STEP 4: COMPARING “BAR CODES”
We now have genotypes for a mom and her baby, and also all the
males that are potential fathers. We know that at every microsatellite
locus, the baby must have one allele copy that matches mom’s and
one allele copy that comes from dad. So now finding the father is as
simple as a matching game: at every microsatellite locus, we compare
the genotypes of mom, baby, and the potential dads. Remember our microsatellite
example, where there are 3 possible allele sizes (8, 12, and 16 base
pairs)? Let’s say the baby is (8,12) at that locus and the mom
is (12,16). And let’s say there are 2 possible fathers: candidate
1 is (8,16) and candidate 2 is (12,16). We know that the baby’s
12 had to come from the mother because that is the only allele they share. That
means the 8 allele had to come from the father. Candidate 2 does share
the 12 allele with the baby, but we know that had to come from mom.
Candidate 2 is excluded because it does not share the 8 allele with
the baby, while candidate 1 does. Therefore candidate 1 is the likely
father. A process similar to this is repeated across all the microsatellite
loci - we have a computer program that helps us do this much faster than we could by hand -
and eventually what should happen is that only one candidate male remains without any
exclusions with the baby. This means that only he could have given the second allele paired
with the mother's at every locus, telling us that he is the father.
So there you have it – now do you believe that you can go from
poop to paternity? Poop is jokingly referred to as “liquid gold”
by researchers because it is packed full of useful information! Not
only can we get DNA to use for paternity testing and population genetics
analyses, but we can isolate RNA and antibodies to monitor disease
and immunity and hormones to assess things like stress and reproduction.
And this is just the short list…
To read more about how researchers are utilizing this information read
Emily Wroblewski’s
research description.
