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  #11  
Old 17th February 2018, 02:17 PM
clintonslayton76 clintonslayton76 is offline
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FTDNA cannot describe an anomalous relationship, period. I do not understand why you are asking a speculative question about results that we cannot see. Because I do not have access to algorithms used by FTDNA to determine if a 1900 CM share is biased toward 1) Full Siblings or 2) Grandparent/grandchild, aunt-or-uncle/niece-or-nephew, half-siblings, wondering about it seems pointless unless such shares have been seen on FTDNA.

The important value is the cM share, not any WORDs attempting to categorize a result. There is nothing authoritative about DNA estimations of either origins or relationships, but interpretations of results so far have resulted in various (conflicting) origin theories and tables (ISOGG as an example) where you will see the normal possibilities. A population where endogamy is the cultural norm would no doubt show more vague estimations if it develops its own tables. And IV fertilization will continue to challenge "norms."

The highest share can only be for a parent or twin with no accounting for suspected incest. Much of the world's couples are closely related, but not that closely related. If someone is sharing enough with a grandfather to make the gf look like a parent, he will show as a parent even if another male person shows as a parent. The share estimations are not concerned with mimicing a family tree, they are simply translated into WORDS from algorithms.

Last edited by clintonslayton76; 17th February 2018 at 02:30 PM.
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  #12  
Old 17th February 2018, 05:41 PM
clintonslayton76 clintonslayton76 is offline
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Misstatement

Quote:
Because I do not have access to algorithms used by FTDNA to determine if a 1900 CM share is biased toward 1) Full Siblings or 2) Grandparent/grandchild, aunt-or-uncle/niece-or-nephew, half-siblings,
This was poorly expressed: 1975 cM will show Full Siblings, Half Siblings, Grandparent/ Grandchild, Aunt/ Niece, but cannot determine which it is. Whereas, 1877 cM will show Half Siblings, Grandparent/ Grandchild, Uncle/ Nephew or Niece. Note that only 100cM loss drops the Full Sibling possiblity from the second match.

What I meant to express was: I do not know the "breakpoint" that FTDNA uses to determine one from the other, but there are overlaps, acc to genetic literature, where a clear-cut determination is probablistic but not proveable for one or the other. So throwing in the idea of incest cannot vastly alter the cM share between the siblings who produced children or the children-siblings between themselves, but between parents and children, refer to the links at my previous posting or spruitheans (identical in location but not in form).

Run of Homozygosity (ROH) is the issue jotunn needs to look at.
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  #13  
Old 18th February 2018, 08:04 AM
jötunn jötunn is offline
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So if I understand properly, father´s and mother´s common siblings may be shown as parents too, right?

And, for example if my father had an identical twin, it will show two fathers for me too, right?
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  #14  
Old 18th February 2018, 08:25 AM
spruithean spruithean is offline
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Quote:
Originally Posted by jötunn View Post
So if I understand properly, father´s and mother´s common siblings may be shown as parents too, right?
Not necessarily, as siblings do not inherit equal amounts of DNA from their parents.
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  #15  
Old 18th February 2018, 09:44 AM
JMAisHere JMAisHere is offline
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Quote:
Originally Posted by jötunn View Post
So if I understand properly, father´s and mother´s common siblings may be shown as parents too, right?
Example.
Code:
+--------+      +--------+
| Grand  |      | Grand  |
| Parents|      | Parents|
+---+----+      +----+---+
    |                |
+---+---+       +----+---+
| Father|       | Mother |
+---+---+       +----+---+
    |                |
    +-------+--------+
            |
+-------+   |   +---------+
|  You  | --+-- | Sibling |
+-------+       +---------+
Let say all of you have tested.

Now when you login to your account it will tell you the following.

GrandParents = Half Siblings, Grandparent/ Grandchild, Uncle/ Nephew
Father & Mother = Parent/Child
Sibling = Full Siblings

Observe there is no gender information.

Quote:
And, for example if my father had an identical twin, it will show two fathers for me too, right?
You will not see two father you will have 2*Parent/Child

Something for you to understand, FTDNA dosn't make a familytree for you. It will only suggest relationship range. Then you have to make "linked relationship" to distinguish father/mother/child/siblings etc.

After you make "linked relationship" FTDNA will attempt to sort out your matches to father/mother branches nothing more (you still have to make your "linked relations").
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  #16  
Old 19th February 2018, 03:23 AM
jötunn jötunn is offline
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But generally parent/child is easy to distinguish using gender and birthdate if it's available.

So then... in some situations I may end up having 10 parents. Praise Heimdallr!
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  #17  
Old 20th February 2018, 11:54 AM
prairielad prairielad is offline
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Quote:
Originally Posted by jötunn View Post
But generally parent/child is easy to distinguish using gender and birthdate if it's available.

So then... in some situations I may end up having 10 parents. Praise Heimdallr!
No, you can only show parent/child relationship to each parent with a few exceptions.
Exceptions- will show parent child relationship to oneself if have two kits in database for same person, or have an identical twin in database.

Parent/child relationship shares approx 3500cM. This is half identical amount, total amount of cM on your maternal or paternal chromosomes. Amounts are always given in half identical. In reality we have a total of 3500cM on our maternal chromosomes and 3500cM on our paternal chromosomes, total of 7000cM

Siblings (other then identical twins), grandparents and aunt/uncle (unless identical twin of parent) will not show parent child relationship,they will not share the 3500cM amount, they will share under 3000cM

Last edited by prairielad; 20th February 2018 at 12:02 PM.
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  #18  
Old 20th February 2018, 02:30 PM
abuelita abuelita is offline
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Quote:
Originally Posted by jötunn View Post
So if I understand properly, father´s and mother´s common siblings may be shown as parents too, right?

And, for example if my father had an identical twin, it will show two fathers for me too, right?
Yes. In our family, identical twins are shown in FT as "Parent/Child 3,384 267" You can see that they are, instead, monozygotic twins by looking at them in gedmatch.

Their nieces/nephews have the same entries as their own children:
Parent/Child 3,384 267 is the daughter of one twin
Parent/Child 3,384 267 is a niece of that same twin

And the children all have three parents:
Parent/Child 3,383 267 (actual mother)
Parent/Child 3,383 267 (aunt)
Parent/Child 3,381 267 (father)
In that order. The father's comment? "That's not fair! I'm 3rd?"

A full sibling of the twins has identical entries for each of them:
Full Siblings 2,817 213
Full Siblings 2,817 213

And yes, it was totally unnecessary to test both twins, but one of them could not otherwise be convinced that they were incontrovertibly "identical"
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