I’m not sure what was in question, but if the only question is maternal lineage, mitochondrial DNA would establish that within reason, I think. Most paternal mitochondrial DNA that the sperm manages to get into the ovum is thought to be destroyed, as I recall. However, as the cite I gave you mentions, the maternal mitochondrial DNA itself in the cytoplasm is not exactly the same for monozygotic twins (even when it’s all from the mom).
I don’t think they ever used it in a case other than just one generation, so I must have over interpreted what they said. Thanks for clearing it up for me.
With gratitude,
AllFree
Not only is this not true, it doesn’t even make sense. They use a small clamp on the umbilical cord before cutting it. Nothing is “tied”.
No, that’s not a nitpick, that’s a lack of knowledge of the data. There is, in fact, a higher degree of correlation between the sexuality of identical twins than there is between fraternal twins, thus proving that there’s a genetic component, and the fact that the correlation isn’t perfect proves that there’s a nongenetic component.
Nitpick: It is a nitpick, read the original quote:
"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."
The original poster didn’t know what the degree of difference in data is, and said effectively ‘if’ (i.e. in sufficient degree) it’s high or low enough then that means nature or nurture. The fact that the actual data doesn’t support it is irrelevant, if the data supported it, it would in fact be true, so there was no reason to nitpick the original statement. You could have told them what the data was and let them know that it didn’t support the conclusion though.
First - be careful. The original “identical twins separated at birth” data, used in studies by some British doctor to show that intelligence was heredity not environment, was IIRC shown to be fraudulent and completely imaginary. However, the data itself apparently has become viral well before the internet, buried in many other secondary points that do not adequately reference the original. So any serious “twins separated at birth” stuff has a chance of being bogus.
Second - if the correlation were “1” - all twins are same orientation - then I’m sure we’d have heard about it long before. My solitary data point says no. The interesting thing is that they were NOT separated, and had essentially the same general upbringing (AFAIK) for their formative years. So it’s not strictly nurture. Whether it’s a solitary trauma or a developmental accident - who knows? As mentioned above, maybe a mixture of the above.
But the fact of fingerprints points out that there are variations that happen outside of strict genetic determination.
Third - mitochrondrial DNA is a lot of little rings floating around in the gel outside the nucleus of the cell. The nucleus does an even split, lines up and duplicates itself, so after the split both cells have exactly the same DNA, less minor replication errors. The m-DNA, otoh, as far as I’m aware, does not do any fancy lining-up. I assume from time to time the rings duplicate - they would have to - and so it’s luck of the draw when the cell divides whether a copy of evry ing is on both sides of the divide. Meanwhile, with each division tiny errors creep in, causing differences. I assume the extent to which these rings differ indicates how far removed two maternal lines are…
And since they do not determine gross characteristics, AFAIK, there is not the sme limiting factor of detrimental mutation. If there is an error in copying, the cell still goes on living; whereas serious errors in the chromosomes usually result in a miscarriage?
That would be Sir Cyril Burt Cyril Burt - Wikipedia
Pause for laughter.
Did you really not understand what he meant?
And to top it off, their uncle had 4 kids before he left his wife for a younger man… none of those kids are gay. 
So my personal opinion, based on this and other evidence from reading and listening to people who are gay, is that it is gay is definitely not genetic-hereditary, but it’s not a lifestyle “choice” either, and it’s determined fairly early in life before people are aware of sex and sex roles. So again, like fingerprints, it’s a developmental “happenstance” and not obviously influenced by larger environmental factors.
I had always heard that “innie” or “outie” (navels, that is) depended on how the umbilical cord was tied.
Maternal (Mitochondrial) DNA can provide evidence far beyond a single generation. DNA matching (in the forensic sense) provides a statistical measure of similarity based on number of well defined loci on the DNA strand. This does not mean that the DNA is identical on a base pair level. Intergenerational variation is enough to produce the changes in expression observed but DNA matching will still identify the matrilineal line for many generations. DNA replication is pretty good, but it is not perfect. However, the rate of variation in DNA is pretty constant (statistically speaking), and has been used to define a DNA clock, giving the concept of Mitochondrial Eve, the mother of us all. The same concept applies to the patrilineal Y chromosome, which can be used to identify the descendants of Ghengis Khan (about 8% of Asian men). This spread is probably based somewhat on selection, rather than just random growth. There is also Y-chromosomal Adam, who lived somewhat later than Mitochondrial Eve.
In other words, when a TV show claims that maternal DNA is passed on identically, it is only identical in a statistical (forensic) sense, not at the base pair level. These variations accumulate over generations and produce phenotype variation, but the line can be traced over the generations. Hope this helps some more.
Si
I wish I had introduced myself in a dozen threads when I was first new!
I do agree with the ad: Crown Royal Cask No. 16 is the finest CR finished in cognac oak casks. 
In case someone is wondering about this post, it refers to a new poster who posted the same message to a bunch of threads, which have now been deleted.
Thank you very much, I found this very helpful. I was wondering, since you seem knowledgeable about the subject. Do scientists view the natural alterations that occur in normal DNA replication as something that evolution finds beneficial and perhaps even has a preferred alteration rate that is different from simply the natural error rate from replication?
To clarify, 8% of Asian men are descended from Genghis Khan in the strictly male line. So in other words, for 8% of Asian men, if you look at their father, then their father’s father, then that man’s father, and so on, eventually you’ll get to Genghis. 100% of Asians are descended from Genghis Khan somehow or other, but for the other 92%, it’s something like father’s mother’s mother’s father’s mother’s … father.
Interesting. I never knew this. Here’s a related Wiki link for those that want to learn more: Family and descendants of Genghis Khan - Wikipedia
I am not an evolutionary biologist, so I can’t really respond. And I am not sure about what you are asking? The error rate is the error rate - DNA replication errors, chemical errors, radiation error - these all contribute. In the other hand, cells have a variety of mechanisms to repair damaged DNA or discard corrupted material. So there is no mechanism for a preferred alteration rate.
And evolution has no preferences - errors in DNA replication have a benefit, or not, and sometimes those benefits provide long lasting changes, and sometimes they don’t. And some deficits hang around for a long time, too. Environmental changes influence evolutionary paths as well. It is all apparently random (in the evolutionary world - I don’t agree entirely with evolutionary theory and its conclusions, but I’ll present the science as I understand it).
Si