There are 3 main issues with inbreeding...
- Recessive genes get reinforced.
- First generation have a reduced fertility.
- Immune systems are weaker generally due to genetic similarity, meaning that if 1 person lack an immunity most others will too.
So lets talk about these 3 things...
2 is not a problem, because 2 actually is a screening mechanism that prevents completely broke dna to breed.
3 just means that the probability of getting sick from one disease vs another is higher than someone in the general populace's. That is to say that if someone has a 1/100 chance to catch something in general populace, someone from the inbred line might have a 1/90 chance to catch something.
1 is the misunderstood one... In the most basic of terms you have dominant(D) alleles and recessive(d) alleles. There can be multiple alleles to a gene and each have different positions with regard each other.
You can have 1 of the following combinations...
- DD
- Dd (and the mirror which is written the same way)
- dd
Each of these are made of 1 allele from a mother, and 1 from the father (obviously), each of them having 1 of the above sets...
So lets just go through a few generations assuming all possible combinations occur in their children...
G1a(DD) and G1b(dd) will have the following children:
Yup that's it, but we haven't started the inbreeding yet, so let's continue...
G1a(DD) - G2a(Dd) breed and can produce the following
G1b(dd) - G2a(Dd) can produce :
So what we see here is that a mating of G1a and G2a is perfectly fine, but assuming the recessive trait is bad, G1b and G2a has a 75% of a having a child with the recessive that is a problem, so let's go down that path... where we see the problem emerge...
G2a(Dd) - G3c(dd) will get you :
G2a(Dd) - G3c(Dd) will get you :
In other words, this set up just give you an infinite loop, which sucks, but this is really rather normal so there is no real issue here. The issue comes when...
G3c(dd) - G4b(dd) mate and produce the following off spring :
G5a(dd)
Notice how there is 100% chance of this occuring? The recessive becomes 100% likely, but so long as you don't get 2 parents with both alleles recesive then you won't have this problem.
This being the case solution is simple, just make sure noone with 2 recessive mate with another one... or do the reverse and make sure they do, if the trait is positive. This is how all our dog breeds came into being so you might not want to...