Tracing a Genetic Inheritance?
June 12, 2017 6:40 AM   Subscribe

A recent blood test of my Caucasian mother revealed Sickle Cell Trait yet nowhere in her genealogical history going back many generations is there anyone from an ethnic group where this is more commonly found (African-Americans, Hispanics, South Asians, Middle East, southern Europe). I'm a student of my family genealogy and, while concerned about the medical issues, am nonetheless thrilled to know that my family is a bit more diverse than anyone realized. Some obvious questions arise, however...

Genetic questions:
1. Would a person with two such genes, aka someone with Sickle Cell Disease, pass down only one gene to their children or would the inheritance be either both genes or none?
2. Is there any way to determine for how many generations this gene has been in my seemingly otherwise northern European genetic code?
3. Can the ethnic origin of the gene be determined by, perhaps, other markers?

Genealogical Questions:
1. Since my mother's family is from the south, is it safe to assume that I have African-American ancestors?
2. What are the odds that such ancestors were slaves? Any chance that there was a loving relationship that simply had to be kept hidden or even pre-date the slavery period?
3. What's the best strategy for unearthing the truth? Will I ever know the truth?
posted by Jamesonian to Science & Nature (10 answers total)
 
Response by poster: To clarify, I am also Caucasian.
posted by Jamesonian at 6:44 AM on June 12, 2017


A parent passes half their DNA to a child. Someone with sickle cell disease has that gene on both chromosomes, so no matter which one the child gets, they will inherit that trait, i.e. all their children will be carriers. Whether they develop the disease depends on which gene they inherit from the other parent.
posted by Flannery Culp at 6:58 AM on June 12, 2017 [1 favorite]


I would suggest you do 23andme for health and ancestry. It costs a bit but what you are interested in is what they do. They also trace back your 'likely' ancestors a few generations back to their likely place of origin, though it's an estimate based on your genes, not a verified family tree. A family tree is likely what you want.
posted by tooloudinhere at 7:17 AM on June 12, 2017 [1 favorite]


Sickle cell trait and sickle cell disease are different; a person who has only one affected gene has the trait, and a person with both genes affected has the disease. Sickle cell trait is less severe.

Sickle cell trait on its own tells you nothing about ethnicity in your family; it is always possible that it was a spontaneous mutation, and though it is more common in certain ethnic groups, that does not mean it is wholly absent in others.
posted by ocherdraco at 7:35 AM on June 12, 2017 [3 favorites]


Mod note: Folks, the question explicitly notes the geographic variety of possible sickle cell trait cohorts, no need to reiterate that back to the asker.
posted by cortex (staff) at 7:56 AM on June 12, 2017


Response by poster: "I would suggest you do 23andme for health and ancestry."

I did, several years ago, and it revealed some trace ancestry from several of the regions in which SCT are found (4% Italy/Greece, 1% Africa, < 1% Middle East). Any of these could have introduced the gene.

"Sickle cell trait and sickle cell disease are different"

I'm very aware of this. While the disease is far more serious, the trait itself could present serious problems under certain conditions.

"Sickle Cell Trait is does not only occur in the African-American population."

Yes, that's why I included the list of primary ethnic groups in my question.
posted by Jamesonian at 7:59 AM on June 12, 2017


Based on my personal experience in genealogy, I would suspect one of two things as most likely:

1. someone "adopted" a cousin or an illegitimate child. Both of these happened a lot!! It is especially common in immigrant situations where it benefits the family to claim a niece as a daughter in order to help her get into the country and of course all the mothers who really grandmothers to the young daughter's baby (which means the know father is wrong) or who adopt their husband's illegitimate child or who benefit from the presumption that when a married women is pregnant, her husband is the father.

2. someone married into the family who "passed" as northern european but was mixed ancestry.
That could be someone with a mixed African heritage, or knowing the level if virulent discrimination against the Italian and other Mediterranean folks, it could have also been almost any of those other groups.

Genetics can tell you some things about possible sources for your genotype but it is not going help with specifics like where it might have entered your family tree and the specifics of the relationship involved.
posted by metahawk at 10:47 AM on June 12, 2017


Since you've done 23andme, you can actually go look at the area of the genome where this gene is present and see where 23andme predicts that area came from. The HBB gene is near the end of the short arm of chromosome 11, so take a look at the "Ancestry Composition Chromosome Painting" thing that 23andme does and see what that area has in terms of ancestry. It would be interesting if any of your trace ancestry overlaps that region.
posted by omnie at 11:25 AM on June 12, 2017 [2 favorites]


1. Since my mother's family is from the south, is it safe to assume that I have African-American ancestors?

Insufficient evidence to prove. But go back far enough and everyone has African ancestors.

2. What are the odds that such ancestors were slaves? Any chance that there was a loving relationship that simply had to be kept hidden or even pre-date the slavery period?

As above - insufficient evidence for a conclusion. But, frankly, if you had ancestors who were slaves, then it's pretty likely that it wasn't consensual. It's hard to have a consensual relationship with someone who owns you, or can own you. How can you consent when you have no bodily autonomy?

Also, America's slave period included, how to put this delicately, quite a lot of raping of slaves. That would be a much more likely source for your potential slave ancestor.

3. What's the best strategy for unearthing the truth? Will I ever know the truth?

Seems highly unlikely unless there is a trove of genealogical records you are not currently aware of.
posted by His thoughts were red thoughts at 3:44 PM on June 12, 2017


Best answer: I am a librarian in North Carolina with some familiarity with genealogy (but am not a genealogist). It's difficult to tackle your question from a genealogical perspective without knowing where your family comes from - the South is a big place!

Questions you could research: what was slavery like in the region your family comes from? Who were their free black neighbors? Did they have other neighbors with diverse backgrounds, such as Sephardic Jews? What was your ancestors' social class? What did they do for a living? Did they own slaves? Are there any known gaps or ambiguities in the documentation of your family tree? Could your family genealogy have errors?

You may not find the answers you're looking for, but if you decide you are curious, you will learn a lot about your ancestors' lives and about their relationship to slavery. Approach your search with an open mind and be prepared to learn upsetting information about your family. Most of us are descended from folks who did and believed repugnant things.
posted by toastedcheese at 6:26 PM on June 13, 2017


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