Why Y?

The part of the DNA that is tested for similarity is the Y-chromosome and only a male carries it. The Y-chromosome follows the family surname, so if a male’s last name is “Davis,” then, unless he was adopted or never took his biological Davis father’s name, the patterns of his Y-chromosome should match other male Davis Y-carriers on his line.

We are a unique brand of Davis. Our haplogroup is I-L160+ (I2a1b). A haplogroup is a group of DNA testing results that shows a matching series of mutations deriving from a common ancestor many thousands of years ago. It is the deep ancestry origins of the group.

A majority of Davis participants on the Davis Surname Project are of one haplogroup, R1b1b, which is a common haplogroup in Europe. But our William Davis line is coming up as I-L160 (I2a1b), which is less common among Davises.

On the Davis Surname Project , you can see how many more R1b1b participants there are compared to our subgroup. Our subgroup, the William Davis DNA Project, listed as “K87577,”  has a maroon banner, about the 13th group down.  Although the larger Davis Surname Project group is constantly growing, the William Davis DNA Project is currently the largest subgroup.

Resources on Genetic Genealogy

Read BlairDNA’s DNA101 for all about DNA, chromosomes, Dsy markers, TMCRA, time to most common recent ancestor, etc. – a simple explanation of a complex topic.

Read FTDNA’s tutorial on genetic genealogy: how to frame the question you want to solve with DNA, how to choose the correct person to test.

Read Charles Kerchner’s Genetics and Genealogy, an Introduction: the rewards and risks of DNA testing, Case studies, types of DNA and more.

Kerchner Surname Y-DNA project page: case studies, false negatives

Whit Athey’s Y-DNA haplogroup predictor

I Have the Results of My Genetic Genealogy Test, Now What? by Blaine T.  Bettinger, PhD

How Many Markers?

With a exact match of a 12-marker test, you know you’re related but not how long ago or where on the family tree chart. The more markers tested, the more refined is the test  “resolution.”  The more markers that match, the closer the relationship. A 12 or 25-marker test could be an exact match yet end up differing substantially when extended out to 67 markers.

We try to have everyone in the project test to 67 markers since it is the best test for refining sub-groups among related cousins in a family. The 67-marker test enables a better estimate of when the probable ancestor in common lived.

The more markers that match, the more probable that he lived more recently, as close as 2 to 4 generations ago with an exact 67/67 match.

The 67-marker test makes it easier to identify your most recent ancestor in common since we are more likely to have records for more recent relatives than those in the distant past.

FTDNA’s Probability Chart

Probability for Most Recent Common Ancestor (MRCA)

Number of matching markers

50% probability that the MRCA was no longer than this number of generations

90% probability that the MRCA was no longer than this number of generations

95% probability that the MRCA was no longer than this number of generations

10 of 10

16.5

56

72

11 of 12

17

39

47

12 of 12

7

23

29

23 of 25

11

23

27

24 of 25

7

16

20

25 of 25

3

10

13

35 of 37

6

12

14

36 of 37

4

8

10

37 of 37

2 to 3

5

7

65 of 67

6

12

14

66 of 67

4

8

9

67 of 67

2

4

6

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