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Why the Big Y Test?

Roberta Estes

My recent article about the Big Y test sale and coupons bundled with a free 111 marker upgrade at Family Tree DNA generated quite a number of questions about the Big Y DNA test itself, and why a male might want to take one. I’ll answer that question, along with a few more that have arisen, but the coupon sale I referenced only pertained to December 2017. The rest of this article is still very relevant!

Why the Big Y?

Y DNA tests test a man’s direct paternal (usually surname) line and fall into two groups.

The first group, STRs, are the typical 12, 25, 37, 67 and 111 Y DNA tests.  STR marker location values change rapidly, as compared to SNPs which mutates more slowly.

Each STR test tests the number of STR markers it’s named for. In other words, a 37 marker test tests 37 marker locations with the goal of matching other men with the same surname. Often, as you test higher levels, the results become much more specific and you “lose” matches to men with non-matching surnames. In this case, “losing” is a good thing, like weight!

The closer the STR match on more markers, the more reliable the results. Fewer matches generally mean we’re filtering out the more distant matches in time and the closer in time you shared a common ancestor with the people you match the most closely on the highest marker test you’ve both taken.

In other words, you might match 50 people at 37 markers, but only 20 at 67 markers and 4 at 111 markers.  Those 4 men are the most closely related to you on that direct paternal line – which is why we strongly suggest that people upgrade to 111 markers.

You can see in this example from the Estes project that the first two people whose surname is Estes are not biologically descended from the same male as the last four individuals – because their STR markers showing in the project are quite different.

Because STR markers mutate more rapidly, they are very useful for genealogy – and are used for that purpose.  An exact high marker match (typically 37, 67 or 111) to a male with the same surname indicates that you share a common ancestor with that man, probably within the past few generations and certainly since the advent of surnames. STR mutations sometimes happen independently in different lines, and when that happens, it’s called matching by convergence.

SNPs, on the other hand, are much more stable and mutate at a much slower rate and are therefore sometimes not as useful for traditional genealogy – BUT – they have the power to look further back in time where we have no tools other than DNA to make discoveries about our ancestors.

In general, but not always, men known to descend from a common ancestor will share the exact same “terminal SNP” – meaning the SNP mutation that happened the most recently.  Sometimes a SNP mutation will have happened in the past few generations and men who share a common ancestor since the advent of surnames will have a different terminal SNP, but not often and if they do, it’s generally only one step down the haplotree from each other. Just the “son” leaf on that branch.

On the Big Y haplotree, above, of an Estes male, five people match him on the BY490 branch, six on the BY482 branch above, and so forth. Of course, the next question is who matches him on these branches, so he will look at his Big Y match list to see those individuals.

What this means is that, in general, SNPs define more distant clan relationships, because they happen less often, and STRs define more recent surname relationships – although the more SNPs that are discovered – the more instances of some overlap we see.

The following chart shows where the two kinds of testing are the most useful – which illustrates why we need both kinds of testing.

Sometimes, there are no new SNP mutations that have occurred in a particular since the adoption of surnames. Of course, there is an exception to every guideline, and it just might be you. In fact, it could be between you and your father, or your father and his father. You don’t know what you don’t know and the only avenue to discovery is DNA testing.

What Does the Big Y Do?

While the STR panel tests specific addresses on the Y DNA to read a specific location – the Big Y test is a scan that scans the majority of the Y chromosome.

In other words, the 37 marker test provides you with results for 37 individual locations, or alleles, on the Y chromosome by measuring the number of repeats found at those locations specifically.

However, the more DNA addresses to be checked, the more expensive the test – which is why STR testing is broken into panels.

The Big Y test scans the majority of the Y chromosome to compare to a standard Y DNA pattern.  Because scan technology, known as NGS or next generation sequencing, allows us to look at tens of thousands of locations, it is not as accurate as looking at one specific location (think google satellite view versus driving down the street).  The DNA sequencing equipment scans the entire Y chromosome several times, like 25 or 30, and then reports on how many times something out of the ordinary is seen at a specific location.

If the scan spots something unusual 10 times or more, it’s called as a positive “result.”  Ten times or less, it’s considered a blip and not a high enough confidence result to consider as a valid result to report to a customer.

Why Do You Care?

As a customer, you may not care about the scans and underlying scientific processes that I just described – but you do care about the outcome which is your confirmed haplogroup closest in time to you on the tree. That information is important genealogically.

The Y DNA haplotree is the result of mutations that occurred every few hundred or few thousand years over the lifetime of mankind.  The mutation that identifies you the most closely with your closest male relatives is the last mutation that occurred that you all share – or don’t – which means a new mutation happened since the advent of your surname, assuming you do actually descend from a common ancestor and don’t just circumstantially carry the same surname. Yes, that does occasionally happen.

The result for the customer who takes the Big Y test is that the haplogroup predicted through STR testing is confirmed and generally several more branches and leaves are added to your own personal haplogroup tree.

Family Tree DNA very accurately predicts your branch haplogroup when you take an STR test, but it’s a major branch, near the tree, not a small branch and certainly not a leaf.  Smaller branches can’t be accurately predicted nor larger branches confirmed without SNP testing. The most effective way to SNP test for already discovered haplogroups – plus new ones never before found – perhaps unique to your line – is to take the Big Y.

While all of this science may not sound exciting at first glance, the results certainly can be, for a genealogist anyway.

The Big Y:

Together, STR and SNP tests provide us with the closest mutations meaning the most genealogically relevant as well as (generally) older and more distant mutations, giving us at least some information before the age of surnames. This means you will match men who adopted surnames about the same time your ancestors did.  If you are a McDonald, you might match men whose surname is Campbell, as an example. Or, you might match men with Scandinavian surnames.  All of these pieces of information add to the story of your ancestors before surnames and records – the point at which your paternal line is unquestionably lost to traditional genealogy. Big Y testing is a way to reach back behind that veil.

How else will you ever learn the history of your ancestor in that timeframe? And why wouldn’t you want to?

Summary

If you are interested in discovering any of this information, the Big Y is the most thorough avenue for the genealogist.  You can purchase some SNP markers individually, but that gets expensive very quickly, and you can’t learn about any new markers your DNA might hold if you purchase only SNP markers previously known to exist. Y DNA holds hundreds or even thousands of SNPs with mutations to report.

Additionally, many men’s DNA also holds never-before-discovered SNP mutations.  You can’t discover those any way other than a Big Y test.

Who Should Purchase the Big Y?

The Big Y is only an upgrade test. You can only see the Big Y as a purchase option on your account as an upgrade.  Click on the blue Upgrade button located in your Y DNA section or at the top right of your personal page.

Questions

Answer – Test your father or brother, or a male relative who carries your father’s surname and descends from the common male ancestor through the direct paternal line.  The article, Concepts – Who To Test For Your Father’s DNA will help you find a male to test for your father’s line.

Answer – Easy.  Just order the BIG Y-500 which includes the 111 marker test, the Big Y and additional free STR markers.

Answer – Just click on your blue Upgrade button.

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Disclosure

I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

Thank you so much.

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