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1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

Posted: 27 Jul 2015 5:52PM GMT
Classification: Query
It is my understanding that about 3800 DNA points are compared in order to determine if two individuals share an ancestor and if the DNA represents such sharing.

Is there a database that lists the various cM values and the cousin relationship?

What term is used to describe the "degree of ancestry" when a pedigree flows back in seven distinct paths to a unique ancestor (due to marriages of cousins) ?



Re: 1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

Posted: 27 Jul 2015 6:35PM GMT
Classification: Query
Here is a link to a chart of cm values and their corresponding relationships.

http://www.isogg.org/wiki/Autosomal_DNA_statistics

Re: 1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

Posted: 27 Jul 2015 8:39PM GMT
Classification: Query
Thanks. I had been searching for such a chart for a few months now.

I will study it and try to learn how a pedigree collapse influences the cM values.

Re: 1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

Posted: 28 Jul 2015 4:42PM GMT
Classification: Query
Pedigree collapse may generally make people appear more closely related than they are. However DNA inheritance is pretty random. That's why, except for the closest relatives, you can't use DNA to define the actual relationship.

Re: 1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

Posted: 28 Jul 2015 6:30PM GMT
Classification: Query
If a biologist were to measure the inheritance of an ancestor over six generations of his descendants, he would be able to come up with a figure to predict the possibility that the current generation carries X % of the DNA of the ancestor. If the pedigree involved pedigree collapse, the probability would be two times X %. Even if X were one part of 1024. 0.102 %

I have found some 4th cousins that match my DNA a small bit. And others who match it twice as much. I suspect that this is due to pedigree collapse.

Re: 1200 cM is close and 20 cM is distant---which cM value would indicate a first cousin?

Posted: 28 Jul 2015 7:41PM GMT
Classification: Query
Actually more likely due to the random nature of inheritance. I have a 3rd cousin who matches me at the 5th - 8th cousin level yet matches my aunt at the 2nd to 3rd cousin level. There is definitely no pedigree collapse as I've thoroughly tracked them since this is a fairly close relationship. She got more of the common DNA than would be expected and I got less.

Also some segments of DNA are "Sticky" in that they don't break up as easily so it is an all or nothing sort of thing. If you get that strong bit, you may look more closely related than you are.

Studies have been done on that and it is what they use to predict the relationships.
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