Tag: GEDmatch

cM – Centimorgans

I had not encountered this word before today but with so many adoptees (including my mom and myself as the child of two adoptees) turning to inexpensive DNA testing for answers to the black hold of identity that adoption placed into our knowledge of our origins, I felt it worthwhile to share some knowledge about this word that I discovered today.

Therefore, I was attracted to an article in Family Tree. LINK>DNA Q&A: How Are Adoptees Related to Their DNA Matches?

The Question – I’m a 33-year-old adoptee, and I’ve tested my autosomal DNA at 23andme.com, AncestryDNA and Family Tree DNA. AncestryDNA predicts my closest match there as “Close family—first cousins.” This match and I share 1,622 centimorgans of DNA across 75 DNA segments. The person doesn’t have a family tree attached to his profile and hasn’t uploaded his results to GEDmatch. I don’t know how old he is. What’s our likely relationship?

The Answer – A close match is the goal of most adoptees who turn to genetic genealogy testing, as this can help reveal genetic heritage. Once you’ve identified a close match, the next step is to determine the most likely genealogical relationship with that match, which will help you figure out how the match fits within the family tree that’s beginning to reveal itself.

All the testing companies now provide the total amount of DNA (measured in centimorgans, or cM) shared with each genetic match, information that can be vital for determining the genealogical relationship. A cM is a measurement of the distance between genetic markers on the DNA based on the expected frequency of recombination with each generation. On average, one cM equals one million base pairs, although this can vary.

Once you know the number of shared centimorgans, your first stop for estimating a relationship is the International Society of Genetic Genealogy’s (ISOGG) LINK>Autosomal DNA Statistics page. This page contains a table summarizing the average amount of DNA (in percentages and centimorgans) shared in a wide variety of genealogical relationships.

Remember that these figures are the average amount of DNA that relatives will share; thus, the actual amount of shared DNA will likely vary. About half the time, the amount of shared DNA will be more than the average, and about half the time the amount will be less than the average. Additionally, if the two relatives are related through more than one recent common ancestor, the relatives could share more DNA than expected.

According to AncestryDNA, you share 1,622 cM of DNA with your close match. The closest category on the ISOGG’s chart is “Grandparent/grandchild, aunt/uncle/niece/nephew, half-sibling,” relationships predicted to share 1,700 cM, or 25 percent of their DNA. The actual and estimated figures are close enough to be very confident that you and your match have one of these relationships, provided that you aren’t related through multiple ancestors.

Another resource you should use is the LINK>Shared cM Project, which collects information about actual ranges of shared cM for different genealogical relationships. Last year, the project gathered more than 7,500 data points related to amounts of shared DNA. It also visualizes the distributions for ranges of DNA shared by various relationships.

The “Degree 2” relationship includes Aunt/Uncle, Grandparent/Grandchild, and Half Siblings. The shared amount of 1,622 cM falls within the Degree 2 range, but not within any other ranges. For example, a shared amount of 600 cM would fall within the range for Degree 5 and Degree 6, giving a wider array of possible relationships.

Based on the ISOGG and Shared cM Project pages, it’s likely that your close match (a male) at AncestryDNA is one of these:

  • your grandfather (at age 33, you’re unlikely to be a grandmother yourself)
  • your uncle
  • nephew, the son of a full sister or brother (if the nephew were the son of a half-sibling, you and he would share closer to 850 cM of DNA)
  • your half-brother

Knowing the age of the match would help you decide between grandfather and uncle/nephew/half-sibling. However, if your match doesn’t provide his age and doesn’t respond to requests for additional information, AncestryDNA offers a tool you can use to further examine this relationship: Shared Matches.

Shared Matches lets you see matches who appear on both your and your relative’s match lists. Although you can check for shared matches with anyone in your match list, you’ll see only individuals you share with that match at the fourth cousin or closer level.

If you share any matches with your relative, examine their profiles for family trees. These may provide other helpful information about this person who is likely your grandfather, uncle, nephew, or half-brother.

DNA Changes Everything

The thought that a woman can carry a developing baby in her womb for the full gestation term and give birth, then abandon that baby in harsh circumstances is truly beyond my own understanding.  While I am Pro-Life (and my definition means not only birthing but supporting every mother and child, which some of the fanatics don’t go that far, just saying) and yet want abortion to remain safe and legal, there are better ways of dealing with a child if the mother can’t cope with raising that baby.

Yet another story of DNA discovering the identity of a mother who abandoned her baby came to my awareness today.  Police have worked with forensic genealogists to analyze the DNA of deceased abandoned babies and their probable mother utilizing genealogy websites, the same technique that in 2018 helped investigators to identify the suspected Golden State Killer.  The new technology understandably alarms privacy advocates while it honestly excites law enforcement officials who say that it provides a crucial new tool for identifying criminals.

On January 2 1988, police found a newborn swaddled in blankets, resting at the base of a tree that was hidden from the road.  He had died of exposure to the frigid weather.  The baby was named David Paul and buried in Walnut Grove Cemetery by police in Meriden Connecticut.

Not only is DNA matching helping adoptees in closed adoptions rediscover their original families as it has definitely assisted me but it is also discovering these tragic mothers.  It was on the 32nd anniversary of the dead child’s discovery that two detectives confronted the woman who was indeed his mother.

She said that, “she had been waiting 32 years for the day in which the police would be knocking on her door regarding this incident.”  What an awful secret to live for decades knowing.  Colleen Fitzpatrick of IdentiFinders International chose to use this baby’s case to test whether autosomal SNP testing could help identify people from their DNA. In the months that followed, she used the genealogical website GEDmatch to map the baby’s and mother’s family trees.

The baby’s mother did express remorse for abandoning him.  She admitted that she was in a bad state of mind when her baby was born. Then 25, she said she hid her pregnancy under loose clothing and delivered the child by herself at home.  She also did try to save him by calling a local fire department and telling them in vague language that there was something they needed to look for in the parking lot. Sadly, the first responders did not know that they were looking for a baby and so did not find him.

The mother will not be charged because the state has a 20-year statute of limitations on manslaughter cases.  She may feel some relief that what she did is no longer a secret.