What is the coefficient of inbreeding (COI) and why does it matter?

This week you get just me (Jessica Perry Hekman) talking at you! I'm talking about the coefficient of inbreeding (COI), a measurement of genetic diversity that's commonly mentioned in discussions of individual and breed health. I talk about what it is, how to interpret it, how to get the measurement done for your own dog(s), why we care about it, and give the take-home messages from some papers with evidence for its importance in dog specifically. COI is not the only thing you should be breeding for, and it's rarely even the most important thing - but it's something we should keep in mind when we are working in closed gene pools.
NOTE: Oops, I said in the episode that the MDR1 mutation is recessive. It's not - it's incompletely dominant, meaning that dogs can be affected even with only one copy of the mutant allele. I apologize - please note the mistake as the correct information is important here.
I mention some previous podcast episodes with related material - you can find them here:
Alison Skipper, PhD on the history of breed registries: https://functionalbreeding.podbean.com/e/alison-skipper-phd-the-history-of-breed-registries/
Mary Peaslee, MD, MPH, on breeding for population health: https://functionalbreeding.org/breeding-for-population-health/

The papers:
https://functionalbreeding.org/the-impact-of-inbreeding-on-litter-size/ - Chu ET, Simpson MJ, Diehl K, Page RL, Sams AJ, Boyko AR. Inbreeding depression causes reduced fecundity in Golden Retrievers. Mammalian Genome. 2019 Jun 1;30(5):166-72. - "The least inbred dogs had an average litter size of 8 puppies, while the most inbred dogs had an average litter size of 6-7 puppies. On average, with each 10% increase in inbreeding, the litter size decreased by one puppy."
https://functionalbreeding.org/inbreeding-depression-and-lifespan/ - Yordy J, Kraus C, Hayward JJ, White ME, Shannon LM, Creevy KE, Promislow DEL, Boyko AR. Body size, inbreeding, and lifespan in domestic dogs. Conserv Genet. 2020 Feb;21(1):137-148. - mixed breed live on average 1.2 years longer than size matched purebreds
https://www.sciencedirect.com/science/article/abs/pii/S1090023313004486 - O'Neill DG, Church DB, McGreevy PD, Thomson PC, Brodbelt DC. Longevity and mortality of owned dogs in England. Vet J. 2013 Dec;198(3):638-43. doi: 10.1016/j.tvjl.2013.09.020 - again, mixed breed live on average 1.2 years longer than size matched purebreds
https://link.springer.com/article/10.1186/s40575-020-00086-8 - Urfer SR, Kaeberlein M, Promislow DEL, Creevy KE. Lifespan of companion dogs seen in three independent primary care veterinary clinics in the United States. Canine Med Genet. 2020 Jun 16;7:7. -   breeds with lower COI have 3-6 month longer expected lifespans
https://functionalbreeding.org/size-genetic-diversity-lifespan/ - Kraus C, Snyder-Mackler N, Promislow DEL. How size and genetic diversity shape lifespan across breeds of purebred dogs. Geroscience. 2023 Apr;45(2):627-643. - + 1% heterozygosity -> + 31 days of life
https://functionalbreeding.org/the-effect-of-inbreeding-body-size-and-morphology-on-health-in-dog-breeds/ - Bannasch, D., Famula, T., Donner, J. et al. The effect of inbreeding, body size and morphology on health in dog breeds. Canine Genet Epidemiol 8, 12 (2021). - 30kg dog: 0->40% COI -> 10% increase in veterinary care visits; 5kg or 60kg: 37% increase
https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007361 - Donner, Jonas, et al. "Frequency and distribution of 152 genetic disease variants in over 100,000 mixed breed and purebred dogs." PLoS genetics 14.4 (2018): e1007361. - purebred more likely to be affected, mutts to be just carriers