OMG – Another Half-Sibling

Half-Siblings provide the proof

Brown, DNA
By Don Taylor

Thanks to autosomal DNA testing, I’ve learned who my biological father is. I have discovered and met some of my “new” half-siblings on my biological father’s side. I have also discovered that my wife has a previously unknown half-sister. Now, due to DNA testing, I’ve found that my mother has a previously unknown half-sister.

It began with an email from (I’ll call her) HC, who indicated that Ancestry DNA was saying that she and I were first or second cousins. The Ancestry match reported that she and I share 460cM of material.  A look at our trees showed no surnames in common. Ancestry allows you to view a match and see who also shares that match.  My half-sister, Glennis, was also a match and shares, even more, DNA (522 centimorgans) than I share with HC.  That proves that the match was on my maternal side as Glennis and I share a common mother.

HC & I share 460cM

Through an exchange of messages, I learned that HC’s mother was adopted, was born in May of 1938 in Texas, however, her mother was conceived in Minnesota. That narrowed things considerably.  My mom’s Montran/Barber line pretty much was from Michigan; my mom’s Brown/Manning line was from Minnesota. So, it was very likely that the match came from my mother’s father’s side of the family.  Luckily, my mother has a half-sister.  The bad news is that neither my mother or her half-sister, Barbara, tested with Ancestry.

No problem, GEDMatch to the rescue. Although both tested with another service, I had previously exported their data from the other system and imported the data into GEDMatch. If HC was a match with my mother and aunt Barbara, then the common ancestor had to be on their common father’s side. If the match was only with my mother and not my aunt Barbara, then the common ancestor had to be on her Montran side. I know very little about Montran line, so anything could be possible.

HC uploaded her data to GEDMatch and the results were amazing.  She shares over 1000 centimorgans of DNA with BOTH my mother and my aunt Barbara – Proof that the common line is on the Brown side. I like to use The DNA Geek’s chart to quickly see the potential relationships between individuals at a particular centimorgans level. The chart shows that 1000 cM is solidly in the range of Group C relatives. Relationships for Group C include First Cousin, Half Aunt-Uncle/Niece-Nephew, Great-Grand Parent/Child and Great Aunt-Uncle/Niece-Nephew.

Now that I know that the match is on the Brown line I can speculate.

Grandpa Dick

• If Grandpa Dick is the father of HC’s mother, then HC would be the half-niece of my mother and Aunt Barbara.  That fits the amount of DNA Perfectly.
• If one of Grandpa Dick’s brothers were the father of HC’s mother then, HC and my mother would be first cousins once removed and I would expect a DNA match of between 215 and 650.
• Dick’s father died in 1928, so he can’t possibly be the father of HC’s mother, so that scenario isn’t possible.

Finally, I questioned was there is a locational opportunity for Grandpa Dick to be the father. HC’s mother was conceived while her mother was in Deerwood, MN about August of 1938. In 1937, my Grandpa Dick was living in Brainerd, Minnesota, about 18 miles from Deerwood.

I think that is enough to prove the relationship. However, I always like to go the extra mile if possible and prove it beyond the shadow of a doubt. HC’s mother is still alive and recently had her DNA tested. When the results come back, we can confirm this relationship. I expect that the autosomal DNA match with my mother and with Aunt Barbara will be in the 2000cM range – solidly in the half-sibling range.

Additional proof will come through a comparison of the X chromosome. Females have two X-chromosomes (males have an X and a Y).  One of the X chromosomes is from the mother and is recombinant, that is to say, it is a mix of the mother’s X.  The other X chromosome is a replica of the father’s X and is passed on without change.  If HC’s mother and my mother are half-siblings, I would expect to see their X-Chromosome to have a solid match like my mother and her half-sister Barbara have.

X Chromosome match of my mom & Aunt Barbara.

My mother and my Aunt Barbara have a here-to-for completely unknown half-sister. Amazing. I always heard that Grandpa Dick “liked the ladies.”  I guess he did. I now know of four daughters that he fathered, my mom, Aunt Barbara, Aunt Mary Lou, and newly found Aunt Phyllis. I wonder if there are more….

Note:

• I do not typically use the full name of living individuals.
• Of course, if any DNA specialists see anything incorrect with my reasoning above, please let me know via the contact form below.