Hi! I'm writing a character with a shady father and half-siblings. If he tested his own DNA against a collected sample, would the test be able to differentiate between whether that sample came from his father or his half-brother? I know that you can tell the difference between a parent and a full sibling, but since you only share half of your DNA with a half-sibling, I wasn't sure if that changed things. (It would be super helpful if you couldn't tell, plot-wise, but science comes first) Thanks!
Hi there! You happened to hit the nail on the head of the exact types of question I answer every day at work :)
Yes, you would definitely be able to tell who it came from, and the degree of the relationship that they have.
When we do parentage analysis, we aren’t generally looking at the whole DNA sequence (genome). Instead, we are looking at specific parentage markers. There are two basic tests that do this- microsatellite and SNP tests. They use different technologies, but the end result is the same.
For your story, the relationship between two half siblings is actually much weaker than a parent child relationship- parents give ~50% of their DNA to their children, which means that half siblings share ~25% of their DNA.
The biggest limit of parentage testing is actually the direction. If you give me two samples, I could tell you how strongly they are related (whether they are siblings, parent-child, grandparent-grandchild, etc.). But I can’t tell you which is which. So that means if blindly test a father and son sample, I could tell you that one is the parent of the other, but I couldn’t tell you which one is the parent, unless I have the second parent sample present. The other way to trick a parentage test is to submit a parent’s or child’s twin as the actual parent/child. Twins share 100% of their DNA, so, as far as the test is concerned, these two samples are identical!
So, unfortunately, not helpful to you plot-wise, but hopefully that does open up some possibilities for you! Thanks for asking your question!
