The Paw Print Genetics Blog

Why is a Dam’s Sample Needed for Parentage Testing?

Why is a Dam’s Sample Needed for Parentage Testing?
Example for marker “A”: Pup is 1,3, Mother is 1,1 and Father is 2,3. The pup inherited allele 1 from the mother and allele 3 from the father.

At Paw Print Genetics, we are often asked this question: “Why do I need to send in a sample on the dam if I just want to know the father of my pups?”. The simple answer is because we need to compare the DNA of the pup to both parents in order to confidently confirm or exclude a potential sire.  Here is an example that helps explain why we need both parents for parentage testing. Keep in mind that a pup receives half of its DNA from its mom and half of its DNA from its dad, so for every marker that we examine, the pup has one allele (gene copy) from mom and one allele (gene copy) from dad.

For parentage (paternity) testing, we use a set of 99 informative markers to confirm or exclude a potential sire. For each marker, we get two results because the pup has two sets of DNA, one from the mom and one from the dad. The two alleles are each assigned a number based on their DNA sequence.  For example, for marker “A”, the pup might be 1,3; one allele has sequence 1 and the other allele has a sequence that’s been designated as 3.  If the mother is 1,1 at marker A and the father is 2,3, at marker A, then we know that the 1 came from the mom because she only has alleles that have the 1 sequence and the 3 came from the father because he has alleles 2 and 3.  If we based the parentage only on this single marker, we would conclude that the sire is the father.

However, what if we didn’t use the dam’s sample?  In another example, if the pup was 1,3 at marker B and the father was 2,3 at marker B, and the mom was not included in the testing, we don’t know if the 1 in the pup came from the mom or if the 3 in the pup came from the mom. We can’t assume that just because the father has a 3 allele that the 3 allele in the pup came from the dad.  If we use the mom in the analysis and find out that mom is 3,3, then she can only contribute a 3 allele to her pup, so the 1 allele must have come from the dad. Thus, a potential sire that has alleles 2,3 cannot be the dad in this case.

For each of the 99 markers in our parentage set, we compare the pup’s alleles to both of the parents’ alleles. Assigning the mom’s allele allows us to confidently include or exclude the sire’s contribution to the pup. Because we are examining so many markers, we are also able to distinguish fathers from sons, and brothers from one another. So if the two potential sires are highly related (first degree relatives), we are usually able to distinguish them from one another. If we are unable to do this, we have an additional set of 45 markers that we can use to further assess the parentage to confirm or exclude the sire(s).

Paw Print Genetics is a full-service genetic testing laboratory offering genetic testing for diseases, coat colors, traits and parentage. If you have any questions about parentage testing, please contact Paw Print Genetics at AskUs@pawprintgenetics.com or call toll free, 1-855-202-4889.

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