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Old 2010-02-15, 07:59   Link #1
milan kyuubi
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Negative effects of inbreeding within humans?

I was reading about this in Harry Potter. They said one family that was obsessed with keeping their blood pure, so they married cousins many times. The affect was that after generations of inbreeding they became violent and unstable. I'm wondering what happened to their DNA to cause this. I heard it was lack of 'fresh' genes, but I never got a proper explanation.

Also...
Scientists found that humans and chimps have a higher than expected number of genetic mutations due to inbreeding. Inbreeding isn’t necessarily limited to matings between people who are close relatives, it can also refer to matings between members of a small population where the genetic variation is small.

In modern life, inbreeding is still a concern in some populations. Public health experts in western Galilee have begun a project to educate citizens in areas with large Arab populations about the dangers of inbreeding.

I am also interested to find out how this affect people and their children. How does this genetic disorders develop, and is there some cure for this?
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Old 2010-02-15, 09:26   Link #2
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The different traits, alleles, found in genes have different levels of dominance. To decide a trait for the individual, you have to pair up 2 alleles from the parents.

If one allele is dominant, e.g. black hair, the other is recessive, e.g. red hair, the child will have black hair.

If both are the same allele, they will have simply have the trait which both alleles carry.

So in order to be a rare red head, you need parents who both have the recessive red hair allele in their genes.

Most genetic mutations and defects are recessive genes. If your family has a rare defective allele in the genes, you would not want to inbreed, you might bring out that rare defect.

In order to reduce the chance of bringing out such defects, variation of genes is important.

Variation of genes will likely bring dominant genes to the top and make recessive genes even more rare. This is why recessive yet appealing traits like red heads are becoming an endangered hair colour.
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Old 2010-02-15, 09:40   Link #3
milan kyuubi
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But what if a child prodeced by inbreeding have child with someone with fresh genes, would there children suffer the same consequences as the parent?
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Old 2010-02-15, 09:40   Link #4
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Quote:
Originally Posted by C.A. View Post
The different traits, alleles, found in genes have different levels of dominance. To decide a trait for the individual, you have to pair up 2 alleles from the parents.

If one allele is dominant, e.g. black hair, the other is recessive, e.g. red hair, the child will have black hair.

If both are the same allele, they will have simply have the trait which both alleles carry.

So in order to be a rare red head, you need parents who both have the recessive red hair allele in their genes.

Most genetic mutations and defects are recessive genes. If your family has a rare defective allele in the genes, you would not want to inbreed, you might bring out that rare defect.

In order to reduce the chance of bringing out such defects, variation of genes is important.

Variation of genes will likely bring dominant genes to the top and make recessive genes even more rare. This is why recessive yet appealing traits like red heads are becoming an endangered hair colour.
What he said, but I would like to add something :

A recessive or dominant gene is judged by the scientific community, but not exactly all said dominant genes are so called good. For example : good looking facial features are a mix of dominant genes and recessive genes, as the overall look is a combination of the shape of the nose, size of the cheeks, colour of eyes, cat-ears in females, etc. If we take all the termed dominant genes we would create a hideous looking genius.

Quote:
Originally Posted by milan kyuubi View Post
But what if a child prodeced by inbreeding have child with someone with fresh genes, would there children suffer the same consequences as the parent?
Eh, I need you to define fresh genes. Sorry.

In-breeding may be convenient (why go all the way out and spend lots of money on a female schoolmate, when you can just do your cousin if your culture doesn't forbid?), but it is the later generation that will suffer due to the genetic heritage, and higher reoccurence of defective or dysfunctional genes.

Think of the next generation. Your financial sacrifice will be remembered if your descendant is intelligent enough.
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Old 2010-02-15, 09:56   Link #5
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Quote:
Originally Posted by SaintessHeart View Post
Eh, I need you to define fresh genes. Sorry.
I meant if a man took a wife that he is not in family relationship . By doing that he will add a new set of genes to their offspring. Would their child inherit inbreeding genes like the parrent/father or not?
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Old 2010-02-15, 10:07   Link #6
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I meant if a man took a wife that he is not in family relationship . By doing that he will add a new set of genes to their offspring. Would their child inherit inbreeding genes like the parrent/father or not?
There really is no such thing as an "inbreeding gene", only genes that are commonly expressed within a genetic lineage who's expression is repeated and possibly amplified due to repetition of the same genes rather than diversity through the introduction of other genes.

The biggest issue with inbreeding is the amplification and expression of genetic traits, as this becomes a major issue because the commonalities between consanguineous people makes certain traits all the more amplified and expressed due to concentration of specific genetic material rather than genetic diversification.

And this is just Mendelian. I won't even touch the subject of multifactorial traits and non-Mendelian genetics. That's too comlicated even for my educational attainment. So basically what the others have said.

I was about to go get my genetics textbook but then I realized I might bore you people to death with SCIENCE!
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Old 2010-02-15, 10:11   Link #7
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Originally Posted by MeoTwister5 View Post
I was about to go get my genetics textbook but then I realized I might bore you people to death with SCIENCE!
I watched all episodes of endless eight. You can't bore me.
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Old 2010-02-15, 10:18   Link #8
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Inbreeding is not always bad, if the people involved only have "good" alleles. Of course, the vast majority of people are not genetically perfect supermen.
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Old 2010-02-15, 10:35   Link #9
milan kyuubi
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I have a friend which grandfather and grandmother from his fathers side were cousins. His grandfather being uncle to his grandmother. Will this have any effect on him?
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Old 2010-02-15, 10:36   Link #10
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Quote:
Originally Posted by justsomeguy View Post
Inbreeding is not always bad, if the people involved only have "good" alleles. Of course, the vast majority of people are not genetically perfect supermen.
Quote:
Originally Posted by MeoTwister5 View Post
I was about to go get my genetics textbook but then I realized I might bore you people to death with SCIENCE!
Meo, do me a favour. Explain to him the triggers of recessive genes using the concept of dormant and active genes influencing human physical traits at the point of fetal development. My old biology encyclopedia is currently buried somewhere in my room and I am too lazy to look for it.

Justsomeguy - The things he explain might be a little complex, but try to absorb it. Remember to give him a cookie if he does.

Quote:
Originally Posted by milan kyuubi View Post
I have a friend which grandfather and grandmother from his fathers side were cousins. His grandfather being uncle to his grandmother. Will this have any effect on him?
Not if he doesn't marry into anyone in the family. If I am not wrong, recessive genes only trigger at high saturation. It is just like if more people like Tsumugi Kotobuki go into an all girls school, there will be a higher occurence of lesbian cases in that particular school.

To further clear up any confusion : not all the genes in the pool are used in the zygote stage of development. Some of them remain untriggered, these are called dormant genes. The ones responsible for what you are today are called activated genes.

So when a sperm meets an egg, the mixture of genes that change the mutation rate and traits of the stem cells are supposedly to be something like a hypothesis testing sequence (Statistical Mathematics). However, it is still unknown if triggering any genes may cause a chain reaction into triggering a secondary gene.
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Old 2010-02-15, 11:29   Link #11
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Quote:
Originally Posted by milan kyuubi View Post
In modern life, inbreeding is still a concern in some populations.
Actually, there are no human societies that encourage inbreeding. Humans naturally avoid inbreeding by a mechanism we evolved - it's called incest aversion.

You don't develop much sexual desire for females you closely grew up with.

But on the other hand, if you've never met your blood sister or brother until you were 18... now that's a different story. This happened to a Russian sibling/couple who didn't know they were blood-related, and the authorities tried to persuade them to stop having kids because the kids they have were already having a 1 in 4 chance of being born with a genetic defect.

Quote:
I have a friend which grandfather and grandmother from his fathers side were cousins. His grandfather being uncle to his grandmother. Will this have any effect on him?
In some cultures cousins are supposed to marry each other. It only takes one pairing with someone who's not blood-related to eliminate most potential genetic problems, other than the possibility that the non-blood related person also carries the same recessive genes, which is pretty unlikely.
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Old 2010-02-15, 11:30   Link #12
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Meo, do me a favour. Explain to him the triggers of recessive genes using the concept of dormant and active genes influencing human physical traits at the point of fetal development. My old biology encyclopedia is currently buried somewhere in my room and I am too lazy to look for it.

Justsomeguy - The things he explain might be a little complex, but try to absorb it. Remember to give him a cookie if he does.
Right now I'm too lazy to explain it scientifically lol so I'll do it from memory.

If anyone wants to know, in the most basic sense dormant and active genes usually refer to the way a certain gene of one allele pair of one chromosomes sometimes tend to be "shut-off" in utero due to as of yet undiscovered means, which leads to a specific gene of a specific locus of the other active chromosome to be expressed regardless of dominance or recessiveness. In this sense, recessive and dominant genes do not necessarily convey an absolute effect of genotype and phenotype. This is also the cause of the phenomenon known as "genetic mosaicism" where certain cells of the body express one genetic trait while other cells express the other, which happens when the shut-offs happen later and fifferent cell lines shut-off different genes.

An example would be heterochromia, which in itself would be awesome and freaky.

There's also the issue regarding penetrance but I can't remember it right now.
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Old 2010-02-15, 11:43   Link #13
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Quote:
Originally Posted by MeoTwister5 View Post
Right now I'm too lazy to explain it scientifically lol so I'll do it from memory.

If anyone wants to know, in the most basic sense dormant and active genes usually refer to the way a certain gene of one allele pair of one chromosomes sometimes tend to be "shut-off" in utero due to as of yet undiscovered means, which leads to a specific gene of a specific locus of the other active chromosome to be expressed regardless of dominance or recessiveness. In this sense, recessive and dominant genes do not necessarily convey an absolute effect of genotype and phenotype. This is also the cause of the phenomenon known as "genetic mosaicism" where certain cells of the body express one genetic trait while other cells express the other, which happens when the shut-offs happen later and fifferent cell lines shut-off different genes.

An example would be heterochromia, which in itself would be awesome and freaky.

There's also the issue regarding penetrance but I can't remember it right now.
I think it would be more towards expressivity than penetrance. Like how much of an effect that triggered recessive gene would affect the person in total, e.g earlobes, in which the length would be how expressive the gene is.

Penetrance is used more on a population level than on family level. Unless, of course, the parents love children so much that they have 38, or the society is screwed up enough to encourage mass inbreeding.
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Old 2010-02-15, 11:51   Link #14
milan kyuubi
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Spoiler for Hominid inbreeding left humans vulnerable to disease:


The cliche has always been that in-breeding causes genetic diseases. A good example in history was the family prevalence of the genetic disease hemophilia in certain European royal families, who tended to marry other royals. Another example is the increased prevalence of genetic diseases such as Tay Sachs disease in certain Jewish populations, because they encouraged arranged marriages within the same ethnic population.
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Old 2010-02-15, 13:46   Link #15
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Quote:
Originally Posted by SaintessHeart View Post
A recessive or dominant gene is judged by the scientific community, but not exactly all said dominant genes are so called good. For example : good looking facial features are a mix of dominant genes and recessive genes, as the overall look is a combination of the shape of the nose, size of the cheeks, colour of eyes, cat-ears in females, etc. If we take all the termed dominant genes we would create a hideous looking genius.
A dominant gene suppresses the expression of a recessive gene and that's about it. They can both good or bad and most of the time they are neither. There is no single gene for "genius" or "hideousness" let alone have they been shown to be dominant and recessive respectively.

Furthermore, the whole dominant/recessive model is oversimplified, as this is a question of degree. And genes that are absolutely fatal when they come in pairs may well have a benefit when they are alone. After all, one should suspect there is a reason why they are still around.
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Old 2010-02-15, 13:52   Link #16
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Marrying first cousins is not automatically "bad" and in fact it was fairly normal in most societies for several thousand years simply because most human beings rarely traveled more than 10-20 miles from their birthplace once agriculture became the norm in human society. Often times, all your possible choices were related to you by first or second cousin.

The *only* reason it became taboo is that when the Industrial Revolution started and people started moving to large cities.... it became the fad that marrying a cousin was likely to get you defined as a "hick"/"countryboy" or otherwise un-citified.

The other posters have thoroughly explained the actual genetics so I won't repeat. The chances of having a child with a problem from marrying a first cousin are no more likely than trying to have a child at age 40 -- it increases the odds of a problem about 1%. Over half the states in the USA permit first cousin marriage. Most countries in the world have no legal restrictions on it.

So if you've grown up thinking cousin-marriage was a terrible thing -- you were the victim of a 100 year old urban myth.

Marrying a *non-blood-related* "sister" ... is, of course, no problem at all. Any mental resistance is a psychological effect from an evolutionary trait of "not being attracted to your nest-mates" - a variation on thinking of the 'girl next door' as more of a sister than a potential mate because you grew up together.
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Old 2010-02-15, 14:46   Link #17
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Originally Posted by Lio View Post
Actually, there are no human societies that encourage inbreeding. Humans naturally avoid inbreeding by a mechanism we evolved - it's called incest aversion.
Actually,... that's a cultural thing
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Old 2010-02-15, 15:14   Link #18
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There is an apparent evolutionary trait that's been discussed on the forums before that seems independent of culture (and is present in multiple species). Many species seem wired to "not be attracted" to nest-mates on average - even if they are not blood-related. The trigger is being raised closely together. Some species don't have it, some do.

I'm having trouble recalling the name of the phenomenon though -- perhaps someone with more focus could recall it
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Old 2010-02-15, 15:31   Link #19
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Can we change the title of this thread and name it "Negative effects of breeding with humans". That would be far more interesting....
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Old 2010-02-15, 15:41   Link #20
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Inbreeding makes blood related sicknesses more probable to pass down generations. Tissue mishaps are also more common within closed spawns. (A slang term for an inbred child.) It's because humans are made to blend with each other to gain the correct middle ground and balance the certain spots in each other's DNA, making each generation more "capable" and more balanced.

Of course, this is the opposite in reality. Humans are getting dumber, not smarter.
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