Half Siblings?

[tab1968]

Hello.

I have a issue I would like some feedback on.

I manage 2 kits for 2 sisters. As far as I knew they were 100% related meaning they had the same parents. When the younger sisters Family Finder Results came in it is listing them as Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew.

Now before I bring this information to these people I want to make sure the results are accurate an answer coming questions up front.

They were both tested Family Finder by FTDNA.

Is there a chance the results are incorrect? Maybe an error in the results?

Can they still be full sisters with a Shared cM of 1664.42?

If it is true that they are half siblings, is there a way to find out in Family Finder if it through their mother’s side of fathers side?

Any info would be appreciated.

Todd

[madman]

They are half siblings there 0% chance being full sisters with only 1664.42cm

Hello.

I have a issue I would like some feedback on.

I manage 2 kits for 2 sisters. As far as I knew they were 100% related meaning they had the same parents. When the younger sisters Family Finder Results came in it is listing them as Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew.

Now before I bring this information to these people I want to make sure the results are accurate an answer coming questions up front.

They were both tested Family Finder by FTDNA.

Is there a chance the results are incorrect? Maybe an error in the results?

Can they still be full sisters with a Shared cM of 1664.42?

If it is true that they are half siblings, is there a way to find out in Family Finder if it through their mother’s side of fathers side?

Any info would be appreciated.

Todd

[1_mke]

The easiest way to tell for sure is to see how much (if any) full matching they have. I don't think this is possible on FTDNA? But it is possible on Gedmatch. Full siblings will have at least some full matching.

Half siblings will only have half identical matching, assuming they aren't cousins of some sort on the non shared parents side.

Average would be about 25% fully identical matching and 25% half identical matching for 50% total matching.

[1_mke]

Having said that, it's very unlikely but not impossible for them to be full siblings given the amount of matching you list. It's theoretically possible for full siblings to have 0% matching but the odds of that happening in the entire history of the universe are probably low.

I don't know what the minimum recorded matching is between full siblings but it would be interesting to know. I'm sure it is well below 50%

[mkdexter]

Yes, sounds like a half sib match like the others have said.

As for paternal or maternal side? Compare them on their X chromosome. Any large gaps (over 15cM) would indicate they have the same mother. Any full match will not indicate either side, could be on the father or mother's side. But by chance they have a part of the X they do not share, that would indicate the same mother. Let us know what you find on X comparisons please.

[prairielad]

you can run raw data through David Pikes Utility and it will give you Double Segment Match length and Single Segment Match lengths for both autosomal raw data and X raw Data

http://www.math.mun.ca/~dapike/FF23utils/pair-comp.php

For example
Two full siblings will show larger Double segment lengths (lengths from both maternal and paternal chromosomes)as well as single strand lengths.

While half siblings will show mainly Single segment lengths and maybe small Double strand lengths.

In regards to X, my 3 full sisters show the following to each other using David Pikes Utilities.

Sister 1 to Sister 2 (They share full paternal X and a Full uncombined maternal X)(they are not twins)
Chr X has a Double Segment Match of length 17797 from position 1370495 to position 154551755 (153.18 Mb)
Total Mb: 153.18

Chr X has a Single Segment Match of length 17797 from position 1370495 to position 154551755 (153.18 Mb))
Total Mb: 153.18

Sister 1 to Sister 3 (They share full paternal X and parts of maternal X - different portions of mothers recombined maternal/paternal X)

Chr X has a Double Segment Match of length 7238 from position 34794299 to position 116140699 ( 81.35 Mb)
Total Mb: 81.35

Chr X has a Single Segment Match of length 17797 from position 1370495 to position 154551755 (153.18 Mb)
Total Mb: 153.18

Sister 2 to Sister 3 (Identical sharing as Sister 1 to Sister 3)

[tab1968]

Results

Thanks for all the information. I learn a lot on these forums.

They do not have a lot of common relative matches to each other at all compared to other brothers and sisters I have seen.

For FTDNA X Chromosome matching Centimorgans I got:
50.91
40.89
12.2

For David Pike I could not get a result using the X files. I could do the autosomal and got Total Mb: 1501.45.

For Gedmatch using the Autosomal Comparison I got:
Largest segment = 118.6 cM
Total of segments > 7 cM = 1,739.5 cM
Estimated number of generations to MRCA = 1.5

GedMatch X-DNA Comparison I got:
Largest segment = 49.9 cM
Total of segments > 3 cM = 114.7 cM Actual.
Sex-Adjusted total of segments = 57.3 cM Equivalent.

Let me know what you think. Both parents have passed away.

Todd

[prairielad]

..........

For David Pike I could not get a result using the X files. I could do the autosomal and got Total Mb: 1501.45.

.........

Depending on when FF test was done, you will have to create a new X raw data file (.csv or txt). Older tests X raw data are sorted by RSID, David Pikes Utility requires it to be sorted by position (smallest to largest).

Format example(sorted by position)
"rs17883004","X","1370495","AA"
"rs5939319","X","2710157","AG"
"rs1419931","X","2713633","GG"
"rs311173","X","2722661","CC"
"rs311183","X","2724756","TT"

[Kathy Johnston]

Thanks for all the information. I learn a lot on these forums.

They do not have a lot of common relative matches to each other at all compared to other brothers and sisters I have seen.

For FTDNA X Chromosome matching Centimorgans I got:
50.91
40.89
12.2

For David Pike I could not get a result using the X files. I could do the autosomal and got Total Mb: 1501.45.

For Gedmatch using the Autosomal Comparison I got:
Largest segment = 118.6 cM
Total of segments > 7 cM = 1,739.5 cM
Estimated number of generations to MRCA = 1.5

GedMatch X-DNA Comparison I got:
Largest segment = 49.9 cM
Total of segments > 3 cM = 114.7 cM Actual.
Sex-Adjusted total of segments = 57.3 cM Equivalent.

Let me know what you think. Both parents have passed away.

Todd

When you compare the sisters at GEDmatch, it sounds like there are no "Full Matches" in green. If they matched both parents, you would usually see full matching on the X where they match their mother in green. More importantly, you would also see an entire blue match with the father's X chromosome adding up to about 196 cM. I think these sisters have different fathers. If the blue is not continuous, you really have to entertain the possibility that there is an NPE (non-paternity event). Full sisters normally inherit an X chromosome intact from the father and they match each other on that segment. If there is no green, but rather several blue segments on the X, then the blue came from the mother and they are half sisters.

[mkdexter]

Thanks for all the information. I learn a lot on these forums.

They do not have a lot of common relative matches to each other at all compared to other brothers and sisters I have seen.

For FTDNA X Chromosome matching Centimorgans I got:
50.91
40.89
12.2

For David Pike I could not get a result using the X files. I could do the autosomal and got Total Mb: 1501.45.

For Gedmatch using the Autosomal Comparison I got:
Largest segment = 118.6 cM
Total of segments > 7 cM = 1,739.5 cM
Estimated number of generations to MRCA = 1.5

GedMatch X-DNA Comparison I got:
Largest segment = 49.9 cM
Total of segments > 3 cM = 114.7 cM Actual.
Sex-Adjusted total of segments = 57.3 cM Equivalent.

Let me know what you think. Both parents have passed away.

Todd

You have two half sisters with the same mother. That is the most probable answer considering the readings you have listed here and prior.

Matt.

[mkdexter]

When you compare the sisters at GEDmatch, it sounds like there are no "Full Matches" in green. If they matched both parents, you would usually see full matching on the X where they match their mother in green. More importantly, you would also see an entire blue match with the father's X chromosome adding up to about 196 cM. I think these sisters have different fathers. If the blue is not continuous, you really have to entertain the possibility that there is an NPE (non-paternity event). Full sisters normally inherit an X chromosome intact from the father and they match each other on that segment. If there is no green, but rather several blue segments on the X, then the blue came from the mother and they are half sisters.

oops.. it was already answered... well.. two (probably more of us) agree you have half sisters here with the same mother.

[tab1968]

Thanks for all the answers it answered a lot.

Todd