Genetic Test for Maternity

Aug 31st, 2008 | By | Category: Featured Articles, Genetics, Lead Article

Well, we seem to have a bit of a question here.

If I were a woman accused of claiming my daughter’s child was my own, and I knew such accusations were false, I’d use science to prove myself right.

Using genetics to test for maternity is no different than in paternity testing, and I wrote about that a bit ago:

Paternity testing is all about mixing and matching.

DNA-based tests work by comparing the recipes—the alleles—you have for a given gene to those of a possible child. For most genes, we get two alleles—one from our mother and one from our father. A child of yours must have one of your alleles for all the paired genes in his or her DNA.

Well, how can we use this to figure out if a baby is from a woman or her daughter? Let’s look at the example for the pair of alleles for one gene:

(Click on the image for a larger version.)

In this example, I’ve assumed the most complicated combination–where everyone is heterozygous with distinct alleles. Since we know the relationship between the daughter and her parents, we must assume she received one allele from each parent. Therefore, we have six alleles, giving us 15 possible combinations. (Want to check my math? The formula is 6 choose 2.)

Try to follow the logic yourself. Of the fifteen possible babies, several definitively cannot be the mother’s child–as the baby doesn’t have an allele from the mother. Several are definitively not the daughter’s child (for the same reason.) A few combinations cannot be either of their child (mixup at the hospital)? Most are ambiguous–could be from either potential mother.

Well, how do we deal with the ambiguity? If you look at many genes at once (trivially easy to do with current technology), it become easy to rule out a potential mother.