What is the DNA Project?
By far, the majority of paternal lineage testing is done through Family Tree DNA (FTDNA), a genealogical DNA testing service designed to help you discover your family roots. Raw test data derives from genealogical tests purchased from FTDNA. FTDNA surname projects are administered by volunteer members of the project. The volunteer administrators perform data analysis, help to answer questions and interpret results for project members, and facilitate communication and collaboration among the members.
The intent of this webpage is to interpret Y-DNA test results from the FTDNA Curley surname project and other public sources in order to add value to the raw data through meaningful interpretation, as well as to serve as a general resource for Curley researchers. But the owner of this website is an independent researcher who has no formal affiliation with Family Tree DNA.
One goal of this project is to encourage more Curleys to participate in the DNA project in order to grow the database of Curley test subjects. The ultimate goal is to develop a comprehensive tree of the Curley surname and enable participants to figure out where they fit within the tree.
What is Genetic Genealogy?
Genetic genealogy is especially useful when traditional research methods have hit a brick wall. If you get a DNA match with someone who has a documented lineage to an earlier ancestor, this will tell you that you likely share some of the same ancestry.
If there is a gap in your documentation trail, DNA testing may help you cross that gap. If you have a suspected ancestor that you can't confirm through documentation, DNA testing may be able to confirm or refute your suspicion. Sometimes, there are multiple individuals in the documentation with similar names, birth dates, and locations. If you know that one of them is your ancestor, but haven't been able to establish which one, DNA testing may be able to identify the right one, or at least narrow down the list of possible candidates.
The good news is that the database will continue to grow over time. Even if you don't get an immediate match when you are tested, you may get additional matches later as new test subjects are added to the database. We are actively recruiting new participants, and as the cost of DNA testing continues to decline over time it can be expected that more and more Curleys will be tested.
Also keep in mind, even if you don't get a close DNA match to another Curley member, the test results can still be enlightening. The DNA comparison is not limited to the Curley surname only. There will also be more distant matches to testees with different surnames. The DNA test results sometimes reveal connections between surnames, possibly indicating a common ancestor prior to the establishment of surnames, or possibly indicating a genetic crossover between different surnames due to a marital infidelity or adoption somewhere in the lineage. Such matches between surnames can sometimes help identify clans or localities associated with a specific genetic group. So even if you don't get a close match to another Curley, DNA testing can still provide interesting insight into your ancestral origins.
Y-DNA Testing Explanation
The Y chromosome is carried by males only. Whereas most chromosomes are inherited from both father and mother, the Y chromosome is inherited solely from the father. For most chromosomes, the father's and mother's DNA combine in the offspring to create a new genetic pattern. So the genetic code will change from one generation to the next. But the Y chromosome is unique, being passed from father to son fully intact. It does not mix with the mother's DNA at all. So the pattern of the Y-DNA will be mostly unchanged from one generation to the next.
Within DNA, there are some places in which the same pattern is sequentially repeated multiple times. These copied segments are called "short tandem repeats", or STR's. The number of times that these patterns repeat varies from one individual to another. The number of repeats is usually the same for father and son. If the father happens to have 14 repeats, then the son will also have 14 repeats.
Y-DNA is usually passed from father to son intact, without being modified. But on rare occasions, there is a copying error in the DNA that is passed onto the son, so that the son will have a slightly different STR count than the father. For the STR markers used in genetic genealogy, such copying errors generally occur once in every few hundred times or so. So, if we are looking at 111 different STR markers (the highest level of Y-DNA testing available through FTDNA), we can expect there to be a change to an STR count about every 2 generations, on average.
At first thought, one might think that these copying mutations might make it impossible to track the DNA pattern through the paternal lineage, as the mutations keep accumulating over multiple generations. But it turns out that these mutations can be used to our advantage. Studies have determined how frequently mutations occur for each marker. This makes it possible to compare the STR markers between two related individuals, count the number of differences, and estimate how many generations worth of mutations separate the two individuals.
FTDNA has identified 111 of these repeating sequences, or "markers" that it uses for its genetic testing. By making a table of the number of repeats for each marker, one can compare the DNA of any two individuals to determine whether they share a paternal lineage. The raw STR test results for the Curley surname project may be viewed by clicking the "Y-DNA Data" tab at the top of this page.
The first row in the chart below contains the names of the STR markers used by FTDNA for the 37 marker test. The second and third rows list the numbers of times that each STR is repeated for two different test subjects.
Looking at the first 37 markers for kits numbers 176429 and 253019, one can see that the STR values are identical. These two project members are father and son, so this is what we should expect.
However if we compare 253019 with 266661, we can see quite a few differences in the STR values, which tells us that these two individuals are not closely related to each other.
The table below shows the STR test results, GD, MRCA, and TMRCA for two hypothetical test results.
On average, STR's mutate one time out of a few hundred. But different STR's mutate at different rates. FTDNA has deliberately chosen the STR markers that they use for their test. Some of the markers mutate especially quickly and others mutate relatively slowly. This allows the MRCA estimate to be calculated more accurately for a wide spectrum of time ranges.
The MRCA value is not an exact prediction that will nail down precisely how closely the individuals are related. It is just a statistical estimate, based on the knowledge of how likely it is that certain mutations will occur. Because of this, MRCA estimate is usually presented in the form of a plot or a table.
The peak of the plot gives an idea of how closely related two people may be, but as the example above shows, the possible range for a MRCA is actually much greater. It is possible for the common ancestor to be greater than or fewer than 10 generations distant. The numbers above or below the peak are just less likely. For example, it is possible for the common ancestor to be 5 generations removed, but this would only be the case in about 1.5% percent of all cases. Looking at this example, one can see that there is a significant chance for the MRCA to be anywhere from about 3 generations distant up to as many as 25 generations distant. The MRCA estimate is a useful indicator of how distant a shared ancestor is likely to be, but it does not precisely determine the exact number of generations.
The MRCA calculation is sometimes plotted based on "transmission events" rather than generations. Transmission events are simply the number of offspring in the lineage, each one having the opportunity for a Y-DNA mutation to occur. For example, if a grandfather has two grandsons through two different sons, then the two grandchildren are separated by 4 transmission events - one from the grandfather to his son and then another to his grandson, and the same thing again for the other branch. So the number of transmission events is simply double the number of generations. The sample chart below shows the same MRCA calculation as above, plotted in terms of transmission events rather than generations.
FTDNA presents the MRCA estimate in the form of a table. For each Y-DNA match, there is a TiP (Time Predictor) report available. This report presents the MRCA data as a tabulated list, with the cumulative probability listed for a range of generations. The example below shows the MRCA estimate for a GD of 5 out of 111 markers. In this case, the 50% line is just less than 6 generations. There is a 51% chance that the MRCA will be at 6 generations or fewer, and a 49% chance that the MRCA will be further than 6 generations. There is a 92% chance that the MRCA is within 11 generations or fewer. When investigating a possible common ancestor for this Y-DNA match, it would be wise to begin the search at 6 generations, and then expand the search outward in both directions from there.
The example below shows the MRCA estimate based on 37 markers and 111 markers. Both plots have the same amount of genetic distance as a percentage of markers tested, at 5.4% each. The 111 marker comparison narrows down the likely range for a common ancestor to roughly half the range of the 37 marker test. If a Y-DNA test indicates a common ancestor with another person, it is often useful to upgrade to a higher level of testing in order to narrow the estimated range of the common ancestor.
DNA Lineage Corruption
Because of corrupted genetic lineages, surname groups often have multiple genetic groupings, even if the surname has only a single documented progenitor. As a result of this fragmentation, a surname group will typically have around one half to two thirds of its members grouped into a few major lineages, with the remainder being genetic loners that don't match with any major lineage.
With the currently available test data, the Curley surname appears to be following this pattern. About two thirds of the test subjects fall into a few major groupings. The remainder have not yet found a DNA match to other Curleys.
Various Types of DNA Testing
Here's a brief explanation of the other kinds of testing available through FTDNA:
- MtDNA - This is a test of the maternal DNA that is passed down from the mother to her children. MtDNA is carried in the cellular mitochondria, unlike the more familiar nuclear DNA. MtDNA is passed from mother to child without experiencing any genetic recombination with the father's DNA. It can be used to identify the deep ancestral origins of your maternal lineage. Since the surname is inherited through the father, mtDNA testing is of no interest for researching surnames.
- Autosomal DNA - FTDNA's autosomal DNA test is called the "Family Finder" test. This is the same type of test that is offered by Ancestry.com and 23andMe. The autosomal DNA test utilizes DNA segments from multiple chromosomes, not just the male Y chromosome. Because of this, it can find matches through both the paternal and maternal lines. The drawback is that, because the DNA is recombined from both parents in each offspring, some of the genealogy markers get jumbled up and lost with each generation of offspring. So this test can only reliably find matches around 5 generations distant or so. Because of the limited time range of this test, it has minimal utility for surname research. However, if you get an autosomal test match through your paternal lineage to someone who has taken a Y-DNA test, then you can learn something of your own paternal lineage by association.
- SNP - FTDNA's more advanced testing options include SNP (single nucleotide polymorphism) testing. These tests check for a very specific mutation of a single location in the DNA. These tests divide the tree of humanity into finer and finer "subclades", or subdivisions, beyond what's possible with a standard test, helping determine relationships between surnames, clans, etc. Some SNPs are associated with specific locales or identifiable groups of people. For example, there's an SNP which is relatively unique to the province of Leinster, Ireland. If you have already taken a Y-DNA test and are interested in additional testing, you may wish to consult the project group administrator for a recommendation. A genetic genealogy expert may be able to predict what SNP mutations you are likely to possess, based on your pattern of STRs.
- Big Y - This is the ultimate Y-DNA test offered by FTDNA. This test will sequence a large fraction of your entire Y chromosome, providing a wealth of raw data. You will discover a large number of SNPs that are unique to yourself and your own family, and possibly find some that you share with a small group of your closely related branches. Discovering SNPs shared by small groups of people can hypothetically help you understand the origins and history of your lineage. However, the number of people who have taken this test is quite small. So the benefit of taking this test is currently limited, as you are not likely to identify any new genetic groups beyond what is already known from STR data. Over time as people continue to take this test and the database grows, the data from this advanced test may be very useful for understanding the history and origin of your paternal lineage.