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  #1  
Old 5th March 2017, 07:15 PM
JNR114 JNR114 is offline
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DNA Matches(In common with parent/child and cousins)

Can anyone answer me this?
I recently had my mother tested with ftDNA also.
Is it, or how is it, possible that a child shares more dna with many projected cousins than the parent who they are related through? The child's parents are 100 percent, certainly, not related. There are more segments shared, and Some cM on segments are even longer than the parent's..

How/why is it that so many cousins that a parent has, are not also shared with the child? When viewing matches in the parent's account, there are matches/cousins with 70 plus cM. Would you not expect to see at least some of these relatives to share some cM with that individual's child.

Can anyone shed some light and clear this up please?

Thanks.
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  #2  
Old 5th March 2017, 08:13 PM
prairielad prairielad is online now
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Quote:
Originally Posted by JNR114 View Post
Can anyone answer me this?
I recently had my mother tested with ftDNA also.
Is it, or how is it, possible that a child shares more dna with many projected cousins than the parent who they are related through? The child's parents are 100 percent, certainly, not related. There are more segments shared, and Some cM on segments are even longer than the parent's..
Each position tested has two values a maternal value and a paternal value. We have two of each chromosome, one of each from mother, one of each from father. 46 Single Chromosomes, 23 pairs.

There are only four values (Bases) that make up DNA
A, C, G and T.

So each person for each position will be either AA, CC, GG, TT, AC, AG, AT, CG, CT , or GT.

Algorithm looks for a matching sequence of single letters all in a row between you and match.
False matching may occur at the beginning and end of segment due to this. Picking value from your maternal then your paternal. Same with match's maternal and paternal values.
Depending on size difference between match with parent and match with child, this is probably the reason, false matching at the beginning and end of segment.
One would have to phase results to confirm and compare (ie at Gedmatch)
Quote:
Originally Posted by JNR114 View Post
How/why is it that so many cousins that a parent has, are not also shared with the child? When viewing matches in the parent's account, there are matches/cousins with 70 plus cM. Would you not expect to see at least some of these relatives to share some cM with that individual's child.

Can anyone shed some light and clear this up please?

Thanks.
This depends on whether not you inherited that same segment from parent. You only inherit a random 50% of each parent.

Match may be on parents paternal chromosome, but for that segment you inherited that parents maternal chromosome.

Parents pairs randomly swap sections of varying lengths to form the single chromosomes passed onto you from that parent. It all depends on whether or not you inherited that maternal or paternal chromosome segment from parent where this match is located.

Last edited by prairielad; 5th March 2017 at 08:18 PM.
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  #3  
Old 6th March 2017, 06:27 AM
Dabney Carr Dabney Carr is offline
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Did your mother submit a test kit to FTDNA or was she tested elsewhere and you did you do an autosomal transfer?
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  #4  
Old 6th March 2017, 08:43 AM
high734 high734 is offline
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So for this example there are four people: Mom, Dad, Child and Cousin.
1) Child shares more DNA with Cousin than Mom
2) Dad and Mom are 100% not related

How?
I'm picking arbitrary ancestors for this example. Let's say that Cousin has Great Great Great Grandparents in common with Mom. And they share the correct amount of DNA for this relationship and the Child inherited either all or less of the same DNA. But the Child has more DNA in common with the cousin that must have come from the Dad. Right now you are saying but Mom and Dad are not related, and this could be true(and is true for this next part). Dad could share one of the other sets of Cousin's Great Great Great Grandparents (there are more than one!) and all of the others would not be related to Mom.
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  #5  
Old 12th March 2017, 04:31 PM
JNR114 JNR114 is offline
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I had my mother test with Ancestry.com and then transferred the data to ftDNA.

I do see the possibility that a distant, older, cousin from my mother's side could had certainly got with another distant cousin from my father's side. This would create more shared segments than my mother. This would explain the additional segments shared, more than the mother has. But, I am still having a hard time seeing, for the segments shared with my mother, I share longer segments(more cM)on just one segment than my mother with a cousin. Unless the father's cousin's segment just happens to line up just perfectly where the mother's segment began or ended.? What are the odds? I suppose too, that the "False matching" glitches explanation, or whatever they are, could explain this also.
I did transfer both kits to gedcom. I am seeing the same thing there, but with numerous cousins.

Another question within ftDNA, why would I only share 153 total cousins with my mother when utilizing the "in common with" search tool, out a total of 1317 cousins.
When I log into my mother's account, she has many more cousins than my total even.. ???


Also, is it possible to receive genes/sequences from a grandparent, of the mother's parents, that the mother somehow did not get and skipped a generation?

Last edited by JNR114; 12th March 2017 at 04:45 PM.
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  #6  
Old 12th March 2017, 04:47 PM
JNR114 JNR114 is offline
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I had my mother test with Ancestry.com and then transferred the data to ftDNA. It's been a while, but I believe I had tested with both, due to incompatible transfer files at the time.

The statement in the previous post about my mother having more cousins than me was incorrect. My mother's account has only 300 matches, as opposed to my total of 1317. Of those 300, I only match/share 153 of those.

Last edited by JNR114; 12th March 2017 at 05:01 PM.
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  #7  
Old 12th March 2017, 07:11 PM
Lucky Lucky is offline
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Your last post is making the situation more clear. When you transfer from Ancestry you only get the DNA matches out as far as 3rd-5th if it is a recent Ancestry test.

If you tested with FTDNA or took the earlier version of the Ancestry test then you would have your cousins to 3rd-5th and also your speculative cousins. As FTDNA can tell your DNA with a lot more accuaracy past 3rd-5th cousin, all of your DNA is showing up.

In your mother's case not all the smaller segments can be tracked hence why she would appear to have a smaller match than you when in fact that isn't the case, FTDNA are just being more cautious in your mother's matches as its a transfer kit. They can't provide the more speculative matches (and potentially add extra cMs to the existing blocks shown) unless you upgrade the test with them. It costs $59 and requires a sample to be provided.
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  #8  
Old 19th March 2017, 03:16 PM
cmbearly cmbearly is offline
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Regarding the first question, is that due to the cause of recombination - ?
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  #9  
Old 20th March 2017, 09:12 AM
cmbearly cmbearly is offline
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So could this same type of situation occur with half siblings?
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