mDNA Analysis Cannot Give You a COI

A Facebook friend was told by Embark Veterinary that a Mastiff and Greyhound cross had a COI of 2% based a few overlapping segments of mDNA.

No, that dog does not have a COI of 2%. Embark is entirely wrong.

COI stand for "Coeffcieint of Inbreeding" and it is a mathematical construct, developed by Sewell Wright, based on pedigree.

Embark was not using pedigree, but mDNA which is far from the same thing as the video, at top, suggests. Small segments of mDNA overlap are NOT how you calculate COI.

So what's the story?  It's not complex.  Dogs have not been around very long; maybe 40,000 years with very, very small, but continuous, shots of wolf.

Breeds, as we know them today, are only 150 years old, and most types are only about 600 years old. The oldest type (greyhounds) is perhaps 6,000 years old.

Greyhound mDNA is going to show up in the background of almost every mid-sized to large dog as it’s in the root stock of so many breeds.

But is a tiny scrap of vestigial mDNA the same as inbreeding?

Nope.

To be clear, Coefficient of Inbreeding is not a perfect metric.

If you have only 30 dogs, close the gene pool, and breed forward from there for 100 years, resulting in a pool of 250 dogs, a 5-generation pedigree will obscure the amount of true inbreeding.

But if you do the same thing over 150 years, with a breed pool that ends up with over 200,000 dogs, that 5-generation COI number is going to be a bit more useful. Why? Because with greater population size you get both more genetic drift AND you also get more folks slipping in dogs from other lineages (i.e. faking pedigrees). Faked or contrived pedigrees are terrific as they enter a lot of genetic wobble into the mix.  In fact, they are why puppy mill Scottie’s are healthier than those produced by so-called “good breeders”.

The fact that science can show that a few short scraps of MDNA are common to both a sire and a dam does NOT mean that any meaningful level of inbreeding has occurred, and it certainly cannot give you a COI.