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Now, I'm not saying that I'm a die-hard DFO believer. I think that the theory is fun, and as a joke, I told my friend that if Izuku's father wasn't introduced by the end of the manga then DFO was officially canon by process of elimination. I'm just here to give my opinion about one of the main points people claim disproves DFO: Izuku being born quirkless. I would argue that Izuku being born quirkless, rather than having his quirk stolen as an infant, gives more credibility to the DFO theory.
For starters, when Izuku is told he in the first episode by the doctor (who is obviously AFO's doctor) that he's quirkless and is shown the x-ray of his foot, the doctor says a line (and I'm paraphrasing here) about how "it was virtually unheard of for a child born from two fourth-generation quirk users to be quirkless." The doctor could potentially be lying, but that is very unlikely. Even if he's evil, there's no reason for him to lie in that scenario: Quirks have been around for over a century by then, and lying about something that could be so easily disproven would be moronic.
So, with the belief that he was telling the truth, then it gives more insight into how quirks work. Quirks, in some way, shape, or form, are genetic. It's why quirk marriages were a thing. It's why Katsuki was the unbelievably lucky mix of both his parents' quirks, allowing him to make explosions. It's why Tsuyu's whole family looks froglike. Quirks aren't magically bestowed upon people like Celestia with visions: it's passed down genetically. Quirks are formed from a genetic mutation. This means that based on what the doctor said, quirks are a dominant allele.
To give a basic recap in biology: each gene has two alleles, one from each parent. Genes are what give you your appearance and more: whether your eyes are blue or brown. If you'll be blonde, brunette, or end up as a redhead. If you are more susceptible to different health problems like stroke or Alzheimer's. Alleles, on the other hand, can be either "dominant" or "recessive." "Dominant" alleles need only one parent to transfer it to the child for the trait to show up. "Recessive" alleles, on the other hand, require the allele from both parents to show up in the child. For example, curly hair is dominant over straight hair. If you use 'A' to describe the allele for curly hair and 'a' to describe the allele for straight hair, then it could be looked at as this:
AA= curly hair
Aa= curly hair (dominant allele present)
aa= straight hair (both recessive alleles present)
This means that quirks show up when through a dominant allele. The mention of "fourth-generation quirk users" implies that two quirked parents can give birth to a quirkless individual. That wouldn't be possible if quirks were a recessive allele. Therefore, if both of Izuku's parents were fourth-generation, then it is technically possible for Izuku's ancestors to have passed on the recessive quirklessness through the generations. And Izuku just happened to be the unlucky son of a gun who lost the genetic lottery.
But do you know what this means? It means that it doesn't disprove DFO in the slightest. In fact, having a parent who is a first-generation quirk user adds to the credibility. Canon shows that AFO was the first person who had a quirk. While Izuku is still unlucky on his mother's side of the genetic lottery, having a dad who automatically has a recessive allele makes his quirklessness much more likely.
In conclusion: Izuku being born quirkless just adds to the Dad for one theory. Thank you for coming to my TED Talk.
All I’m saying is that it would make a lot of sense if All for One was Midoriya’s dad...like I haven’t read the manga or anything but guys
His dad is gone (which isn’t like a big thing but he doesn’t have a dad rn ok)
That doctor guy??? The doctor that told Midoriya that’s he’s quirkless is the doctor who makes the nomu
Also totally different thing but I’m all for the theory that the nomu with wings was Midoriya and Bakugou’s old classmate
The creator of bnha likes Star Wars and puts stuff in bnha all the time (I saw a TikTok on it but like apparently the beach Deku cleaned was the name of something in Star Wars???)
But yeah so the whole I am your father thing is definitely something a Star Wars fan would recreate ngl
Also the fact that All for One was like a first generation quirk user right?? Or at least really close to first gen so it would be much more likely that his kid would be quirkless
And if he did marry Inko for more endeavor like reasons (quirk ones)...he could have been looking for a kid who could take quirks without touching someone
Cause Inko’s quirk attracts stuff
...i just think it’s neat to think about
Listen all I’m saying is that if Dad for One was canon does...does that make Kamino an over glorified custody battle