Comments on: Swedish twin study: Q & A with J. Michael Bailey

By: Zoe Brain

Zoe Brain — Fri, 25 Jul 2008 02:00:52 +0000

My thoughts on the subject I invite critique - by Warren, by Bailey, by anyone with some knowledge of the subject.

By: Evan

Evan — Fri, 11 Jul 2008 05:45:00 +0000

Drowssap,
A brainscan costs around five thousand dollars each, I think. But the problem is:
Scanning the brains of discordant twins at adult age would not say much about what caused any different patterns that might be found. You would have to do a longitudinal study, scanning the brains of a group of twin pairs from their earliest years to adulthood to observe any significant changes in volumes, connectivity or activation. That is, if you can find some predictor of future orientation which is already present at the earliest age when brainscans can be performed. Such enterprise would be quite expensive and time-consuming. The risks are also big: you can fail to predict orientations and get useless data, some of them might quit halfway through the process, or if orientation is established before brainscans are performed you would only witness effects and the causes would remain out of sight.
I think a better approach would be to have a good and reliable collection of candidate genes and try to see how their expression would contribute to any observed brain patterns (and which could be attributed to other environmental causes). The Savic study is the second one, after last year’s Safron et al, which points to something in the amygdala region. They should zero in on that region and see if anxiety is a byproduct of orientation or a component. I think it’s a secondary component which fits Daryl Bem’s description of childhood ‘feelings of apprehension’ in the presence of same-sex peers. (What about the children who were not gender-nonconforming?…) The amygdala seems to take the punch of emotional interpretation, but in order for one gender to be perceived as unfamiliar, as Bem described it, there must also be something underexpressed in the one who perceives and does not fully identify with the perceived gender. Now that’s the hardest part to imagine what it could be. I’ve been talking on this blog about a handful of possible elements, from aggressiveness to anything that can work with(in) perception, like proprioception and brain maps of gender. I have no idea how they can look for aggressiveness expression in the brain which would have a bearing on gender perception (not on something else). It would be ideal if you could turn on or off some very specific brain areas and see which one makes the greatest difference then zero in on that area.

By: Drowssap

Drowssap — Fri, 11 Jul 2008 02:20:50 +0000

The logic of the common twin study (as opposed to the rare study of identical twins reared apart) depends on their being two types of twins that vary in their genetic similarity. The assumption is that this is the only salient way that such twins differ–other differences are presumed not to have an affect on the trait of interest.

Somebody needs to do another brain wiring study like “PET and MRI show differences in cerebral asymmetry and functional connectivity between homo- and heterosexual subjects.” This time do it on identical twins.
Take 10 pairs of identical twins, 1 straight the other gay.
Check to see if the same areas of brain wiring are more feminine in the gay twin than the straight twin.
Since…

The results cannot be primarily ascribed to learned effects, and they suggest a linkage to neurobiological entities.

… we’d have a pretty definitive answer.
Oh how I wish I had a million bucks to donate. Does anybody know how much research like this costs?

By: Evan

Evan — Thu, 10 Jul 2008 21:52:01 +0000

I don't know much about cloning types, Drowssap. I suppose they copy DNA material and they get a full duplicate of whatever they want to clone. But how monozygocity is caused no one knows right now. Neither do they know how identical identical twins really are. Apparently they're not fully identical and that can cause different phenotypes, including different types of diseases (like the one mentioned in the interview). Many things can happen along the way from DNA duplication to expression. It doesn't necessarily mean that events in the womb are the main influencing factors. Here's one study that focuses on the epigenetic differences that appear in the life of identical twins during their lifetime. One relevant quote:

By using whole-genome and locus-specific approaches, we found that approximately one-third of MZ twins harbored epigenetic differences in DNA methylation and histone modification. These differential markers between twins are distributed throughout their genomes, affecting repeat DNA sequences and single-copy genes, and have an important impact on gene expression. We also established that these epigenetic markers were more distinct in MZ twins who were older, had different lifestyles, and had spent less of their lives together, underlining the significant role of environmental factors in translating a common genotype into a different phenotype. Our findings also support the role of epigenetic differences in the discordant frequency/onset of diseases in MZ twins.

By: Drowssap

Drowssap — Thu, 10 Jul 2008 17:42:44 +0000

Evan

The differences between identical twins increase as they age, because environmentally triggered changes accumulate. But twins can also begin their lives with differences, according to Bruder’s study, and that calls into question their very name.
“Maybe we shouldn’t call them identical twins,” Harvard’s Bieber says. “We should call them ‘one-egg twins.'”

I knew that gene expression changes which genes are active throughout our lives. When genes become useful they have the propensity to kick on. On the flip side if they prove detrimental genes have the ability to turn off.
However I didn’t know that identical twins could start out different to begin with.
On a related note:
Clones would start out with precisely the same genes active because a clone is built from a fully expressed, adult strand of DNA. Is that correct or am I missing something on clones?