DNA download from ancestry and 23andme for specific ancestors

+2 votes
174 views

I have an ancestor named Sir Thomas Morgan MP (1534 - 1603) https://www.wikitree.com/wiki/Morgan-901 I would like to compare our DNA or see if I have any of his DNA.  It seems complicated by the way it is described. https://www.wikitree.com/treewidget/Morgan-901/890

in Genealogy Help by anonymous G2G Crew (340 points)
retagged by Lynda Crackett
Katie, please do not use my profile as the link to this question.  If you wish to ask me this question, post it on my profile.  However, I can tell you now that I have no idea as I am not all that well versed regarding DNA and do not have any connection to Morgan.  Thanks, Cindy
I guess I need more instruction on the propriety of the question, which seems OK to me. The profile is listed as open, and Cindy is not listed as a profile manager.
Katie, I see that you are still registered as a Guest member of Wikitree. Would you be interested in completing the membership process so that you can begin to develop your branches of the tree?

1 Answer

+11 votes
Sir Thomas Morgan was born in 1534. It is extremely unlikely that you will be able to use your 23andMe auDNA test to confirm any relationship to him. auDNA tests such as 23andMe, Ancestry, and Family Finder are generally only useful for confirming relationships back to about 3rd to 4th or possibly 5th cousins (people who share 2nd - 4th great grandparents).
by Kay Wilson G2G6 Pilot (187k points)
Hi Kay,

Wouldn't it be possible to confirm a relationship with a cousin who already has confirmed the relationship to Sir Thomas Morgan via the standard genealogical route and thus use DNA testing to find a connection to that possible ancestor?

Isn't it also possible to find matching DNA segments to some ancestors--not necessarily Sir Thomas Morgan, but possibly...--which might establish some ancestral relationship to that individual?

For example, I've compared my DNA to a number of ancient DNA samples and have results which seem to suggest that they may have been ancestors, or at least share ancestry.

It seems to me that DNA testing does help establish ancestral links well beyond 3rd to 5th cousins, but not with any degree of accuracy. From what I've gathered--and I'm a novice, so I'm not certain about this--DNA testing isn't useless beyond the 4th or 5th generation, but is so watered down that it can't be used to make accurate determination of relationships. Plus, we don't have the DNA of many ancestors, so that is a further difficulty.

On the other hand, the more people that are tested, the more likely we will be able to assemble a better picture of both human DNA relationships, but also a more complete "universal" human family tree. (Obviously there will be billions who will never be on that tree, since so much information has been lost. But we should be able to establish a fairly comprehensive genealogy as more DNA results are added.)

Hi, John. I'm kinda peepin' in from the peanut gallery here, but wanted to offer a few comments. Given that your note had about five separate questions/issues, all that loud groaning you hear are the G2G regulars familiar with my tendency toward...er, adequate word count.  wink  But it's Friday night and I really will try to keep this as brief as I can. Which won't be all that brief. Run away while you can!

Er...Part 1.

"Wouldn't it be possible to confirm a relationship with a cousin who already has confirmed the relationship to Sir Thomas Morgan via the standard genealogical route and thus use DNA testing to find a connection to that possible ancestor?"

Like any good consultant, my first answer is, "It depends." So long as we aren't using the word "confirm" synonymously with "prove," it's a yes on two qualified fronts. DNA evidence of any kind cannot be applied to genealogy in a vacuum. The paper-trail always has to be there. The only possible exceptions are autosomal DNA with respect to a twin, parent/child, or full-sibling. Even at the level of half-sibling, we can't determine the relationship with only that approximate 1,700-1,800cM shared amount because the same expected sharing is seen with grandparents, grandchildren, aunts/uncles, and nieces/nephews.

Similarly, DNA can't be used as evidence unless it extends back to the MRCA. For example, if I have an ancestral tree that shows me descending from Sir Thomas Morgan, the fact that your autosomal DNA has a solid match to mine means nothing with respect to Sir Thomas. It shows that you and I share significant segments of our atDNA, but a single error in the paper trail of my tree negates any possible genetic relationship to Thomas Morgan, and negates DNA as evidence.

But let's jump ahead to the issue of autosomal DNA use and generational distance, and then circle back. Categorically, autosomal DNA is of no genealogical evidentiary use many generations removed. Just isn't. At each birth event, atDNA is randomized through the process called crossover during meiosis, when the gamete is created, and each of the parents contribute 50% of their DNA to the zygote. That "rule of 50" begins to vary even with grandparents: neither of the four are likely to have contributed exactly 25% to the grandchild. All that randomness is nature's wonderful schema to insure enough genetic diversity for species survival even when an initial population may be quite small.

If we aren't exhuming an ancestor for a test, we have to rely on living individuals. By 5th cousins and shared 4g-grandparents, 12 birth events, the expected DNA sharing is 0.049%. By 7th cousins, 16 birth events, it's functionally zero: 0.003%. If you were to exhume your 14g-grandparents and have the remains tested, the likelihood of any identifiable DNA sharing would still be functionally zero.

Something I hear quite a lot nowadays is, "But that's just the theoretical average. You said it was random." And then there's usually a finger pointing to Blaine Bettinger's crowd-sourced data at the Shared cM Project, which shows that 7th cousins have been reported (again, self-reported, not scientifically studied) as sharing as much as 57cM. Extremely useful information at the Project, but the assumption that the median sharing amounts shown are valid for relationship determination past about 3rd cousins is incorrect.

Here's the problem with it. Every family tree in existence contains some degree of pedigree collapse, of having fewer biological grandparents at a given level than the progression of 4, 8, 16...512, 1024, and so on. Pedigree collapse makes it exceedingly complex and difficult to validate an autosomal DNA connection, precisely because the average expected sharing amounts get thrown out the window and you have no DNA basis to help determine relationship. It's the reason it's almost impossible to use autosomal DNA beyond only one or two generations in endogamous groups like the Ashkenazi or certain Pacific Island populations, and one reason why many of the autosomal DNA triangulations I've seen are indefensible or even obviously incorrect. If you share way more than the theoretical expected average for a given relationship, there's a reason...and it ain't just randomization.

We have a population geneticist here on WikiTree named Brad Foley who is going to take great exception at the over-generalization I'm about to make. But I'll take one for the team. Within your autosomes you have what can be thought of as Population DNA, and Family DNA. When we talk about the amount of DNA you share with your cousins and genealogical ancestors, we're talking about Family DNA.

But all humans are 99.9% DNA identical; we're all pretty much alike. Which makes sense because if mutation goes messing around too much with our important protein-producing genes (with apologies to Stan Lee and the X-Men) the organism just ain't got a great chance of surviving to reproduce. So we all--you, your next-door neighbor, and Anzick-1, the infant Paleo-Indian remains in Montana dating back to about 12,500 BCE--are all pretty much alike.

Part 2

The current state of direct-to-consumer $99 testing is that it takes a look at about 700,000 SNPs (single nucleotide polymorphisms), or fewer. The genealogy market is not very important revenue-wise to Illumina, the company that makes all the nifty microarray chips that can translate squishy biological suspension into digital readouts. So the chips the genealogy testing companies use are cross-purposed, primarily for academic population studies. Which works for us because the specific loci along the chromosomes they sample are ones which have been identified to change via mutation with a reasonable frequency; very few--but some--of the tested SNPs are contained within vital protein-encoding genes.

We're testing about 0.023% of the genome. A whole massive boatload of mathematical assumptions and imputation and probability and genotyping go into giving us data we can work with genealogically. When you dig into it all, you come out frankly surprised that we can be even remotely as accurate as we are. We typically measure segment size in centiMorgans, which isn't a physical measurement at all; it uses linear equations to estimate the frequency of crossover points along a chromosome--and the number of these points differ by as much as 30% between a female and a male genome map, so what we see from GEDmatch and the testing companies is what's called a "sex-averaged" value--in order to arrive at a comparative figure of relatedness, the centiMorgan. Not only that, but a segment of 7cM may have been assumed by a sequence of, say, 1,000 identical SNPs...along a stretch of chromosome that contains over 5 million base pairs. We're assuming that all those base pairs in between are identical if there are only a certain percentage of SNPs in the mix that don't match or are null no-calls, and despite the exact-looking start and stop positions you see at GEDmatch and elsewhere, we really don't know where the physical segment begins and ends: we can only measure to the matching SNPs.

To get to the point in the future that we can begin working with fully-sequenced genomes in the consumer market, we'll need a next-gen evolution in computing power. Gettin' all geeky, a medium-resolution full-genome BAM file, the way the full genomic sequence is stored, requires about 150Gb plus indexing overhead. Technology simply isn't at a point where we can deliver comparisons online, on demand, of even a few full genomes at a time, much less thousands or millions.

Okay. Net message is that our current technology with autosomal DNA for genealogy is really rather coarse and crude. That's why every genetic genealogist with a rep that I know of says to throw out the notion of very small segments. There can easily be a 4cM or 5cM difference between the sex-averaged numbers we see and what the valuations would be if applied to the female vs. male genome map. Not to mention that the versions of the genome maps change periodically and, again as an example only, GEDmatch is using hg36 while most universities have moved on to hg38. We really can't even compare true apples-to-apples at that most basic level. The different maps have different base pair numberings for the identified reference clusters (the actual nucleotides being identified).

So, no. Right now, autosomal DNA cannot be used as genealogical evidence dozens of generations into the past. Even Jim Bartlett, a proponent of atDNA triangulation, will use a 7cM segment in a triangulation group only because he's amassed well over 10,000 triangulated segments in over 580 triangulation groups; he knows to question or eliminate pile-up regions; and he knows to question and thoroughly research DNA evidence of pedigree collapse. One 7cM segment in the mix that turns out to be false will be only a rounding error and won't impact the validity of the triangulation group.

And no living person's atDNA can verify a genealogical linkage to any ancient remains. A linkage per Population DNA, yes. That's how the testing companies attempt to market their "ethnicity" reports. There are genomic differences typical of broad population groups, small DNA segments that seem to remain intact over even thousands of years. But the existing science is imprecise and dependent upon the datasets used and the mathematical algorithms employed in the genotyping. And while whole-genome sequencing has been improving rapidly since 2015 in academia, it's still going to take some time, likely years, before a test at, say, 23andMe and AncestryDNA will agree on the same person's population admixture.

Circling back as promised to how autosomal DNA can be used to validate a biological link back to ol' Sir Thomas Morgan. And it's how every female genealogist has to work with yDNA.

The uniparental DNA, yDNA and mtDNA, don't undergo crossover and aren't combined with the other parent's DNA to form the zygote. They are passed down generation to generation entirely intact; the only changes that occur do so due to mutations. The mitochondrial DNA molecule is really too small, only 16,569 base pairs, to be of much use as positive genealogical evidence. It's great to disprove a matrilineal hypothesis, but there just aren't enough available nucleotide combinations that can mutate without harming the organism to give us enough differentiation. Millions of living people have identical mtDNA.

The Y-chromosome, on the other hand, has over 58 million base pairs and only twice the number of coding genes as the minuscule mitochondrion. All that other stuff is free (we think) to mutate and provide oodles of differentiations that can be mapped back hundreds of generations.

If a few of Sir Thomas Morgan's direct paternal descendants, in an unbroken chain, have carefully compiled their paper-trail genealogy and carefully triangulated their yDNA results, then someone whose autosomal DNA is a strong match to those men can use that as DNA evidence back to Sir Thomas. Mind you, this is not a WikiTree "confirmed with DNA" policy or practice, but it is a commonly used tool in genetic genealogy and why many of the FTDNA surname DNA projects have as many women members as men: they're managing the yDNA kits of male relatives.

Now that I've kept this incredibly brief, as promised....  angel

What he said!  laugh

And I liked your teaching point about differentiating 'Population DNA' from 'Family DNA'.

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