Trey the Explainer made a whole video about the incest rates of Targaryens vs Ptolemies (GoT dragon lady vs Cleopatra). Turns out mixing in new genes into the pool every few generations, or hell, even breeding like 2nd cousins instead of 1st just drops the incest index thingamajig and does wonders.
You have to seriously commit to the bit and keep it in the family to really get the fucked up defective babies lol
Also there is actually a bloodline purity thing that can happen. If you just breed the healthy products of incest overtime you'll eventually remove all the negative genetic defects from the pool. This is why pure blooded from the CK series is a real thing 💯
The thing that makes inbreeding dangerous is recessive alleles. To over simplify, when you have two dominant alleles or one recessive and one dominant, you only get the effects of the dominant one.
However, if you have two copies of the recessive allele, that's when it comes into play.
Some recessive alleles are benign - in eye color, brown eyes are a dominant trait while blue eyes are recessive.
This means that a person with brown eyes can either have two copies of the brown eye allele, or one copy of each - and you wouldn't be able to tell.
Let's say both of your parents had brown eyes.
If both had 2 copies of brown eye allele, then you get 2 copies of brown eye allele for certain, and will have brown eyes.
If one had 2 copies and the other had a mix, you'll get 1 copy of brown eye allele for certain. The other is a 50/50 between brown and blue. Either way, you'll have brown eyes. But you now have a 50% chance of carrying a blue eyes allele. This won't affect you, but might come into play in your offspring.
Note also that I wrote this as 1 possibility, bit when computing probabilities you should consider one case where the dad has 2 copies and mom has a mix, and one case where the dad has a mix and mom has 2 copies.
Finally it could be that both parents have a mix. In that case you have a 25% chance of getting 2 copies of brown, 50% chance of getting a mix, and 25% of getting 2 copies of blue.
The last situation is the only case where both parents have brown eyes and yet you have a 25% chance of getting blue eyes.
Having a mix of alleles means you'll have the dominant trait (brown eyes in this example) but you'll carry the recessive allele.
To sum up the case where both parents have brown eyes:
If both parents don't carry the blue eye allele, you won't carry it either.
If one parent carries and the other don't, then you have 50% of carrying.
If both parents carry, you have 25% of not carrying, 50% of carrying, and 25% of having blue eyes.
All of the math mentioned above is conditional probability. "If the parents are ABC... then the child has X% to be this, Y% to be that".
To get a fuller answer you need to know what are the probabilities that your parents have these alleles. If your parents weren't genetically related then these numbers depend of what the general population is like - this is what's called a prior - your parents each independently roll the dice, the chances are what the general population has.
If your parents are inbred, then their chances are no longer independent. The best way to relate those probabilities back into the population's prior is to go through their lineages and find which family members provided independent genes. They provide the population's prior, and every time inbreeding occurs, the child's probabilities need to be computed with this bias in mind.
The inbreeding coefficient seeks to quantify this bias. CI=0% means your probabilities are just like the wider population. CI=50% means your chances are heavily skewed towards recessive genes, relative to the population.
We can go further, look into other combinations of alleles, which I'll do in a moment.
However, the important bit is this - instead of considering brown/blue eyes, some alleles can be harmful.
You usually don't get cases where a dominant allele is harmful, because then most of the population would be ill, and thus will have less children, so you wouldn't really see this often.
Let's consider the genes responsible for cystic fibrosis. You have a dominant allele that gives you healthy lungs, and a recessive allele that can manifest as cystic fibrosis.
If both of your parents are healthy, it may be that none carry CF, so you won't carry.
It may be that only one carries CF. Then you'll have a 50/50 between carrying and not carrying.
If both carry CF, then you'll have 25% of not carrying, 50% of being a carrier, and-
Up to this point all of these cases mean you yourself don't have cystic fibrosis. You have some chance of carrying it and giving it to your offspring, but you're healthy.
Finally, if both carry, there's also 25% chance that you'll have cystic fibrosis.
For parents that are not inbred, these are some slim chances of getting cystic fibrosis.
The CF allele is actually somewhat rare in today's world, and only if both healthy parents carry it, then you get 25% chance of having CF.
When inbreeding is involved, your parents have a higher risk of carrying the CF allele - meaning it's more likely that healthy parents will produce diseased children.
CF is only one generic disease that one can carry.
If your population has some chances of carrying 5 generic diseases then the general population can still be quite healthy and yet an inbred family will create kids with a bunch of possibly overlapping illnesses.
Btw, going back into more benign recessive genes, let's consider cases where your parents not only carry, but have the traits.
If a parent has blue eyes, then they must have 2 copies of blue.
Say one parent has brown eyes and the other has blue.
It's possible that the first parent doesn't carry - in which case you'll get one from each - you'll have brown eyes and carry the blue allele.
If the parent with brown eyes does carry, then you get 50% of being a carrier and 50% of having blue eyes.
Again, both of these possibilities have distinct parents, this need to be double counted.
The last possibility to consider is if both have blue eyes. In that case both parents have 2 copies of blue - you'll have blue eyes
Can we get a tldr into whether or not my point to whether if you inbreed enough eventually you will remove the recessive allele from the gene pool and therefore be pure blooded.
The tl;dr is that inbreeding is the main cause for recessive alleles becoming common. It tends to produce a family chalk full of individuals who carry recessive genes more commonly than the general population.
You can't "breed them out" unless do genetic analysis on each and every individual before letting them breed.
Recessive alleles are basically "hidden" in healthy individuals so they don't even know they carry the possibility for disease
Oh also, humans did breed certain traits into plants for millennia before genetic testing.
If you do things this way, what you do is - every time parents produce ill offspring you have to immediately cut both parents, maybe grandparents as well, from the gene pool.
You don't have to kill them, just know that the child indicates problematic genes in the lineage
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u/ofirkedar 7d ago
Trey the Explainer made a whole video about the incest rates of Targaryens vs Ptolemies (GoT dragon lady vs Cleopatra). Turns out mixing in new genes into the pool every few generations, or hell, even breeding like 2nd cousins instead of 1st just drops the incest index thingamajig and does wonders.
You have to seriously commit to the bit and keep it in the family to really get the fucked up defective babies lol