Taboos

[theDespiser]

Your Moralising Quotient is: 0.67.

Your Interference Factor is: 0.40.

Your Universalising Factor is: 0.80.

kinda surprising, considering what i know about myself

[Avatar]

Which is?

Surprising in which direction?

Thoughts man, give us your thoughts!

--Avatar

[High Lord Tolkien]

Your Moralising Quotient is: 0.87.

Your Interference Factor is: 0.60.

Your Universalising Factor is: 1.00.



I'm a straight shooter, baby!
Which, knowing myself as I do is pretty damn funny.

Although I do really draw the line when it comes to poultry lovin'.

[Prebe]

I don't agree on the neutrality of inbreeding Kins. Creating a genetically uniform population (which inbreeding will do) will make for a lower degree of adaptability and a higher degree of vulnerability (on population level) to pathogens.

[sgt.null]

as in the British royalty and hemophelia?

[Prebe]

Those are the recessive genetic traits Kins is talking about. He is saying that without those, inbreeding would be neutral.

Even with that distinction I disagree as you can see.

[Avatar]

I think that we're thinking of two different things here. Creating a genetically uniform population would be the result of massive and wide-ranging inbreeding.

If the recessives weren't a problem, there is the potential for that, but I doubt everybody would suddenly start breeding with their relatives. so inbreeding on a limited scale, and it would, I think, be extremely limited, would be neutral on an individual level.

Hell, even with recessives, wouldn't it take a couple of generations for them to start affecting things?

--A

[Prebe]

Creating a genetically uniform population would be the result of massive and wide-ranging inbreeding.

Which could easily take place in isolated populations. The smaller the population the larger the likelihood that potentialy advantageous genes disapear by genetic drift. This would leave any individual of that population more vulnerable to changes in the environment (which is really the key issue here).

A static environment favours inbreeding, though a lot of individuals will snuff it in the process.

The extreme result of inbreeding is equivalent to asexual reproduction. We just have to look at the success of sexual reproduction to conclude that inbreeding is probably generally a bad thing.

[Avatar]

Certainly, in the genetic sense of maintaining diversity to better protect a population from the potential of changes which cannot be adapted to.

Genetically, inbred populations are effectively self-limited. Inbreed too much, and eventually your population will be wiped out.

That however, doesn't signify in terms of the cultural taboo that we were discussing. Elimination of the recessives, (the biological rationale behind the taboo) would eliminate the need for it.

Agreed, that genetically it is not advantageous to the species. In the cultural sense though, one man sleeping with his sister isn't going to have a noticable effect on the populations gene pool.

--A

[Prebe]

Genetically, inbred populations are effectively self-limited. Inbreed too much, and eventually your population will be wiped out.

No. That is simply not true. As I said, a very static environment favours genetic similarity, making inbreeding an advantage.

As for the cultural aspect, I'll go back and read the thread, sorry

Edit: I recall hearing "Da Witness of Jah" saying that the reason that inbreeding was not a problem between Adam and Eve, was that their genes were perfect (no deleterious recessives here). And well, I guess that Eden would have been a pretty static place. Come to think of it, where would we all have been, if they hadn't been kicked out?

[Avatar]

No need to apologise.

Genetically, inbred populations are effectively self-limited. Inbreed too much, and eventually your population will be wiped out.

No. That is simply not true. As I said, a very static environment favours genetic similarity, making inbreeding an advantage.

Perhaps I was unclear...I meant given the fact that recessives exist and are reinforced by inbreeding. Eventually, your breeding population would become so genetically defective that it would become unviable, wouldn't it?

--A

[Prebe]

Nope, the deleterious recessives would actually be effectively rooted out. Immagine (for simplicity) a population starting with two individuals each carrying one lethal recessive allele. Start the experimental breeding from there and see what happens to the allele.

[Avatar]

Aha, I think I'm with you. The bad allele's would reinforce each other, causing a fatal birth defect, eliminating that gene from the pool. That makes sense.

But then, isn't that an example of the self-limiting nature of inbreeding? Nature itself prevents the spread of the lethal gene?

Would the same hold true for non-fatal recessives? What about a gene for poor vision? In a closed system? Eventually everybody would be blind?

--A

[Prebe]

Aha, I think I'm with you. The bad allele's would reinforce each other, causing a fatal birth defect, eliminating that gene from the pool. That makes sense.

Almost. The homozygotes would not live, and the heterozygotes would have fewer viable children (because one in four children of heterozygotes would not live). In fact, the more heterozygotes in the population, the fewer viable children other heterozygotes would have (this is the actual inbreeding effect). This would eventually lead to the disappearance of the allele.

But then, isn't that an example of the self-limiting nature of inbreeding? Nature itself prevents the spread of the lethal gene?

. Actually a recessive deleterious allele would have a better chance of "staying alive" in a large heterogenous population (remember that the likelihood of two heterozygotes mating would be smaller in such an environment).

Would the same hold true for non-fatal recessives? What about a gene for poor vision? In a closed system? Eventually everybody would be blind?
--A

No, not if vision was an advantage in the population. The effect of inbreeding on the "bad" recessive allele would be the same, though less pronounced if the effect of homozygosity is not lethal.

edit: If the lingo gets you down let me know. But I don't think it will "Mr. Rennaisance Man"

[Avatar]

This is why I like having you around Prebe.

Ok, I think I'm following. I didn't take it past the first reinforcement, and consider the couple as the base of a breeding population.

In fact, the more heterozygotes in the population, the fewer viable children other heterozygotes would have (this is the actual inbreeding effect).

Because of the greater chance of two recessives combining?

Let me see, out of 4 children from parents with 1 recessive each, 1 would die, two would carry recessives, and the 4th would be "clean"?

The larger the population, the less chance that the lethal recessives would meet, meaning that it could be passed as an inactive recessive to more people?

OK, I can see how in a small, closed population, a gene which was lethal would eventually be weeded out, by simple virtue of the fact that dominant bad alleles would mean a reduction in the number of offspring with a recessive, and an increase in the number of offspring from "clean" pairings. (Right? ) (The notepad next to my keyboard is now covered in little columns and rows of Ab's connected by lines. )

Now let's go back to the blindness...what if it's not a disadvantage? Say that the sighted population cares for the blind, and blind people (afterall, we're talking about people) can live normal lives, have children, etc. It's not an advantage, but it's not a disadvantage. (Human interference).

Because it's not fatal, the gene wouldn't be weeded out. In other words, children carrying it would still be born, have children who also arried it, etc. Wouldn't that increase the chance of a negative reinforcement? Make it more likely that two recessives would combine?

And then to the real crux of this...if inbreeding automatically eliminates bad alleles, what's wrong with incest, genetically speaking? The promotion of increased genetic homogenity?

If the population is an open one, I could see how new genes wouldn't get a chance to become established if the homogenity was already entrenched, but if it's a heterogenous genetic pool, then a little inbreeding wouldn't make much of a difference, would it?

(And everybody else bear in mind I'm talking only the biological consequences here, not the psychological ones.)

--Avatar

[Prebe]

Because of the greater chance of two recessives combining?

Let me see, out of 4 children from parents with 1 recessive each, 1 would die, two would carry recessives, and the 4th would be "clean"?

Exactly.

The larger the population, the less chance that the lethal recessives would meet, meaning that it could be passed as an inactive recessive to more people?

Spot on.

OK, I can see how in a small, closed population, a gene which was lethal would eventually be weeded out, by simple virtue of the fact that dominant (now why did you have to say “dominant” here? You were doing so well . I think you mean prevalent) bad alleles would mean a reduction in the number of offspring (from anyone heterozygous for the gene), and an increase in the number of offspring from "clean" pairings.

Yes! (bold corrections mine)

(The notepad next to my keyboard is now covered in little columns and rows of Ab's connected by lines. )

You really made the experiment didn’t you?

Now let's go back to the blindness...what if it's not a disadvantage? Say that the sighted population cares for the blind, and blind people (afterall, we're talking about people) can live normal lives, have children, etc. It's not an advantage, but it's not a disadvantage. (Human interference).

That is something quite different. This example is very well in line with the hemophelia in the british royals. In nature this would be a lethal recessive for all practical purposes. But if you are loosing all selective pressure, only chance rules what genes prevail. All may go blind, or all may not.

To give a more general answer that you can work with, here are a few rules:

Allele frequencies in populations remain constant (adhering to the Hardy Weinberg proportions) if:

1: There is no selective pressure
2: No immigration/emigration
3: No mutations
4: Random mating
5: No genetic drift (usually assumed if population size is practically infinite)

In a small population one can’t assume 5. The smaller the population, the higher the probability, that any allele will disappear from the population due to genetic drift. If you select family members for mating, of course you can’t assume 4 either.

In my simple example it is clearly the selective pressure that roots out the allele.

To make a long story short: neutral alleles will (in very small populations) either disappear or take over, due to genetic drift. On top of that, any deviation of the five rules above, will generally lead to changes in allele frequencies. These changes are called, hang on to your hats, EVOLUTION.

[Avatar]

OK, I can see how in a small, closed population, a gene which was lethal would eventually be weeded out, by simple virtue of the fact that dominant (now why did you have to say “dominant” here? You were doing so well . I think you mean prevalent) bad alleles would mean a reduction in the number of offspring (from anyone heterozygous for the gene), and an increase in the number of offspring from "clean" pairings.

Yes! (bold corrections mine)

No, I meant "dominant" but I think I see the distinction now that I think about it. Prevelance in population rather than dominance in an individual (which would mean a dead individual anyway.)

(The notepad next to my keyboard is now covered in little columns and rows of Ab's connected by lines. )

You really made the experiment didn’t you?

Had to...can't visualise these things. AA=clean, bb=dead.

Thanks for the clarification. I wasn't thinking of the elimination in terms of selective pressure exerting an influence on it. I was thinking more along the lines of no pressure, leading to rampant proliferation of the non-fatal defect throughout the population over time. From what you say though, it seems that this is not a given, only a possibility?

I wonder how much selective pressure exists in terms of human populations today? I suppose it differs according to circumstances and populations though, with some circumstances/environments exerting significant pressure, and others very little.

So now, considering we're talking about inbreeding, while we have no selective pressure, and no immigration, we also have genetic drift (small population) and no random mating. Ergo allele frequencies do not remain constant, therefore greater chance of any given allele being eliminated?

...but if it's a heterogenous (large, open-ended?)genetic pool, then a little inbreeding wouldn't make much of a difference, would it?

(Thanks for the explanation. )

--A

[Prebe]

I was thinking more along the lines of no pressure, leading to rampant proliferation of the non-fatal defect throughout the population over time. From what you say though, it seems that this is not a given, only a possibility?

Only a possibility, yes. alleles only "rampantly proliferate" if they confer a selective advantage, or if they are tightly linked to alleles that do (close proximity on the chromosome).

No, I meant "dominant" but I think I see the distinction now that I think about it. Prevelance in population rather than dominance in an individual (which would mean a dead individual anyway.)

Exactly.

Ergo allele frequencies do not remain constant, therefore greater chance of any given allele being eliminated?

Or becomming the only one, if no selective pressure exists. The initial allele frequency has a large impact on whether an allele becomes prevalent or is eliminated. The smaller the population, the larger the impact. A consequent selection of related sexual partners would have the same effect as lowering the population size: The likelihood of having two alleles identical by descent would increase. As would the likelihood that Hardy- Weinberg proportions are displaced at a given locus.

Hardy-Weinberg proportions tell something about the distribution of heterozygotes and homozygotes of a given locus. If two different alleles P and Q exist in a population at a given locus with the allele frequencies p and q. N is the number of individual in the population. the EXPECTED distribution of genotypes is:

Genotype QQ (homozygote) is N*q^2
Genotype PP (homozygote) is N*p^2
Genotype PQ or QP (Heterozygotes) is N*2*p*q

[Avatar]

Ergo allele frequencies do not remain constant, therefore greater chance of any given allele being eliminated?

Or becomming the only one, if no selective pressure exists.

Aaha.

The initial allele frequency has a large impact on whether an allele becomes prevalent or is eliminated. The smaller the population, the larger the impact. A consequent selection of related sexual partners would have the same effect as lowering the population size: The likelihood of having two alleles identical by descent would increase.

OK, I'm with you. That would remain true for as long as offspring continued to be produced by related sexual partners in each generation. In an isolated (short-temr) incident, i.e. related partners producing an offspring, who then went on to breed with a random partner, the risk of any genetic "damage" would be minimal though, wouldn't it? One generation isn't enough to eliminate or increase the incidence of any given allele in a population, is it?

--A

[Prebe]

One generation isn't enough to eliminate or increase the incidence of any given allele in a population, is it?

No, not in a population of any considerable size.

I think we can now say that you have successfully passed evolutionary genetics 101 .

Your diploma is in the mail