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Messages - Eric Hatfield

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Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Friday 09 March 18 00:32 GMT (UK)  »
Removed because I got it wrong. Sorry.

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Wednesday 07 March 18 10:37 GMT (UK)  »
Not quite true.  Yes, it would be rare for a person not to inherit any DNA from an ancestor five generations back (a gtgtgt-grandparent).  But just because you inherit DNA from an ancestor doesn't mean your fourth cousin who descends from the same couple will have inherited the same DNA from them that you have.
Hi Hurworth, yes you are right. My first statement was  correct, but only a percentage of 4th cousins will match. I mentioned some of the percentages before, and your reference provides them too. Thanks for the correction.

My point was that while we miss some matches, we also get plenty, which is better than nothing. (It's a bit like paper records. Some church records for example have been lost, some are still available, but that doesn't stop us using what we can find.)

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Wednesday 07 March 18 09:08 GMT (UK)  »
Hi Guy, You say "Eric you seem to know more than Rolf Kohl, Dr.rer.nat. (Ph.D) Ecology & Biology, Ludwig Maximilian University of Munich, for instance,  who states-", but he said the same as I did, except I didn't mention mtDNA, which is quite separate from the 23 chromosomes, but which men inherit just as much as women do. Your quote is about genes, which don't account for all DNA, but only a small part of it.

Which is what I was saying due to DNA dropout (this is where the DNA of a particular ancestor is not passed down to a child, that particular DNA may be passed on to a sibling but the child’s descendants will never carry the “missing” DNA.
Yes, there is a drop off. Nevertheless, some DNA is generally passed down from ancestors in the first 5 generations back. My understanding is that for a person to receive no DNA from such a close ancestor would be rare. So there is almost always enough DNA to form a match between two people with a common ancestor in the last five generations.

As I have said in the past when the science develops it may prove to be of use in genealogy but at present it is far too inaccurate and too expensive to be of any use to the bulk of genealogists.
Ah well, I guess you can ignore it. Meanwhile, so many other people, including a few on this thread, have found it useful, actually indispensable. But let's not go over that ground again shall we?

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Wednesday 07 March 18 09:01 GMT (UK)  »
That is so cool, you are a mine of good information. Thanks.

I actually visited the DNA geek blog just a couple of days ago and asked about the different companies' coverage in different countries, so perhaps this survey is partly as a result.

I hope she gets enough participants to get some reasonable results.

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Wednesday 07 March 18 07:38 GMT (UK)  »

Thanks for that link, I hadn't seen it before, and even though I have been with FTDNA for two and a half years, I learnt quite a lot.
  • Yes, it resolves the question of why you only see closer matches (its Ancestry's chip, not because you haven't unlocked). Thanks for your input too Hurworth, you are right and I was wrong in my guess.
  • Yes, it shows where the different criteria of close, distant, etc, appear on the match list as you asked about and I had forgotten (not just on the chromosome browser, which I knew about).
  • And it explains why many people think that doing the FTDNA test is worthwhile even though they can transfer for free.
I really wish we knew the location of testers in the 4 main companies. I have avoided 23andMe because I thought they were mainly US based, and their testers were maybe more interested in health & medicine issues, and not so helpful with family history enquiries, but that is just an impression. I'm thinking about testing there also now, same reasons as you.

Thanks again. It is good to get clarification.

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Tuesday 06 March 18 23:16 GMT (UK)  »
Hi Guy, thanks for sharing your thinking on this. But I think you may have some misunderstandings about DNA. I am certainly not an expert, but here is a little of what I have learnt from others.

Basically as you go back in time there is far more DNA available than is used to "build" a human body
We don't have to go back in time for that. All of us have a genome where maybe 85% is "non-coding", which means geneticists believe that those segments aren't used to make proteins or perform other useful functions.

But that isn't relevant for genetic genealogy. Testing companies typically test somewhere around 700,000 locations out of more than 3 billion. That is only about 0.02%, but these are the locations which are known to vary. All the rest stay pretty much the same. So even if all of them were tested, they'd tell us very little.

we each inherit 50% of our DNA from our mother and 50% of our DNA from our father but that does not mean we each inherit 50% of our father's DNA and 50% of our mother's DNA.
We do indeed inherit exactly 50% of our DNA from each parent, because we inherit one of each chromosome pair from each. And that inevitably means that we inherit half of each of their DNA.

The only exception to this is the 23rd chromosome, which determines gender. The X chromosome, which both genders have is larger than the Y chromosome which only men have, so a man inherits a longer length of DNA in the 23rd chromosome from his mother than his father. But that fact isn't significant to what we are discussing here.

We inherit approximately (but not exactly) 25% from each of our 4 grandparents (i.e. 2 generations back), approx 12.5% from 3 generations back, approx 6.25% from 4 generations back, approx 3.12% from 5 generations back, etc. The further back we go, the smaller the percentage and the greater the potential for variation.

Which if you understood DNA you would realise that you do not inherit DNA form the bulk of those ancestors.
So, yes, if we go back far enough we will likely not inherit discernible DNA from some ancestors. That was why I limited myself to 5 generations back, so that it is most unlikely that we don't inherit from all of those ancestors. But even if we go further back, we will still inherit discernible DNA from most of them - our DNA has to come from somewhere!

So there are always uncertainties in DNA matching. The experts say that above about 30 cM, we can be 90% confident of a match within 6 generations, whereas down at 12 cM there is little chance (5%) of such a match. The various testing companies use different algorithms to calculate matches - they tend to err slightly on the side of giving you a match to check out even if it is uncertain. But with thousands of matches, there will be many genuine matches, and most of us think it is worthwhile having to dismiss some matches that don't work out for the sake of finding the others that do work out.

So I can only conclude that you have taken an unnecessarily sceptical and not fully accurate view of DNA testing. I hope you find the links I have given helpful in building your understanding, as they have helped me. Thanks.

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Tuesday 06 March 18 21:56 GMT (UK)  »
Hi Margaret,

I haven't unlocked tools at ftDNA, if I can't confirm matches with any close cousins I'm not sure I will be able to do so with more distant ones!
No, I can understand that. I was just checking that that is probably the reason why you only see a limited range of matches.

For searching more distant cousins, way too many to look at individually -
DNA results
Search matches,Top right
Search by name or Birth location
Thanks, I'll look into that.

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Tuesday 06 March 18 11:18 GMT (UK)  »
Hi Guy,

The above figures show why DNA testing is not really worth while for genealogy yet.
You have said this before, but it simply isn't true, for most people at any rate.

Yes, the number of people who have tested is small, but consider:

1. If we consider just 4th cousins or better, which is 5 generations to the common ancestor, each tester will have 63 ancestors (except in endogamous populations). If there are 10 million testers (assuming 5 million are doubled up), then there are potentially 630 million ancestors. Now of course many of those will be multiples also, which is exactly what we want, say half of them = 315m. Virtually everyone I am connected to is in USA (330 m), UK (67m), Canada (38 m) and Australia (25m), a total of 460m. So 630m or 315m ancestors is looking pretty reasonable.

2. If we consider any one of our pairs of ancestors, the ones 5 generations back could easily have several thousands of descendants today. If we make some assumptions, for the purpose of the exercise, of how many children each couple had and how many of them had children, it is possible to make a calculation for each pair.  Assuming only 7, 6, 5, 4 and 3 children for the generations, we'd get roughly 2400 descendants for each 5th generation couple, 360 for 4th, 60 for each 3rd, 12 for each 2nd and 3 for our parents' generation. Multiply that by the number of couples in each generation and the total number of present day descendants of all our ancestors = 16 x 2400 + 8 x 360 + 4 x 60 + 2 x 12 + 1 x 3 = 41,500. If I have done the calculation correctly, that is a very approximate estimation of the total number of possible 4th cousin or better matches any of us have.  If we included out to 8th cousins as Ancestry does (which I think is not generally very useful), then the number would be absolutely enormous. So there is no shortage of potential matches. Of course I don't pretend that these figure are any more than notional, but they are illustrative.

3. And so it is no surprise that I have several hundred (only a few are repeats) 4th cousin matches on Ancestry and FTDNA out of the possible 40 thousand, or whatever the figure is, and 17 thousand Ancestry matches overall.

4. But the real proof, which you seem to have not considered, is that people are finding relatives they couldn't find any other way - adoptees, people with uncertain parentage, people whose ancestors' paper records are lost, etc. If you check out adoptee websites, you'll find plenty of success stories - and a few disappointments too!

5. In my own situation, both my maternal grandparents were of unknown origin due to an adoption, possible false names, no record of father's name, etc. DNA has enabled me to solve one of the mysteries and I have high hopes of resolving the other one day.

So a rough estimate of numbers and the real experience of many people shows that DNA is a great boon to genealogy. It doesn't solve everything of course, and it generally requires a lot of work to be done, but for many of us it is absolutely essential.

Ancestral Family Tree DNA Testing / Re: Size of DNA data bases
« on: Tuesday 06 March 18 10:24 GMT (UK)  »
Hi Jane,

Somewhere in the ftdna settings you can tweak the closeness of match.  I can't remember their exact terminology offhand, but you can limit matches to the equivalent of very close, medium or distant. 
You can use that searching in the chromosome browser (available only to paying customers), though I have never bothered. In the main match list, I don't think we need that because we can sort on relationship and so see all the closest matches first.

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