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A Brief Analysis of CHASE/CHACE DNA Test Results
I. INTRODUCTION
The following discussions make some necessary simplifications so that things don’t get too technical. For anyone who might want to read a more comprehensive explanation of how all this all works, go to http://nitro.biosci.arizona.edu/ftdna/TMRCA.html
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 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 a common ancestor. 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 can and do 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 every x 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 uses more and more markers, 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 keep in mind that 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 cannot, by itself, be interpreted to mean the two definitely have a recent common ancestor. Other evidence is required to validate this determination. In a study of 1386 DNA test participants representing 66 surnames, 971 individuals were found to share a unique 12-marker combination, but half of these shared it with someone with a different surname! And over 10% of the participants who had an exact match with another individual in the 12 marker test had a match of less than a 23 out of 25 in the 25 marker test, strongly suggesting that any common ancestor was many, many generations in the dim and distant past.
II. INTERPRETATION OF CHASE/CHACE TEST RESULTS
1.Aquila line descendants
Four of the test participants (Dick, Lonnie, Matthew & Robert) had identified their ancestry back to Aquila through records prior to the DNA test. Since Lonnie’s two one step differences from Dick are each in a “red” marker (see note at the foot of the chart), the 25 marker results for the two may be considered to be nearly identical, and 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 the two. Matthew’s 12-marker test result showing only a one step difference can be presumed to confirm his Aquila lineage also.
Participants #7463 & #30590 were apparently unsure of their Chase ancestry prior to an identified relative c1790. However, their exact 12-marker match with Dick would seem to reasonably suggest they likely lineage to either Aquila or Thomas—if, in fact, the two were brothers—but there is no way to tell which based on these tests.
2.William line descendants
A William ancestry has been established by records by four participants (Frank, Jim, Ray, Fred), and their identical 12-marker tests would seem to confirm a MRCA within the last 14 generations (50% probability level), consistent with their prior research. The identical matches of 12- and 25-marker tests (Rex’s single step mutation being in a “red” marker) for the four others shown in the Yellow section (none of whom could trace their lineage back to an American progenitor) provide a very high probability that they, also, are William descendants. (Before being tested one of these assumed he was descended from Aquila, but the DNA results serve to prove otherwise.)
3.Unknown line
#8797 Laurence Chase has traced his ancestry to an 18th century Samuel Chase in Bedfordshire, England, with a possible (unverified) tie to the Chase family in Chesham. While the hope was that DNA results might show a tie between his line and Aquila (thus providing evidence of a tie between Aquila and an identifiable English Chase family), the 9 and 7 step mismatch between the 25-marker tests of Laurence and the two known Aquila descendants (Dick and Lonnie) makes the probability very high that there was no common ancestor within the last thousand years or so.
4.Potential linkage with Chase line – non-Chase surname
#6754 George V., a non-Chase surname who has been unable to trace his ancestry, is a 12 marker match with Lonnie, suggesting a possible link in his male lineage to a male Chase in the Aquila line. The 25 marker results are not as clear, however, there being three one step differences from Lonnie, and four from Dick, although only one of them is in a non-red marker. Given the circumstances, one cannot draw any conclusions, except to note that if there is a common male ancestor, he probably is not within the last two dozen (or so) generations.
5.Keith Hume’s link to the Chase line is maternal. His DNA results are included only 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.
I. INTRODUCTION
The following discussions make some necessary simplifications so that things don’t get too technical. For anyone who might want to read a more comprehensive explanation of how all this all works, go to http://nitro.biosci.arizona.edu/ftdna/TMRCA.html
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 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 a common ancestor. 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 can and do 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 every x 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 uses more and more markers, 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 keep in mind that 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 cannot, by itself, be interpreted to mean the two definitely have a recent common ancestor. Other evidence is required to validate this determination. In a study of 1386 DNA test participants representing 66 surnames, 971 individuals were found to share a unique 12-marker combination, but half of these shared it with someone with a different surname! And over 10% of the participants who had an exact match with another individual in the 12 marker test had a match of less than a 23 out of 25 in the 25 marker test, strongly suggesting that any common ancestor was many, many generations in the dim and distant past.
II. INTERPRETATION OF CHASE/CHACE TEST RESULTS
1.Aquila line descendants
Four of the test participants (Dick, Lonnie, Matthew & Robert) had identified their ancestry back to Aquila through records prior to the DNA test. Since Lonnie’s two one step differences from Dick are each in a “red” marker (see note at the foot of the chart), the 25 marker results for the two may be considered to be nearly identical, and 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 the two. Matthew’s 12-marker test result showing only a one step difference can be presumed to confirm his Aquila lineage also.
Participants #7463 & #30590 were apparently unsure of their Chase ancestry prior to an identified relative c1790. However, their exact 12-marker match with Dick would seem to reasonably suggest they likely lineage to either Aquila or Thomas—if, in fact, the two were brothers—but there is no way to tell which based on these tests.
2.William line descendants
A William ancestry has been established by records by four participants (Frank, Jim, Ray, Fred), and their identical 12-marker tests would seem to confirm a MRCA within the last 14 generations (50% probability level), consistent with their prior research. The identical matches of 12- and 25-marker tests (Rex’s single step mutation being in a “red” marker) for the four others shown in the Yellow section (none of whom could trace their lineage back to an American progenitor) provide a very high probability that they, also, are William descendants. (Before being tested one of these assumed he was descended from Aquila, but the DNA results serve to prove otherwise.)
3.Unknown line
#8797 Laurence Chase has traced his ancestry to an 18th century Samuel Chase in Bedfordshire, England, with a possible (unverified) tie to the Chase family in Chesham. While the hope was that DNA results might show a tie between his line and Aquila (thus providing evidence of a tie between Aquila and an identifiable English Chase family), the 9 and 7 step mismatch between the 25-marker tests of Laurence and the two known Aquila descendants (Dick and Lonnie) makes the probability very high that there was no common ancestor within the last thousand years or so.
4.Potential linkage with Chase line – non-Chase surname
#6754 George V., a non-Chase surname who has been unable to trace his ancestry, is a 12 marker match with Lonnie, suggesting a possible link in his male lineage to a male Chase in the Aquila line. The 25 marker results are not as clear, however, there being three one step differences from Lonnie, and four from Dick, although only one of them is in a non-red marker. Given the circumstances, one cannot draw any conclusions, except to note that if there is a common male ancestor, he probably is not within the last two dozen (or so) generations.
5.Keith Hume’s link to the Chase line is maternal. His DNA results are included only 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.