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Family Finder Advanced Topics Advanced discussion about Family Tree DNA's Family Finder Product.

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  #1  
Old 9th July 2015, 08:36 AM
Illumina Illumina is offline
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From whom I inherited more DNA grandpa or grandma?

Hi everyone!

I would like to know whether it's possible to know from which of our grandparents we got more DNA?

For example: I have my mother and my maternal grandfather tested on FTDNA. With mom I share a total of 3382.96 cM and a longest block of 266.11 cM. With my maternal grandpa I share 1841.26 cM and a longest block of 189.14 cM. Unfortunately, my maternal grandmother is deceased and we couldn't test her.

I'm just curious to know from which of my maternal parents I inherited more DNA.

Any idea or insight?
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  #2  
Old 9th July 2015, 07:21 PM
Kathy Johnston Kathy Johnston is offline
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Quote:
Originally Posted by Illumina View Post
Hi everyone!

I would like to know whether it's possible to know from which of our grandparents we got more DNA?

For example: I have my mother and my maternal grandfather tested on FTDNA. With mom I share a total of 3382.96 cM and a longest block of 266.11 cM. With my maternal grandpa I share 1841.26 cM and a longest block of 189.14 cM. Unfortunately, my maternal grandmother is deceased and we couldn't test her.

I'm just curious to know from which of my maternal parents I inherited more DNA.

Any idea or insight?
Theoretically you could subtract to get the DNA shared with your grandpa but it would not be exact. A few of the smaller segments in the current calculation could be identical by state (coincidental) and not really coming from your grandma after all. So the 1841.26 could be slightly overestimated. I don't think it is very far off.
3382.96 - 1841.26 = 1541.7 cM from Grandpa

I would say you may have received more from the grandfather than the grandmother. FTDNA does not measure the X chromosome but at other companies, that plays a role too in the totals. The 1841 cM seems a little higher than average from FTDNA. I usually see somewhere around 1700 cM being reported as typical between grandparent and grandchild at this company but I have not looked at very many families.

People who have true calculations from both maternal grandparents and both paternal should be able to weigh in here...

I remember seeing as high a difference as one child getting 1267 cM from one grandparent and 2154 cM from the other grandparent on the paternal side. 3421 - 3383 has only 38 cM over the total received from the father so I think the subtraction in the first calculation above is a fairly close estimate.

Fathers make fewer crossovers than mothers so the spread in the grandchildren may be higher. It would be an interesting study to do.
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  #3  
Old 9th July 2015, 10:49 PM
MoberlyDrake MoberlyDrake is offline
mtDNA: T2b5 | Y-DNA: J-M172
 
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The average figure is 25% from each grandparent. Does anyone know the upper and lower values?

My mother has one American (colonial ancestors, not native) grandparent. The other 3 were children of French and German immigrants.

Mom has 412 matches. Her 3rd cousin has 1502. I haven't seen his tree, but I assume he has more colonial American and UK lines than Mom does.

My father's parents immigrated from Italy. He has 35 matches.

I have 251 matches.
My double cousin has 205 matches.
Her brother has 185 matches.

Either Mom got more DNA from her American grandparent than her brother did, or she passed more of his DNA on to me, than her brother passed to his children. Unfortunately, my uncle is deceased, so I cannot test him to see how he and Mom compare.

On the ethnicity tests at all 3 companies, Mom gets a much higher percentage of British Isles than expected.

It would be interesting if those who have had more than one grandparent tested would post the amounts of shared DNA here, perhaps stating paternal or maternal grandfather or grandmother. Great-grandparents would be interesting too, but I suspect few have been able to test more than one great-grandparent.
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  #4  
Old 9th July 2015, 11:25 PM
prairielad prairielad is offline
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Location: Canada
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I agree, you inherited approx. 1541.7 cM from your maternal Grandmother, any spot you do not match your maternal Grandfather will be DNA from your maternal Grandmother (We have approx. 3384cm on our maternal Chromosomes and 3384cM on our paternal chromosomes, that is 3384cM times 2 = approx. 6768cm total)

approx. 3384cM (your total maternal DNA)- 1841.26cM (DNA you share with maternal Grandfather)= 1542.74cM (remaining DNA you must share from maternal Grandmother)

1542.74 divide by 3384 = 45.59% of maternal DNA is from maternal Grandmother (22.79% of Total DNA)

1841.26 divide by 3384 = 54.41% of maternal DNA is from maternal Grandfather (27.21% of Total DNA)

On average you share around 25% of each Grandparent

Below is what myself and 5 siblings share with my paternal Grandparents
Sister 1
29.44% Grandmother
20.56% Grandfather

Myself
19.50% Grandmother
30.50% Grandfather

Brother 1
21.78% Grandmother
28.22% Grandfather

Sister 2
24.02% Grandmother
25.96% Grandfather

Brother 2
26.68 Grandmother
23.32 Grandfather

Sister 3
23.82% Grandmother
26.18% Grandfather

On average we share 24.21% with our paternal Grandmother
(29.44+19.50+21.78+24.04+26.68+23.82)/6= 24.21%


On average we share 25.79% with our paternal Grandfather
(20.56+30.50+28.22+25.96+23.32+26.18)/6= 25.79%
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  #5  
Old 11th July 2015, 11:27 AM
Kathy Johnston Kathy Johnston is offline
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Originally Posted by Kathy Johnston View Post
Theoretically you could subtract to get the DNA shared with your grandpa but it would not be exact. A few of the smaller segments in the current calculation could be identical by state (coincidental) and not really coming from your grandma after all. So the 1841.26 could be slightly overestimated. I don't think it is very far off.
3382.96 - 1841.26 = 1541.7 cM from Grandpa [CORRECTION Grandma]

I would say you may have received more from the grandfather than the grandmother. FTDNA does not measure the X <snip>
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  #6  
Old 13th July 2015, 06:34 PM
Illumina Illumina is offline
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Thank you all for sharing your knowledge with me
I've really appreaciated.
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