Identical Twins and Homosexuality

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Orleander

OH JOY!!!!
Valued Senior Member
Since you are born gay, if you are gay does that mean your identical twin would be gay as well?
 
Orleander said:
Since you are born gay, if you are gay does that mean your identical twin would be gay as well?
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If one twin is gay, the other has about a 50% chance of being gay - so it's far from certain, but the odds are a lot higher than average. This seems to indicate that there's a substantial genetic component, but that genes aren't a single deciding factor.
 
I was surprised how rare the penetrance was in the other identical sib. So on guess homosexuality is 50-70% environmental or residual variance. Strange. Then again, they're coding what could be expressed quantitatively as a binary, so maybe odd ratios aren't so unexpected.
 
Just because it happens during pregnancy, doesn't mean it's not genetic. Genes as well as environment dictate how an organism develops. There are genes that are only active during embryonic phases, for example.
 
Orleander said:
Since you are born gay, if you are gay does that mean your identical twin would be gay as well?
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There is likely to be a genetic component to homosexuality. Scientific studies of homosexuality running in families agree with this. However, this does not mean that the trait is determined solely by genes. Like nearly every trait, there is almost certainly a mixture of nature and nurture (genes and environment) at play.

So, when it comes to monozygotic twins, homosexuality is like other complex personality traits – they may or may not be shared with the chances being almost impossible to determine beforehand.


Nasor said:
If one twin is gay, the other has about a 50% chance of being gay....
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Really? Who says this?
 
Hercules Rockefeller said:
Really? Who says this?
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Later that same year, Boston University psychiatrist Richard Pillard and Northwestern University psychologist J. Michael Bailey announced the results of their study of male twins. They found that, in identical twins, if one twin was gay, the other had about a 50 percent chance of also being gay. For fraternal twins, the rate was about 20 percent. Because identical twins share their entire genetic makeup while fraternal twins share about half, genes were believed to explain the difference. Most reputable studies find the rate of homosexuality in the general population to be 2 to 4 percent, rather than the popular "1 in 10" estimate.
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http://www.bri.ucla.edu/bri_weekly/news_050812.asp

Fraternal birth order's influence on homosexuality wasn't known at that time as far as I'm aware, so that may have altered the interpretation of these findings.
 
Orleander said:
could it be because of something happening during the pregnancy and it not being genetic?
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Hormonal changes in womb environment have been postulated as a factor. Perhaps a comparison between identical and fraternal twins may be useful.

One cannot underestimate the psychological effects of twins on each other. People expect identical twins to be similar.
 
orleander, there is a 50% chance that if you are schizophrenic then your identical twin will be too which means there is a genetic componant there as well (i cant rember the full list of percentages but it was an interesting list) however it shows its not CERTAIN that you will be and that there are enviromental factors as well (hense its not 100%)
 
So 1 in 3 are born gay so that means if you have triplets one of them are gay?
 
well, if its genetic, is it possible for one identical twin to have Down Syndrome and the other not?
 
No, I don't think so. The genetic abnormality that causes Downs Syndrome is a trisomy of chromosome 21 -- three copies of the chromosome in each cell, instead of two. So in order for this to happen, it would have had to obtain the extra copy from one of the parent gametes. Fusion of the gametes to form the zygote happens prior to the zygote spliting into two during the first cell division, which is when identical twin formation occurs.

I think.
 
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