A Brief Discussion of CHASE / CHACE Paternal DNA Test

 

I.  INTRODUCTION

 

The following discussions make some necessary simplifications so that things don’t get too technical. 

 

First, let’s review what the individual tests show, why there are differences in some of the sets of numbers displayed for each person, and what these differences mean.

 

The individual test results displayed in the table show the values of each person’s DNA for a set of Y chromosome genetic “markers” (DYS ID#) that are used by FamilyTreeDNA Inc. for establishing probable ancestral connections between MALE individuals.  Basically, the better the “match” between individuals, the higher the probability that they have a common ancestor, and the more recent that common ancestor might be, although it’s not quite as cut and dried as that. As we shall see in a moment, both the number of markers included in the test, and the differences between them for any two individuals have a great bearing on the practical usefulness of the results in establishing a common ancestor.

 

It is important to understand up front that these tests cannot identify who a common ancestor might be. But they can serve to suggest which individuals probably do (or do not) have a “recent” common ancestor, and help prove or disprove other information that may point to him. And we say “him” because these tests are for genetic values of the Y chromosome, which is passed down only through the male line of a family.

The values of these genetic markers change (mutate) slowly over generations, which is why individuals even with a relatively recent common ancestor can have slightly different values for one or more of them. Since the genetic mutations of any given marker are random (that is, they don’t happen with predictable regularity between generations), we cannot predict exactly how often they occur. However, geneticists have been able to calculate the mean probability that a mutation will occur in any one generation, and this provides a way to estimate the time back to a “most recent common ancestor” (MRCA) based on the number of observed mutations (that is, the number and size of differences in the values of the markers tested) by which the Y chromosomes from two individuals differ.  As one includes more and more markers in the test, the probability distribution becomes tighter and tighter about its mean value, and estimates of the number of generations back to a MRCA have higher precision. 

But since the estimates are based on probabilities, there are no absolute certainties.  This is especially important when comparing individuals using only 12 marker test results.  In this case, even a “perfect” 12 out of 12 match between two individuals cannot, by itself, be interpreted to mean the two definitely have a “recent” common ancestor. Other genealogic evidence is required to validate this determination. 

 

  II. INTERPRETATION OF CHASE/CHACE DNA TEST RESULTS

 

1.     Aquila line descendants (Light blue on the chart)

Six of the DNA test participants have identified their ancestry back to Aquila through records.  The almost perfect match (only a 1 step difference in one marker for each) between the three who took the 25 marker test  (Richard, Russell and Lonnie) strongly suggests that a recent common ancestor within the last 7 or so generations can be reasonably inferred at the 50% probability level (or within 23 generations at the 90% level).  This would be consistent with Aquila as a common ancestor in as much as he is about 10 generations removed from them.  The 12-marker test result showing only a one step or no difference can be presumed to confirm the Aquila lineage of the other four whose research indicated that ancestry.

 

Three participants who have been unable to identify their ancestry line had a 37 marker test done. The very close 25 marker match (only a 1 step difference in one marker) with the three participants who have identified their Aquila ancestry through documentation makes it highly probable that they descend from Aquila (or Thomas, since both would have the same DNA).

 

Two participants who are uncertain of their ancestry had a 12 marker test done with results that match those of known Aquila descendants. While this indicates a possible Aquila lineage, confirmation by genealogical research is required establish such a relationship.

 

 

2.     William line descendants (Yellow on the chart)

A William ancestry has been established through research of records by seven participants, and their identical 12 or 25 marker tests confirm a probable MRCA within the last 14 generations (50% probability level), consistent with their prior research.  The matches of 25-marker tests for other participants in the Yellow section (none of whom have traced their lineage back to an American progenitor) with those of the known William descendants provide a very high probability that they, also, are William descendants.  (Before being tested one of these individuals assumed he was descended from Aquila, but the DNA results very conclusively indicate otherwise.)  The one participant with an exact 12 marker match may be a William descendant, but other proof is required as discussed above.

3.     Other Chase Family Lines (Light green on the chart)

Both #8797 Laurence Chase, who has traced his ancestry to an 18^th century Samuel Chase in Bedfordshire, England, and #11634, Andrew Chase, who lives in England, have indicated they have some unspecified ancestral tie to the Chesham Chase line. However, the large number of mismatches between the two suggests that no common ancestor is likely within many, many generations.

Of perhaps more interest is the lack of any even reasonably close match between the 25 marker tests of either Laurence or Andrew and those of the known Aquila descendants.  The magnitude of the differences between them strongly suggests no recent common ancestor between either Laurence or Andrew and Aquila. Therefore, if either Lawrence or Andrew is, in fact, descended from the Chesham Chase line, then it is very unlikely that Aquila’s direct lineage is also from that line. However, no firm conclusion can yet be drawn since, as stated above, we have not yet received information to be able to identify and verify a specific link for either.
 

#6754 George G., a non-Chase surname who has been unable to trace his ancestry. While there are some similarities with the dna of known Aquila descendants, the number of differences in the 25 marker results make it unlikely that if there is in fact a common ancestor, he probably is not within many dozen generations.

Keith Hume’s only known link to the Chase line is maternal. His DNA results are included as an example of another surname line.  While it appears to be similar to the Aquila results, a 3-step difference in a 12-marker test translates to a high probability of no common (male line) ancestor within hundreds of generations.

Updated August 2009
RAC

 

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