does it mean that the other half of the same section of chr. 8 must have have come from Michael's wife side? Or it equally could come from Vladimir's maternal great grandparents? If there is an answer to this question it would help untangling relationships very much.

And the last question. On the same section of chromosome 8 T* has a match with Vladimir 7 cM and match with Eugeny 1.8 cM. Does this tiny match with Eugeny means that T* belongs to group that matches Vladimir and Eugeny and their ancestry via Raphael & Liba? Does it definitely mean that T* cannot belong to the second group that matches Vladimir only on chr. 8?

I will be very grateful for your help.

[mkdexter]

I would appreciate some advice about analyzing FF test results.

I have test results of my husband Vladimir and his 2nd cousin Eugeny. They have common paternal great grandparents Raphael and Liba who lived in mid-nineteenth century. On chromosome 8 Vladimir and Eugeny have matching segment 24 cM.

I just ponder what does this 24 cM segment means in respect to their great grandparents? Does it mean that either their great grandfather or their great grandmother had the same segment of chromosome? Or that this segment appeared only when chromosome halves of Raphael and Liba combined when their sons (grandparents of Vladimir and Eugeny) were born?

Yes the 24 cm segment that Vladimir and Eugeny share came from their great grandparents Raphael and Liba. Everything Vladimir and Eugeny share on the chromosome map would have come from Raphael and Liba.

Raphael and Liba would have the same segment plus all the rest which didn't get passed down over time to the descendants, Vladimir and Eugeny. Remember the other DNA in Vladimir and Eugeny came from all their other great grandparents too - so only a certain amount comes from Raphael and Liba and that is the amount you see in the FF test.

[mkdexter]

The second set of questions is connected with further analysis of their matches. Vladimir has over 20 matches (5-20 cM) on chromosome 8 within the start and end location of his 24 cM match with Eugeny. I have checked if Vladimir's matches appear in Eugeny's chromosome browser results and discovered that nearly half of people whom Vladimir matches on chr. 8 do not appear among Eugeny's matches. Some present as Eugeny's cousins, but do not have match on chromosome 8 with Eugeny.

This is not going to be conclusive. Maybe these other matches are related to Vladimir's mother and not father. If they don't match Eugeny who is related to Vladimir's father then wouldn't it be possible they match Vladimir's mother instead? Either way the results alone are not conclusive, you would need more data to confirm your theory as to who they are related to.

But some people do appear among Eugeny's matches. For instance Howard shares about 20 cM with Vladimir and with Eugeny at the same section of chromosome 8, which Eugeny shares with Vladimir. I guess this means that Vladimir, Eugeny and Howard have a common ancestor.

Yes this is probably true.

Thus Vladimir has two groups of matches on the same 24 cM section of chromosome 8 - some he shares with Eugeny, some does not. Is it correct to consider that the first group will be related to their great grandparents Raphail and Liba, while the second group might be from Vladimir's other great grandparents? But the question is - which one? If Vladimir received half of the section in chr. 8 from Raphail and Liba via their son Michael, does it mean that the other half of the same section of chr. 8 must have have come from Michael's wife side? Or it equally could come from Vladimir's maternal great grandparents? If there is an answer to this question it would help untangling relationships very much.

Because the test can't figure out what is maternal and paternal and you have to use your list of matches and compare to known relatives, you can't figure out which is maternal and paternal by the map alone. The FF chromosome browser will show you either a paternal segment or a maternal segment all on the same page You could have a full overlap of person A and person B to Vladimir across the entire chromosome map, the whole thing, and yet A be maternal and B be paternal related to Vladimir. For example a mother to child covers the entire map, and a father to the same child covers the same area. If you look at the two parents on the same map of the child you won't be able to see which one is paternal or maternal, in fact they will both cover the same exact area on their child's map. You have to know that by other facts, lists, trees, etc., what segment is maternal and what segment is paternal. Look at my next reply for an example of chromosome 8.

And the last question. On the same section of chromosome 8 T* has a match with Vladimir 7 cM and match with Eugeny 1.8 cM. Does this tiny match with Eugeny means that T* belongs to group that matches Vladimir and Eugeny and their ancestry via Raphael & Liba? Does it definitely mean that T* cannot belong to the second group that matches Vladimir only on chr. 8?

I will be very grateful for your help.

No it doesn't mean that. FF only bases a match on the largest segment between two people. All the other smaller segments are either population noise, or very distant overlaps, or something from many generations prior to the actual common ancestor. I have these same small segments from people related to my father on the matches I have who are related to my mother. In other words they can be anything.

[mkdexter]

paternal and maternal segments on map

A person can have both a paternal and maternal match show up at the same place on the chromosome map. Here's an example. The orange is this person's father and the blue is this person's mother.

This is why you need more information about the match to figure out if the overlapping segments are a paternal or maternal connection.



By the way, orange does not mean paternal, it just happens to be the color that is used for choice number 1.

MD.

[mkdexter]

is green related to orange or blue?

Better yet.. this should make a point.

Who is Green related to? Orange or Blue?

Remember in this specific example Orange is Father and Blue is mother.



The point is you can't tell just by looking at the map. Look at the match lists too. It happens that Green is only related to Orange, not Blue. You would have never known this by looking at the map. What you see here are two paternal segments and a maternal segment.

[Elena Govor]

Dear Matt,

This was very helpful, thank you very much!

Elena

[vivianruth]

Follow-up question

I have an additional question for Matt regarding his comments on Elena's question:

What if the great-grandparents were, themselves, cousins to some of Vladmir's other great grandparents? I have this in my family, and I think it really muddies the waters.

Vivian

[mkdexter]

I have an additional question for Matt regarding his comments on Elena's question:

What if the great-grandparents were, themselves, cousins to some of Vladmir's other great grandparents? I have this in my family, and I think it really muddies the waters.

Vivian

Yes it will. This is more notable when ancestors share segments to both the maternal and paternal lineages.

I have a predicted 3rd cousin, who is predicted as a 4th cousin to my mother. The extra shared segments from my paternal side fooled the algorithm.

If this issue of being interrelated occurs too much then it results in higher than expected sums and/or compound segments and either of those affect the algorithm's predictions.

This would be difficult to find unless a parent, aunt or uncle also tested and you were to notice the differences between the two people a generation apart who both match the same 3rd party.

MD.