What are benefits of getting a cousin to do the y-DNA testing along with you?

[dwight]

My question is how much might be learnable by getting my one and only patrilineal 2nd cousin to do the y-DNA test?

If it turns out my 2nd cousin and I are, say, 66/67 matches, is there any way to backwards predict what our GGF's values were?

Is my assumption correct that if it turns out my 2nd cousin and I are exact 67/67 matches, that it would be reasonable to conclude that our GGF had the same Y67 values? (I suppose a marker could mutate from 11 to 12 and then back to 11? in which case my assumption would have been incorrect)

Would knowing whether my cousin and I are, say 67/67 matches vs., say, 64/67 matches help in evaluating other matches I have, and assessing our generational distance? In other words, would seeing no mutation in these 3 generations vs seeing changes in several allele values in these 3 generations tell us anything about how close or distantly related other matches are to us?

My research interest is in learning something - anything - about my great grandfather. He said he immigrated from Denmark in 1860, he married and had kids (including my grandfather) in Illinois, but we know nothing about whether he had siblings or not, and nothing about his parents other than on one Census form it says they were born in Denmark too.

I have my test results up to Y37, and will now patiently await my Y67 results. I have a 34/37 match and two 24/25 matches, only one of whom (and he lives in Norway - the other two are in the US) has responded to my emails.

As always, many thanks to those of you who take the time, interest, and effort to respond! It's very much appreciated.

Dwight

[Jim Barrett]

I have been able to get 12 "cousins" to test. We have learned that one wasn't a cousin. His genetic distance was greater than the number of markers he had tested. We have two cases where we have shown that the adoptive father was not the also the birth father.

This leaves us with about 9 "cousin" who have tested from 12 to 67 markers. Most of these people are at least second or third cousins from each other and as much as fifth cousins. I believe buy taking the "average" we have a general idea of the Haplotype of out common ancestor who would be my 4th great grandfather and the 6th great grandfather of one of the members. I do not believe we know exactly what his Haplotype was. Maybe we do for the first 12 markers but not much beyond that.

You didn't mention what you would learn if your results came back matching only 30 out of 67. That is about what happened with the first "cousin" who tested after me. The question then became which one of us, if either of us, had the true family Haplotype. This "cousin" and I had been sharing data for years before e-mail, DNA testing or the Internet. Without the DNA test we would have never known there was an error in our data.

[dwight]

Jim, your point here gets at a question I've been trying to make sense of. Is there something substantively and hierarchically different about the 4 panels of markers (12, 13-25, 26-37, 38-67)? (Or, are they just arbitrary groupings of markers).

I assume there is something to the how and why of the groupings - else why would 0 be set as the genetic distance bar for 12 markers, but higher numbers for the others.


[QUOTE=Jim Barrett;257623]I believe buy taking the "average" we have a general idea of the Haplotype of out common ancestor who would be my 4th great grandfather and the 6th great grandfather of one of the members. I do not believe we know exactly what his Haplotype was. Maybe we do for the first 12 markers but not much beyond that.

[mkdexter]

Jim, your point here gets at a question I've been trying to make sense of. Is there something substantively and hierarchically different about the 4 panels of markers (12, 13-25, 26-37, 38-67)? (Or, are they just arbitrary groupings of markers).

It is based on the processes in the lab. Certain chemicals (primers, etc.) are made for certain panels.

I assume there is something to the how and why of the groupings - else why would 0 be set as the genetic distance bar for 12 markers, but higher numbers for the others.

It is the accumulated number of markers that allows the genetic distance tolerance to change:

markers 1 - 12 = reports if genetic distance is 0 - 1*
markers 1 - 25 = reports if genetic distance is 0 - 2
markers 1 - 37 = reports if genetic distance is 0 - 4
markers 1 - 67 = reports if genetic distance is 0 - 7

You can see this sometimes whenever someone has a genetic distance of 2 in the first panel because they will not show up as a match but once more panels are tested that match appears since the genetic distance tolerance is wider at more markers.

* optional

[Jim Barrett]

Dwight, I believe Matt took care of your questions.

[dwight]

Indeed, he did. But just to be absolutely clear, I want to confirm one thing: the genetic distance calculations are *cumulative*: So if you are 11/12 in the first panel and 12/13 in the second panel, your GD at 25 markers is reported as 2 (assuming that the change on each marker is 1 and not a higher value). In other words the -1 or -2 reported at 25 markers is cumulative for all 25 markers, not just for the second panel of 13-25. Am I right? Thanks, again!

Dwight, I believe Matt took care of your questions.

[MMaddi]

Indeed, he did. But just to be absolutely clear, I want to confirm one thing: the genetic distance calculations are *cumulative*: So if you are 11/12 in the first panel and 12/13 in the second panel, your GD at 25 markers is reported as 2 (assuming that the change on each marker is 1 and not a higher value). In other words the -1 or -2 reported at 25 markers is cumulative for all 25 markers, not just for the second panel of 13-25. Am I right? Thanks, again!

Yes, the results for the higher panels (13-25, 26-37, 38-67) are cumulative. They include the mismatches from the previous panels and any mismatch in the highest level panel.

[Jim Barrett]

Dwight,

Genetic distance will be the sum of the differences between the reported values OR LESS. The rules change for multi copy markers. It does not matter how many markers you are looking at. Of course the number of markers is very important.

A genetic distance of 5 over 67 markers is a much closer match than a genetic distance of 5 over 25 markers. It would be possible for the genetic distance of 5 over 25 markers to be genetic distance of 5 over 67 markers if there were no new differences in the additional markers.

[T E Peterman]

The main value is triangulation. If two 2nd cousins test & match 67/67, it would be reasonable to assume that the MRCA (in this case, your great grandfather) had the very same markers.

To be scientifically sound, a person can't just test himself and declare that his results are those of his patrilineal great-great-great grandfather. But if you test a patrilineal cousin & the two of you match, then you are on safe grounds representing those markers to be those of your MRCA.

Timothy Peterman