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The science of
paternity
The mother and father
each donate half of their DNA to their children. Of course, the
parents receive half from each of their parents, and so on. For now
we will focus on just parents and children.
In figure 1,
the mother has donated her red half to two of the children and her
yellow half to two. She could have, just as easily, donated yellow
to all four or red to all four. The same holds true for the father's
DNA. But we
don't look alike
How your child looks
may be
a poor indicator of paternity for many reasons but will still make you
question the relationship. If the child looks nothing like you or
has black hair when you have blond, it may be time for a DNA test
but don't be surprised if he/she is still your child based on the DNA
test. In figure 1, you can see from the illustration how two siblings can range
from very similar to nearly nothing in common, and still be from the
same parents. This is why a DNA test is so important.
My personal
barcode
Your DNA profile for
paternity is made up of numbers (also called alleles). These numbers represent the genetic
contribution passed down from each generation of parents. In figure
2, if we focus on 1 genetic location, you see the father and mother both have two numbers.
Each received one of the numbers from their mother and one from their father. Just as with the colors, there are four possible outcomes
for the children.
You can see that if the child's DNA type was a
[13,13] at this genetic location, it would not be possible for the man to be the father. It is
possible for two offspring to have the same two numbers if we only look at
one genetic location and for this reason we examine 16 different locations
or genetic systems.
A typical
father/child/mother comparison
|
Genetic System |
Alleged Father |
Child |
Mother |
|
D8S1179 |
14,15 |
12,14 |
12,14 |
|
D21S11 |
30.2,31.2 |
30.2,31 |
29,31 |
|
D7S820 |
10,11 |
10,11 |
9,10 |
|
CSF1PO |
11,12 |
11,12 |
10,11 |
|
D3S1358 |
15,18 |
15,18 |
15,16 |
|
TH01 |
6,9 |
9,9.3 |
7,9.3 |
|
D13S317 |
9,12 |
9,11 |
11,12 |
|
D16S539 |
11,13 |
11,11 |
11,13 |
|
D2S1338 |
17,25 |
17,24 |
22,24 |
|
D19S433 |
15,15 |
15,15 |
12,15 |
|
vWA |
16,18 |
15,18 |
15,16 |
|
TPOX |
11,11 |
8,11 |
8,10 |
|
D18S51 |
14,14 |
12,14 |
12,16 |
|
Amelogenin |
X,Y |
X,Y |
X,X |
|
D5S818 |
11,13 |
12,13 |
12,12 |
|
FGA |
18,24 |
18,22 |
22,23.2 |
Alleged father
excluded
|
Genetic System |
Mother |
Child |
Alleged Father |
|
D8S1179 |
12,13 |
13,13 |
12,13 |
|
D21S11 |
32.2,33.2 |
32.2,33.2 |
30,32.2 |
|
D7S820 |
12,12 |
10,12 |
11,11 |
|
CSF1PO |
11,11 |
10,11 |
11,14 |
|
D3S1358 |
14,18 |
14,16 |
16,17 |
|
TH01 |
7,9.3 |
7,9.3 |
6,9 |
|
D13S317 |
11,12 |
11,12 |
11,13 |
|
D16S539 |
12,13 |
11,12 |
12,13 |
|
D2S1338 |
19,20 |
17,20 |
17,23 |
|
D19S433 |
14,14 |
13,14 |
14,14 |
|
vWA |
14,16 |
16,17 |
15,16 |
|
TPOX |
10,11 |
8,10 |
8,8 |
|
D18S51 |
14,15 |
14,17 |
12,14 |
|
Amelogenin |
X,X |
X,Y |
X,Y |
|
D5S818 |
11,12 |
11,12 |
11,13 |
|
FGA |
21,21 |
21,25 |
21,21 |
|
 
   
Figure 1
Figure 2
 
Possible
Children
Child 1:
[10,13]
Child 2: [10,14]
Child 3: [12,13]
Child 4: [12,14]
In this
case, you can see that the mother and father have contributed
equally to the genetic profile of the child. The report would read
"the alleged father can not be excluded from being the biological
father and the probability of paternity is 99.99%".
You
notice the Amelogenin marker has letters instead of
numbers. This is because the Amelogenin marker indicates the sex of the
individual. XX is for female and XY is for male.
In this
case, the man who was tested as the alleged father is impossible to
be the biological father of this child. He does not share a number
(allele)
in common at each of the genetic systems tested.
Numbers
highlighted in red are DNA types that the alleged father could not
have donated to the child. The report would read "the alleged father
is excluded as the biological father of the child". Exclusions are
always confirmed by a complete second analysis.
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