HGG Community Forums

Fewer unique ancestors is bad for the inbreeding calculation.

Inbreeding, as far as I can tell, is calculated by looking at the total number of foundation ancestors and the total number of unique ancestors.

Declan has 15 unique foundation ancestors out of 60 total foundation ancestors. 15/60 = 25% unique foundation ancestors, which means 75% inbreeding.

Carnelia has 49 unique foundation ancestors out of 143 total foundation ancestors. 49/143 = 34% unique foundation ancestors, which means 66% inbreeding.

The inbreeding calculations are not guaranteed to be 100% accurate. I suspect they don't count foundation ancestors that are too far back to appear in the extended pedigree. Because Declan should have MORE foundation ancestors than Carnelia. It would make sense to me that Declan should have 2 more foundation ancestors than Carnelia since his sire has only 2 foundation ancestors.
You'll notice at the end of their pedigrees some of their foundation ancestors have little [+] signs next to their names. That means there are more ancestors further back that aren't showing up in the pedigree. I am guessing what happened with Declan is that a big chunk of Carnelia's foundation ancestors are far enough back in the pedigree that they dropped off of Declan's extended pedigree and resulted in the number of foundation ancestors being counted for his inbreeding calculation as being smaller.

If you wanted to be really ambitious you could run back all of the + signs and build out a totally complete family tree for each of them and hand calculate the number of foundation ancestors, and the number of unique foundation ancestors and come up with a true inbreeding calculation.

Thank you all for the thoughtful answers.