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Poloboy · 01-06-2007, 11:39 PM

For the original question, I consider any kind of sexual relations with close blood relatives gross - that's just personal opinion and I wouldn't presume to judge what other people find appealing or unappealing.

That's independent of the science, though. I certainly do think it's irresponsible of people to procreate with close relatives when they (a) are aware of the risks to the resultant child, (b) live in a community in which there is no justifiable social advantage to procreating with a relative, and (c) there is opportunity to be with a nonrelative.

Several people have mentioned the genetics, but nobody has explained it in detail, and a few people just made vague universal but completely unsupported statements, maybe because they were convenient for their argument? Anyway, for those who are interested, genetics is a very important consideration. I know this thread is about personal opinion regarding consanguineous relations, but I feel obliged to clear up the misinformation.

The most important issue is with "recessive" hereditary diseases - in which a person must have 2 bad copies of a gene in order to be affected (remember how everybody has 2 copies of every gene?). This is what willravel was referring to when he kept saying "homozygous." In case you just got intimidated by the word and didn't bother to look it up, homozygous means you have 2 identical copies of a gene, but of course willravel was referring to identical bad copies of a gene. There are TONS of bad diseases that are autosomal recessive like cystic fibrosis, PKU, hereditary hemophilia, sickle-cell anemia, Tay Sachs disease, Gauchier's disease.

This is the risk: One of your grandparents either has such a disease, or is a carrier. If they are just a carrier, there is a 1 in 16 chance that both you and your first cousin will be carriers (have a bad copy of the gene). If your grandparent has the disease, there is a 1 in 4 chance that both you and your cousin will be carriers. Those are really scary odds. But that's the absolute minimum. That refers to only 1 bad gene, related to 1 disease in the child. The odds of a bad mix get a little bit higher when you consider homologous recombination during gametogenesis (formation of sperm and ova), and much much higher when taking into account that there are ~25,000 genes, meaning there are more than 25,000 places to get a bad combination in the child.

Think this is all numbers and strange words? Here are some real-world examples:

The Bedouin of the Middle East and North Africa consist of many nomadic groups. Some of the groups in Israel have an incredibly high rate of deafness. Worldwide, early-onset deafness is estimated at about 1/2000 to 1/3000 births, and only about half of these are inherited. In Israeli Bedouin communities the prevalence is about 1/40, and has been confirmed to be due to a single mutation that is propagated by the extremely high rate of first- and second-cousin marriage. Even though deaf-deaf marriages are discouraged, the frequency of the mutant allele (copy of the gene) continues to increase from the inbreeding.

In many isolated Amish and Mennonite communities in North America, cystic fibrosis is dramatically over-represented compared to average North American caucasian numbers. The prevalence in North America is about 1 in 2500-3000 live births, with many different mutations potentially contributing to the disease. In the isolated communities, numbers as high as 1/500 have been found, with an otherwise rare mutation accounting for all cases in the community. There is no doubt that inbreeding within the small communities maintains the mutant allele at a high frequency.

On a final note, most people understand that genetic uniformity (a lack of variation) in a population makes it very vulnerable to epidemic disease. This caused the potato blight in Ireland, and led to the mass exodus of Irish that helped shape a lot of the large North American cities like Boston and Montreal. This is also a common argument against genetically modified crops (although its validity as a legitimate concern is still very contentious). The point is, people generally understand that genetic uniformity is bad, so it should be easy to understand that inbreeding, which contributes to genetic uniformity, can have very dangerous consequences.

01-06-2007, 11:39 PM	#131 (permalink)
Poloboy Insane Location: Canada	For the original question, I consider any kind of sexual relations with close blood relatives gross - that's just personal opinion and I wouldn't presume to judge what other people find appealing or unappealing. That's independent of the science, though. I certainly do think it's irresponsible of people to procreate with close relatives when they (a) are aware of the risks to the resultant child, (b) live in a community in which there is no justifiable social advantage to procreating with a relative, and (c) there is opportunity to be with a nonrelative. Several people have mentioned the genetics, but nobody has explained it in detail, and a few people just made vague universal but completely unsupported statements, maybe because they were convenient for their argument? Anyway, for those who are interested, genetics is a very important consideration. I know this thread is about personal opinion regarding consanguineous relations, but I feel obliged to clear up the misinformation. The most important issue is with "recessive" hereditary diseases - in which a person must have 2 bad copies of a gene in order to be affected (remember how everybody has 2 copies of every gene?). This is what willravel was referring to when he kept saying "homozygous." In case you just got intimidated by the word and didn't bother to look it up, homozygous means you have 2 identical copies of a gene, but of course willravel was referring to identical bad copies of a gene. There are TONS of bad diseases that are autosomal recessive like cystic fibrosis, PKU, hereditary hemophilia, sickle-cell anemia, Tay Sachs disease, Gauchier's disease. This is the risk: One of your grandparents either has such a disease, or is a carrier. If they are just a carrier, there is a 1 in 16 chance that both you and your first cousin will be carriers (have a bad copy of the gene). If your grandparent has the disease, there is a 1 in 4 chance that both you and your cousin will be carriers. Those are really scary odds. But that's the absolute minimum. That refers to only 1 bad gene, related to 1 disease in the child. The odds of a bad mix get a little bit higher when you consider homologous recombination during gametogenesis (formation of sperm and ova), and much much higher when taking into account that there are ~25,000 genes, meaning there are more than 25,000 places to get a bad combination in the child. Think this is all numbers and strange words? Here are some real-world examples: The Bedouin of the Middle East and North Africa consist of many nomadic groups. Some of the groups in Israel have an incredibly high rate of deafness. Worldwide, early-onset deafness is estimated at about 1/2000 to 1/3000 births, and only about half of these are inherited. In Israeli Bedouin communities the prevalence is about 1/40, and has been confirmed to be due to a single mutation that is propagated by the extremely high rate of first- and second-cousin marriage. Even though deaf-deaf marriages are discouraged, the frequency of the mutant allele (copy of the gene) continues to increase from the inbreeding. In many isolated Amish and Mennonite communities in North America, cystic fibrosis is dramatically over-represented compared to average North American caucasian numbers. The prevalence in North America is about 1 in 2500-3000 live births, with many different mutations potentially contributing to the disease. In the isolated communities, numbers as high as 1/500 have been found, with an otherwise rare mutation accounting for all cases in the community. There is no doubt that inbreeding within the small communities maintains the mutant allele at a high frequency. On a final note, most people understand that genetic uniformity (a lack of variation) in a population makes it very vulnerable to epidemic disease. This caused the potato blight in Ireland, and led to the mass exodus of Irish that helped shape a lot of the large North American cities like Boston and Montreal. This is also a common argument against genetically modified crops (although its validity as a legitimate concern is still very contentious). The point is, people generally understand that genetic uniformity is bad, so it should be easy to understand that inbreeding, which contributes to genetic uniformity, can have very dangerous consequences.