Irish Roots

August 31st

John Grenham


Genealogists love shortcuts. You only need to spend a few hours in front of a microfilm reader to understand why. The most recent promise of escape from the drudgery of research comes from DNA testing.

First, a few misconceptions: genealogical DNA testing is fundamentally different from the kinds of tests used in criminal law. Nor does genealogical testing have anything in common with medical DNA diagnosis, except perhaps an interest in paternity.

There are two basic kinds of genealogical DNA test, one based on the Y-chromosome and one based on mitochondrial DNA. Only males possess a Y chromosome, and in most naming traditions the family surname follows the male line, so a Y-DNA test is used to establish paternal descent.

How this test works is relatively straightforward. A DNA sample (usually a simple swab of the inside of a cheek) is analysed, a series of points on the Y-chromosome are chosen and their composition identified. These points are sites where small mutations are known to have taken place. The closer the correspondences between all of these points in any two samples, the more closely related are the two individuals who supplied the samples. Because geneticists know the rates at which these small mutations occur, it is also possible to work out fairly precisely when the most recent common ancestor of the two individuals lived.

The implications are clear: Y-DNA testing tells you how closely youíre related to someone, not who your common ancestor was. In the majority of cases, the common ancestor lived before the start of record-keeping, so itís unlikely youíll ever be able to identify them.

Back to the microfilm reader, then. More on DNA next week.


Comments and suggestions are welcome, to irishrootsatirishtimes.com.

Current column

2014

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
6
3
3
7
5
2
7
13
10
10
14
12
9
14
20
17
17
21
19
16
21
27
24
24
28
26
23
 
 
31
 
 
30


2013

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
7
4
4
1
6
3
1
5
2
7
4
2
14
11
11
8
13
10
8
12
9
14
11
9
21
18
18
15
20
17
15
19
16
21
18
16
28
25
25
22
27
 
22
26
23
28
25
23
 
 
 
29
 
 
29
 
30

 
30


2012

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
2
6
5
2
7
4
2
6
3
1
5
3
9
13
12
9
14
11
9
13
10
8
12
10
16
20
19
16
21
18
16
20
17
15
19
17
23
27
26
23
28
25
23
27
24
22
26
24
30
 
 
30
 
 
30
 
 
29
 
31


2011

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
3
7
7
4
2
6
4
1
5
3
7
5
10
14
14
11
9
13
11
8
12
10
14
12
17
21
21
18
16
20
18
15
19
17
21
19
24
28
28
25
23
27
25
22
26
24
28
26
31
 
 
 
30
 
 
29
 
31
 
 


2010

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
4
1
1
5
3
7
5
2
6
4
1
6
11
8
8
12
10
14
12
9
13
11
8
13
18
15
15
19
17
21
19
16
20
18
15
20
25
22
22
26
25
28
26
23
27
25
22
27
 
 
 
 
31
 
 
30
 
 
29
 


2009

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
6
2
2
6
4
1
6
3
7
5
2
7
13
9
9
13
11
8
13
10
14
12
9
14
20
16
16
20
18
15
20
17
21
19
16
21
27
23
23
27
25
22
27
24
28
26
23
28
 
 
 
 
 
29
 
31
 
 
30