It seems like everybody has an opinion about this. Some use 5 generations, some 8, and some 10. Relatively few people use more generations than this, perhaps because often pedigree software won't do more than this, or if it does it gets very slow.
So let's look at some data. These are some numbers I computed from pedigrees of several different dogs. One had very low inbreeding (< 5%), the others had significantly more. For each of these individuals, though, the way the computed COI changed with the number of generations of data used was different. One thing is clear - unless the level of inbreeding is very low, or the pedigree very shallow, using only 5 generations of pedigree data is likely to be extremely misleading.
In this figure, it's easy to see how far wrong you can go. One animal (pink) has a COI at 5 generations of about 6% (not bad); at 10 generations it is up to about 10% (still not so bad); but including 30 generations of data reveals that the true COI is about equal to what you would get from the mating of full siblings (25%).
So let's look at some data. These are some numbers I computed from pedigrees of several different dogs. One had very low inbreeding (< 5%), the others had significantly more. For each of these individuals, though, the way the computed COI changed with the number of generations of data used was different. One thing is clear - unless the level of inbreeding is very low, or the pedigree very shallow, using only 5 generations of pedigree data is likely to be extremely misleading.
In this figure, it's easy to see how far wrong you can go. One animal (pink) has a COI at 5 generations of about 6% (not bad); at 10 generations it is up to about 10% (still not so bad); but including 30 generations of data reveals that the true COI is about equal to what you would get from the mating of full siblings (25%).
The coefficient of inbreeding is the probability of a dog inheriting two copies of the same allele from an ancestor on both the dam and sire's side of the pedigree. It is also a prediction of a dog's genetic homozygosity.
If you're worried about the probability of producing puppies with a genetic disorder caused by a recessive mutation, there is a whopping difference between the relatively low risk of about 1 in about 20 (6% COI with 5 generations) and 1 in 4 (25% COI using 30 generations).
Does it matter how many generations you use when calculating COI? Yes. How many generations should you use? As many as you can.
If you're worried about the probability of producing puppies with a genetic disorder caused by a recessive mutation, there is a whopping difference between the relatively low risk of about 1 in about 20 (6% COI with 5 generations) and 1 in 4 (25% COI using 30 generations).
Does it matter how many generations you use when calculating COI? Yes. How many generations should you use? As many as you can.
