Question about Inbreeding

[Guardsman Bass]

This actually stems from my reading of Song of Fire and Ice, but it is a genetics question, so I posted it here.

It is mentioned that House Targaryen had been breeding brother to sister for almost 300 years. My question is, what would be the effects on the children born after such long-term inbreeding? Would it reach a point where the children would be so inbred and sickly that they would almost certainly die not too long after birth?

[Akhlut]

There'd definitely be inbreeding depression. How much, I'm not certain. Depends on how many generations there have been of brother-sister "relations" like this.

[Guardsman Bass]

The wikipedia chart is pretty messy, but it looks like 6 or 7 generations of almost solid brother-to-sister inbreeding, possibly more.

[Stormin]

Depends on how many nasty recessive genes and conditions there are before the inbreeding starts.

[Guardsman Bass]

I think I just found my answer, and an interesting paper on inbreeding, here. Apparently, after about 8-12 generations of inbreeding full brother and sister (which almost happened with the fictional Targaryens, and possibly did if you include their years in Valyria, where the custom emerged) in rodents, breeding success became almost non-existant, although there were a few exceptions born. This would probably happen to the Targaryens, if they kept it up.

[Sriad]

There's enough ambiant magic hanging around F&E world to suggest it had a little buoyant influence, but after the 6-10th-ish generations House Targaryen is showing more than its share of batshit insane and sickly members. (see siblings of Aegon the Unlikely [ie Aerion the self-immolating], Aeres II [The {more recently} Mad] and Viserys)

[Ace Pace]

The wikipedia chart is pretty messy, but it looks like 6 or 7 generations of almost solid brother-to-sister inbreeding, possibly more.

Pretty nice broken link.
This works

We definetly see a rise in the stupidty and madness average as the time goes on, but overall we see far more normals then I'd expect.

[Broomstick]

It also depends somewhat on whether or not "defectives" are ruthlessly eliminated at birth.

The pre-US Hawaiian royals practiced quite a bit of inbreeding, but they also killed at birth children that were identified as less than acceptable. That sort of ruthlessness will help keep the problem genes from piling up. Not indefinitely (and I believe Hawaiians didn't exclusively practice brother/sister marriages) but it will put off deterioration in the lineage.

[Guardsman Bass]

It also depends somewhat on whether or not "defectives" are ruthlessly eliminated at birth.

The pre-US Hawaiian royals practiced quite a bit of inbreeding, but they also killed at birth children that were identified as less than acceptable. That sort of ruthlessness will help keep the problem genes from piling up. Not indefinitely (and I believe Hawaiians didn't exclusively practice brother/sister marriages) but it will put off deterioration in the lineage.

It's possible, but there's no mention of it in the books. They may not have enough children per generation to pull it off. Plus, I remember it being mentioned as sort of a joke that when a Targaryen is born, the gods flip a coin, and the child ends up either crazy or great.

[Shroom Man 777]

How many generations of incest would it take to come up with gangly gollums or tall, big ogre retarded folk? How bad can prolonged inbreeding be?

I mean, I was inspired by this thread to make this.

[Junghalli]

How many generations of incest would it take to come up with gangly gollums or tall, big ogre retarded folk? How bad can prolonged inbreeding be?

I think that's mostly a myth there.
Inbreeding doesn't cause inherited disease, it simply makes children more likely to be heterozygotes. And a lot of inherited diseases are mutations on a recessive gene and therefore are only expressed in heterozygotes who have both pairs of the recessive mutated gene (crippling mutations on a dominant gene have a tendency to weed themselves out of the gene pool quickly, so they're less common). That's why you get higher incidences of inhereted disease with inbreeding, but the mutation has to be in the lineage already. Inbreeding doesn't cause diseases and deformities to somehow magically appear and pile up (as some X Files episodes and B movies would have you believe).
We could do a small demonstration here, say "f" is a deletrious mutation. To have the disease you have to be f-f
NORMAL REPRODUCTION
Parents:F-f ----- A-D
Children: F-A-----F-D-----f-A----f-D
INBREEDING
Parents: F-f ----- F-f
Children: F-F----F-f-----f-F------ff
At least this is AFAIK.

[AMX]

Homozygotes, not heterozygotes.
Heterozygotes have two different versions of the gene in question (so they don't show symptoms of recessive alleles).

Note also that many mutations can be beneficial for heterozygotes, but deleterious for homozygotes.

[The Yosemite Bear]

jokes about the Julians and the Poltemetics should be entering soon....

[Junghalli]

Homozygotes, not heterozygotes.

God I hate it when I screw up things that are intuitively obvious (homo=same).

[The Duchess of Zeon]

The Ptolemies practiced incest for 250 years through just as many generations, usually brother-sister, and still managed to produce Cleopatra, though the men of the family were entirely, hopelessly fucked up by that point. Cleopatra rather sensibly went for very genetically distinct Roman men, intentionally or not, so that her descendants (some did survive) were still around several centuries later.

[Lusankya]

It would make sense for the men to go downhill first. They have less redundancy to begin with.