While taking a shower last night and thinking of eva, an idea came to me. It was interesting how Fuyutsuki told Shinji that Rei had been made from Yuis' data. What exactly did that mean? Now this will be some rabbit hole speculation so here goes.

1) Rei was made from Yuis' data.
2) Gendos plan involving Rei and Shinji getting closer.

I'm thinking that w/e "data" means is more than just DNA, like the way Naokos' self was split and placed in the magi, but in this case it'd be certain traits of Yuis personality that were transferred to Rei. That would explain why Shinji was drawn to her (he compares her smell to unit1 and his mother) and from Rei, the desire feels warm together with Shinji and Gendo. It also make more sense of Gendos plan to awaken Unit1, he killed 2 birds with one stone. Shinji saw his mother in Rei and Rei would've had Yuis' protectiveness towards Shinji. So like the title says, just how much of Yui is Rei made of?

I guess the answer to that question also depends on how much of Lilith is in Rei. Aside from having Lilith's soul, Rei also has some of Lilith's DNA in her too, but how much is the question. Is it mostly Yui DNA and some Lilith DNA, mostly Lilith DNA and some Yui DNA, or an equal mix of both? Rei and Yui might only be related to each other in the sense that they are both human. If you go far enough back, every human is technically related because they are all part of the same species. Rei might have been given enough of Yui's DNA to give her a human form, but not enough to make her closely related to her in a familial sense.

Here's a mind blowing fact, humans actually share 60% of the same DNA as bananas, but despite that huge percentage the two look nothing alike. That just goes to show how small a portion of our DNA actually contributes to things like genetics and familial relation. All humans share 99.9% of the same DNA with each other, so in the broadest sense Rei is related to Yui because they are both human, just as she and Shinji are both human. The closer that 99.9% is to 100%, the more closely related two people are, so familial relation all comes down to that last 0.1% Rei could have 99.9% of Yui's DNA in her, that being the part that encodes for a human form, but that remaining 0.1% that would make her actually related to Yui and Shinji is instead composed of DNA from Lilith. So in this sense, Rei is technically mostly Yui (99.9%) like all other humans would be, but is also not Yui because the last 0.1% that encodes for genetics and familial relation belongs to Lilith, hence the blue hair and red eyes, traits which Yui did not have. So essentially, Rei is Lilith in a Yui-shaped shell, but not a Yui-colored or Yui-composed shell.

"Rei has Lilith's DNA" is NGE fanon, as best I can determine. The show doesn't provide a direct statement, but every supplemental source that says anything calls Rei a "copy" -- the same word that's used to describe what the Evas are to Adam. Furthermore, Rei's origins aren't tied to a transgenic experiment the way that Kaworu's are. The first Rei's origins are frequently explained, using the information provided to us in the show, as "Nerv tried to reshape a body from Yui's LCL and usher her soul back inside; but they got the wrong soul". It's explicitly Yui's physical form that was being reconstructed, and the entry plug would prevent random "seepage of Lilith DNA". Rei is best explained as a palette-swapped clone -- a trope that's used elsewhere within NGE itself (see: the Evas). Explaining Kaworu's status as a half-Adam, half-Lilin genetic hybrid despite HIM being in practical terms a palette-swapped clone is annoying enough, but at least with him one can still fall back on him being a child of Adam and thus perhaps possessing some limited version of Angel morphic adaptability. (Insert mental image of super-creepy baby Kaworu here.) Rei? How do you explain her? "Lilith DNA" doesn't provide anything useful here, in my opinion -- it just hampers, really.

And here, we're specifically talking about NTE, to boot. In the movies, all we've been told about Rei is that she's a replica of Yui. "Replica" doesn't in any way suggest genetic hybridization; a replica is a copy, i.e., a clone. Lilith's involvement is a complete unknown at this point, as well, but the odds don't look good. The storyboards for Q suggest that Rei is simply manufactured in a factory in the Nerv facilities. Since mass production is taking place in HQ, they would need to be utilizing just the head if anything, since the body is quite a distance away -- but Lilith's head is sitting in the dilapidated command center on a bed of FoIs with no measures taken to access its biomass.

it is kept deliberate vague, meaning it is what you want it to be, that said Rei is seen reading a book that is a cross between genetics and parabals it probably has to represent metaphysical biology, this is a niche subject, it could simply be Rei trying to figure out what she is meaning she doesn't know it herself or she inherits some of Yui's intrest.
I also think her genetics fluctuate for a better term. Rei spends weeks/months revalidating from her injuries then near the end she drops a arm and instantly regenerates a new one. I also believed that during the activation test Rei would have used her own AT field to protect herself if she could,meaning she was not capable at the time. So stuff changes and that probably true on a genetic level

@orcot: This is a thread about the films, not the original anime.