In recent months I have seen the community up in arms about COI’s, a lot of stress and confusion has been caused by this little value and here I will make a conscious effort to explain it so that everyone can understand. The formula for the Inbreeding Coefficient
was developed by Swell Wright in 1922 and it indicates the probability that any two alleles for any gene are alike by decent, in theory this value can range from 0 to 100%. The inbreeding coefficient is determined by the number and location of a common ancestor within the lineage.
Now you must understand the genetic contribution each ancestor makes: Parents
each parent contributes 50% of the genetic makeupGrandparents
each grandparent contributes 25% of the genetic makeupGreat Grandparents
each great grandparent contributes 12.5% of the genetic makeupGreat Great Grandparents
each great great grandparent contributes 6.25 % of the genetic makeup
This is where the primary focus in your pairing should be because the likelihood of a trait being inherited beyond this is so unlikely that you probably have better odds of being hit by lightning. With that said, we must also evaluate if there has been any potential genetic issues with the lines you are considering pairing as that will be the most important denominator when assessing the COI.
Many continuously ask why is it ok to breed a glider that is very inbred? And to give it a value we will use a glider with a 25% COI and most importantly why is the COI of the offspring 0% in some cases. Let me explain….because a glider is inbred it does NOT
mean it has a genetic defect and IF
it does, it does NOT
mean it is a dominant mutation. The inbred glider may or may not have health issues of it’s own, if these issues are dominant only one parent must carry the defect for it to manifest in the offspring, with a dominant mutation 50% of the offspring have the POSSIBLITY
of inheriting the defect. An example of such a defect would be a polydactyl (having an extra digit). When dealing with a recessive mutation BOTH
parents must carry the same defective gene in order for the offspring to inherit it. So you can take two very inbred gliders from completely different lines that don’t share any common ancestors and wind up with a COI of 0% because the offspring will only inherit one copy of the defects each parent may or may not carry, and you would need two copies to be present for a recessive defect to be inherited.
So we come to, what is an acceptable COI? And to that question I don’t have an answer that will apply across the board for every situation. I can tell you what I look for in my breeding COI’s and I can tell you why. All of the pairs I have produce offspring that are below or right at 3% COI within 10 generations. Though I rarely rely on a 10 generation COI because of the ancestral genetic contribution, and I feel a 5 generation COI will more accurately depict the genetic scenario. Now, why do I pair them that way? Because when starting off with a glider that has a very low COI there are more possibilities available when pairing these gliders to produce color. This in it self springs another issue, when you are working with a 0% COI that COI can ONLY
go up when pairing said glider back to produce color. This is perfectly OK
! You are NOT
hurting the lines by this in ANY
way. I have seen people hysterical because of a 3 or 4% COI, I have seen them tell others a pairing with a 2.5% should not be done. Why? I can tell you one thing unless you have several secret lines out there that I am not aware of you are going to wind up with COI’s higher than that. If you took the time to research the possibility a young healthy woman with no history of genetic illness has of having a child born with some form of a genetic defect, I assure you the possibilities are much higher than the standards we are trying to set for our gliders. If you stop and actually research our most inbred gliders and their offspring you will find that most of them are living a long healthy life with no signs of illness what so ever that can actually be directly linked with genetics. Sure there have been a few deaths in which a necropsy was not performed or was inconclusive but you will find this with anything. Yet other lines that don’t appear to be severely inbred have had some “questionable coincidences“.
In closing I hope this has helped some of you better understand COI’s and what they really represent to you as an owner and breeder
and that this will diminish some of the fear of the unknown .