A question about identical twins

You are an “innie” or an “outie” depending on whether the person who tied the umbilical cord was right- or- left-handed.

If we’re remembering the same case (which we may be, since the one I recall was posted here), it wasn’t a fingerprint, it was DNA evidence. From a drop of saliva, I believe.

WHAT?!!

… is this true?

Perhaps I should start a new thread for this as it may cause considerable argument however in regards to the people who bring up sexual orientation between Identical twins as some sort of proof they don’t have identical DNA; While there is some evidence that SOME homosexuals have differences in brain structure that seem to mirror differences in the opposite sex, there is no proof at all to the common assertion that you are ‘born gay’ or ‘born straight’. I have no doubt that genetics plays a significant, perhaps even majority role in sexual orientation however there is not a ‘gay gene’. Sexual orientation is not a light switch labeled straight or gay. The obvious fact that it is the GLBT (Gay, Lesbian, Bisexual, Transgendered (emphasis mine)) community means there are degrees of sexual orientation, it is a spectrum, not a bi-polar state. I would speculate that there are multiple genes that cause a varying tendency towards one sexual orientation or the other. I would also speculate that developmental factors, both physical, societal and environmental play a part as well, though nothing so hackneyed as the old Freudian “An overbearing mother + absent father = homosexual male”. I’m not gay myself, however I’ve known that there is nothing wrong with it since my late teens (as with many people in my youth I was both a poor reasoner and at my most vulnerable to social pressure). Every time I hear someone gay say “I was born that way” it bothers me, because it’s a response that seems to implicitly acknowledge that someone has a right to question your sexual orientation in the first place. If I was homosexual, I would say “I don’t have to have a reason or explanation for being gay, it’s just who I am” in those situations. Obviously this is IMHO however now that the human genome has been sequenced, the answer to the ‘gay gene/s’ is coming soon. What are they going to say about people who don’t have the genes, but still live a gay lifestyle? Are you going to have to pass a genetic test that proves you were actually ‘born that way’ to be accepted in gay society?

Way too much editorial from,
AllFree

[Moderating]

Going from navels to sexual orientation is a bit of a jump. I would suggest opening a new thread in GD for the latter subject rather than hijacking this one.

Colibri
General Questions Moderator

Like most complex phenotypes, the best we can say about sexual orientation is that it’s likely to have components of both multiple genetic influence and also significant environmental influence. It’s almost certainly going to be far far more complex than “I done got the gay gene!”

It’s a song by Paul SImon on the Graceland album
There’s no doubt about it,
it’s the myth of fingerprints,
I have seen them all and they are all the same.

IIRC from an article many moons ago…

Fingerprints are matched on the basis of points; where a ridgeline merges or comes to a dead end. Even in something like CSI, you will see the “automatic matching program” highlight points on the two images and connect them to indicate “these points match”. A 16-point match, IIRC(?), was considered by scientific studies (yes there are some) to be like DNA, a billion to one positive. The matching programs even use points. You can’t just overlay one on the other, as the photos need to be properly oriented; depending on the surface they may be distorted - stretched or compressed with a bit of skidding between halves of the print, etc.

The errors in the linked article most likely hinge on several things. First, the “expert” must determine where ridges end or merge; in a ragged smudged print that may be difficult. A news article about the Portland attorney mentioned that the print sample sent to the FBI was incomplete and a cruddy fax copy. Therefore, the points to match are somewhat subjective and open to interpretation. The article makes no mention of the quality or type of prints in the blind tests, other than to say “partial”.

So the computer matching may be positive, the subjective evaluaton of partial prints as a match may be problematic; labelling errors might occur; but in 99% of cases the identification makes it an open-and-shut case. And finally - nobody has ever produced a documented match between two different people with the same fingerprint.

Point Taken, however others brought up sexual orientation in the first place as part of the identical twins debate, and I started the thread, so while make no mistake I acknowledge your authority here, and will move the statements, I don’t think I can 'Hijack" my own thread, just my opinion. BTW, if there is any way you can recover and e-mail me what I wrote originally it would be helpful as I spent considerable time on my phrasing.

Since I mentioned it originally - basically I just found it fascinating simply that it points out that two genetically identical individuals who had pretty close to the same environment ended up different - in fingerprints and orientation.

In sufficient degree, this should point out that sexual orientation is neither genetically determined nor due to gross environmental factors (the legendary “meek dad, bossy mom” theory). Like fingerprints.

What was the term used above; “epigenic”?

If you want to start another thread in GD, why not just copy and paste your post?

There have been extensive identical twin studies over the years, including of pairs of identical twins who grew up separated from each other. I don’t know if they studied sexual orientation as one of their data points, if they have however, the statistics would be very interesting.

AllFree

I apologies, I mistook your post immediately after mine for a my post with the big section edited out, I’m sorry I took up your time.

Ignore below:
Because you deleted the part of the post I want to use, the ‘objectionable’ section, so I can’t copy and paste it. That’s why I hoped you had a copy of what you deleted.

AllFree

Nitpick: Not entirely genetically determined, nor entirely environmental. There is certainly at least some genetic component and some environmental component.

Nitpick: “In sufficient degree” If the incidence of sexual orientation being different is exactly the same as the overall population it would argue strongly that there is no genetic connection at all, If the incidence of sexual orientation being different is 0, then sexual orientation is almost certainly entirely genetic.

AllFree

No.

I have no particular expertise on monozygotic twins. However I seem to recall it is the case that mitochondrial DNA varies between twins derived from the same zygote, and also the nuclear DNA can vary based on Copy Number Variations. Both of these factors, along with in-utero and post-natal environmental influences contribute to phenotypic differences. (There are other contributions to differences as well.)

From The American Journal of Human Genetics

Phenotypically Concordant and Discordant Monozygotic Twins Display Different DNA Copy-Number-Variation Profiles

Any differences in the genetic makeup between twins derived from the same zygote represent an irrefutable example of somatic mosaicism. We studied 19 pairs of monozygotic twins with either concordant or discordant phenotype by using two platforms for genome-wide CNV analyses and showed that CNVs exist within pairs in both groups. These findings have an impact on our views of genotypic and phenotypic diversity in monozygotic twins and suggest that CNV analysis in phenotypically discordant monozygotic twins may provide a powerful tool for identifying disease-predisposition loci.

I seem to remember hearing multiple times on Law and Order: SVU (not the best cite I know) that mitochondrial DNA was passed down from the mother, allowing them to determine that someone is related through their female ancestry in the same way that identical Y chromosomes let you determine people are related through their Male ancestry. This would mean that identical twins would have identical mitochondrial DNA. Did they screw it up?

AllFree

I do not know if a TV show got it wrong. Unfortunately my TV viewing is limited pretty much to golf…the question is not maternal inheritance, but whether or not each twin receives “identical” DNA.

More on mitochondrial DNA for monozygotic twins:

Mitochondrial genes in the egg cell have different versions which can be sorted into the embryo in different proportions. When a cell splits into two new cells to form the twins, the mitochondrial DNA is not divided equally between the two cells. So twins that come from a single zygote can have different mitochondrial genes and traits determined by these genes. The mitochondrial genes in monozygotic twins can be as different as they are between dizygotic (non-identical) twins. This can explain differences in identical twins outward appearance as well as personality differences. This is also why it is near impossible for geneticists to test for polar body (half-identical) twinning, as mitochondrial DNA is different in identical twins as well as fraternal.

http://www.sci-ctr.edu.sg/ssc/detailed.jsp?artid=5900&type=6&root=4&parent=4&cat=40

It sure sounds like they got it wrong, my surprise is based on the fact that they have mentioned this multiple times. I would have thought that they would have good technical advisers who wouldn’t let something like that through.

AllFree