DNA Molecule

Cheek/Chick DNA Project

Genetic Distance

"Genetic distance" is the number of mutation "steps" or mismatches between any two individuals.  "0" is a perfect match, "1" is a one-step mutation, etc.  The more mutations, the longer the probable time period since the most recent common ancestor.  For purposes of genealogy, we are mainly interested in knowing whether we are descended from a common ancestor in a "genealogical timeframe" (usually 300 to 500 years).  Knowing that we had a common ancestor 2,000 or 5,000 years ago may be interesting, but it's not helpful for genealogy because no records exist that can pinpoint any particular ancestor.

Generally speaking, a genetic distance of 0, 1, or 2 on a 25-marker test, in people with the same surname, is considered a "match," with a high probability of a common male-line ancestor in the last 300 years.  A genetic distance of 5 or greater indicates that the individuals did not have a common male-line ancestor within a genealogical time frame.  A genetic distance of 3 or 4 on a 25-marker test is inconclusive: the individuals could be descended from a common ancestor in less than 300 years, but there needs to be additional evidence to establish the connection.

Important points to keep in mind:

Sample genetic distance from most typical
CHEEK FAMILY GROUP 1 Profile (25 Markers)
No. Ancestor Group Genetic
Distance
(25 markers)
Probability of Common Ancestor
200 yrs 300 yrs 500 yrs
2 William Cheek, Madison Co., GA 1 0 85% 94% 99%
7 James Chick, Knox Co., KY 1 57% 78% 95%
1 Richard Cheek, Alleghany Co., NC 1 59% 79% 95%
8 William Cheek, Madison Co., GA 1 55% 76% 94%
4 William B. Cheek, Buncombe Co., NC 2 28% 50% 81%
24 John Cheek, Carroll Co., MS 2 12% 31% 67%
18 William Chicke, Somerset, England 1? 4 3% 12% 42%
30 Henry Cheek, Adair Co., KY 2 9 0.8% 4% 23%
21 William Cheek, Carter Co., KY 10 0.2% 1% 10%
31 Nicholas Cheek, Shelby Co., KY 10 0.2% 1% 10%
41 John Wilbur Cheeks, Wilkes Co., NC Unique 7 0.1% 1.1% 9.8%
9 William Cheek, Jasper Co., GA 10 0.0% 0.2% 3.3%
26 Jesse Cheek, Maury Co., TN 9 0.0% 0.0% 3.0%
3 Elisha Cheek, Franklin Co., GA 13 0.0% 0.0% 0.2%
42 William P. Cheek, Bedford Co., VA 11 0.0% 0.0% 0.0%
10 Thomas R. Cheek, Franklin Co., GA 26 0.0% 0.0% 0.0%
36 James Cheek, Decatur Co., IN 3 29 0.0% 0.0% 0.0%

The 37-marker test allows for a more accurate comparison in borderline cases.  For example, Participant #24 matches the most typical Group 1 profile on 21 out of 25 markers, a genetic distance of "3."  This means that the probability of a common ancestor within 300 years is only 31%.  However, when 37 markers are tested, the probability goes up to 80%, making us pretty confident that Participant #24 is part of Family Group 1.

On the other hand, the difference between Family Groups 1 and 2 increases significantly when 37 markers are tested.  Based on the 25-marker test, there is a 23% chance that Participant #30 shared a common ancestor with Family Group 1 during the last 500 years.  Based on the 37-marker test, the probability drops to a miniscule 4.9%.

Sample genetic distance from most typical
CHEEK FAMILY GROUP 1 Profile (37 Markers)
No. Ancestor Group Genetic
Distance
(37 markers)
Probability of Common Ancestor
200 yrs 300 yrs 500 yrs
15 John R. Cheek, AL & TX 1 0 97% 99.6% 99.9%
25 Washington R. Cheek, Red River Co., TX 1 89% 97% 99.9%
38 Willis Cheek, Laurens, SC 1 89% 97% 99.9%
20 John Cheek, Carroll Co., MS 1 89% 97% 99.8%
7 James Chick, Knox Co., TN 1 89% 97% 99.8%
1 Richard Cheek, Alleghany Co., NC 2 73% 92% 99.4%
29 Jeremiah Cheek, Bedford Co., TN 2 72% 91% 99.4%
32 William Chick, Hanover Co., VA 2 70% 90% 99.2%
24 John Cheek, Carroll Co., MS 3 51% 80% 97.8%
44 Robert Cheek, Orange Co., NC 3 48% 77% 97.3%
18 William Chicke, Somerset, England 1? 7 1% 9% 46%
30 Henry Cheek, Adair Co., KY 2 16 0.0% 0.1% 4.9%
21 William Cheek, Carter Co., KY 16 0.0% 0.1% 4.9%
16 John R. Cheek, AL & TX Unique 16 0.0% 0.0% 0.1%
35 William Cheek, Surry Co., NC 18 0.0% 0.0% 0.1%
43 Austin Cheek, Culpeper Co., VA 3 42 0.0% 0.0% 0.0%


Note how the results differ when we use Family Group 2 as the standard for comparison:

Sample genetic distance from most typical
CHEEK FAMILY GROUP 2 Profile (25 Markers)
No. Ancestor Group Genetic
Distance
(25 markers)
Probability of Common Ancestor
200 yrs 300 yrs 500 yrs
21 William Cheek, Carter Co., KY 2 0 85% 94% 99%
31 Nicholas Cheek, Shelby Co., KY 0 85% 94% 99%
30 Henry Cheek, Adair Co., KY 1 58% 78% 95%
2 William Cheek, Madison Co., GA 1 10 0.2% 1.2% 10%
1 Richard Cheek, Alleghany Co., NC 1 11 0.0% 0.3% 4.2%
18 William Chicke, Somerset, England 1? 12 0.0% 0.3% 3.8%
9 William Cheek, Jasper Co., GA Unique 10 0.0% 0.2% 3.3%
8 William Cheek, Madison Co., GA 1 11 0.0% 0.2% 2.7%
26 Jesse Cheek, Maury Co., TN Unique 9 0.0% 0.0% 0.8%
41 John Wilbur Cheeks, Wilkes Co., NC Unique 10 0.0% 0.0% 0.2%
3 Elisha Cheek, Franklin Co., GA Unique 13 0.0% 0.0% 0.2%
10 Thomas R. Cheek, Franklin Co., GA Unique 26 0.0% 0.0% 0.0%
42 William P. Cheek, Bedford Co., VA Unique 29 0.0% 0.0% 0.0%
36 James Cheek, Decatur Co., IN 3 29 0.0% 0.0% 0.0%

 

Top