(A/N: This is just a silly fic idea that I thought about when I was studying inheritance. So hopefully this wasn't too confusing T-T... p.s. I LOVE TUTOR SATAN!!!)
It was a quiet day in the Devildom, no plans for the weekend. Everyone seemed to be busy doing their own thing or relaxing. That's when you decided to check what your favorite demon, Satan, was up to. When you approached his door, softly knocking, there was no answer. Which eventually led you into quietly turning the doorknob and taking a peek to see if he was inside.
And there he was. You noticed immdiately once you poked your head inside, the quiet murmuring of Satan's voice, low and lost in his own thoughts, as if he was talking to the book in his hands. You smile gently and stepped into the room, carefully taking your steps to avoid knocking over the piles of books that were on the floor and not wanting to alarm him. He still didn't seem to notice that you were there.
"If the alleles were heterozygous," he mutters, flipping a page. "That would give a three-to-one phenotypic ratio...unless the recessive allele—"
"...Satan?"
He freezes, shoulders tensed up as he remained still on his bed. He was faced towards his window before slowly turning his head around to face you. You noticed a faint hue of pink growing on his cheeks as you caught him in the act of talking to himself.
Satan clears his throat, closing his book slightly but still leaving his thumb in between the pages, "I didn't realize you were there."
"Sorry, I knocked but you didn't answer, so I checked to see if you were here. I didn't mean to startle you." You began, studying his slightly flustered face before your eyes shifted to the book that he was holding, "what're you reading?" You tilt your head, stepping closer.
For a moment, he stares at you, looking like he might pretend that nothing happened. Then he exhales, fingers opening the book again to the page where he left off. He looks down at the book on his lap, "Genetics," he admits. "Well— Inheritance, to be precise."
You take a seat beside him, leaning over to take a look at the page. It was some crazy diagrams of squares with random alphabets, and the mentioning of a farmer named Gregor Mendel, with a photo of a ton of pea plants.
That only made you more curious. "Inheritance of what?"
His gaze drifts away again. "Just...Traits."
There's a pause. A very deliberate one, like he was lost in thought, hiding something. Which was very unlikely of Satan since he was always ecstatic to share what he read in his books.
"You were calculating something," you say gently.
Satan hesistates for a bit, refusing to make eye contact with you. Then he lets out a resigned huff. "I suppose there's no point in denying it now." He begins, tapping the page with one finger, pointing to a specific paragraph in which your eyes immediately followed his direction to the text. "I was reading about how traits are passed from parents to offspring. They were talking about alleles and how the phenotype would be different depending on whether the two alleles were dominant, recessive, heterozygous or homozygous. But still, a lot of factors can play into it."
Satan responds, looking up to see your expression.
You blink and stare blankly at the page. "...Okay. I'm already lost." You admitted, defeated with the information that was dumped onto you.
That earned a small, fond smile from Satan, almost relieved.
"That’s alright," he says, softening his voice. "Let me explain it better.”
He turns the book so you can see the diagrams, though he doesn't expect you to read them. "For most traits, each parent carries two alleles. To put it simply, the alleles are different versions of the same gene. One from each of their own parents."
You nod slowly at his explanation and he checks your face before continuing.
"Some alleles are dominant, meaning that they're expressed in the phenotype even if only one is present. Some alleles are recessive, meaning that the phenotype will only appear if both alleles are the same."
You put a finger up, causing him to pause for a moment. "Sorry, wait. What are phenotypes?"
Satan smiles gently at you before explaining, "they're a set of observable traits. So for example, the genotype is the specific set of alleles you carry, and the phenotype is how those genes are expressed, like your hair color, eye color, or blood type."
You nod slowly, eyebrows furrowing a bit but slowly getting the concept.
Satan continues, "So, back to the alleles, if a parent carries one dominant allele and one recessive allele, which is what we call a heterozygous genotype, only the dominant trait will show. But they can still pass the recessive one on." He explains, "For example, in simplified models, curly hair is often treated as dominant over straight hair. So if the child inherits the curly hair gene from one parent, they are most likely to have curls or waves. But genetics like these are quite complex since they involve multiple genes and factors like 'incomplete dominance' or can be influenced by the environment."
You hold up a hand again, "woah woah, slow down a bit. What in the world is incomplete dominance?"
"Incomplete dominance is simply when neither alleles are dominant over the other, so they would result in a heterozygous offspring with an intermediate phenotype." Satan explains, but the look on your face told him that you were still confused.
"Let's say if a red flower and a white flower were to be crossed, the resulting flower would be pink because neither alleles from the parents were completely dominant over the other."
"Okay, I think I kind of get it now." You responded and he smiles, reassuring you that you were doing great.
Satan continues explaining the concept, "If both parents are heterozygous, there's a seventy-five percent chance the dominant phenotype will appear, and a twenty-five percent chance of the recessive one."
You hum in response, before coming back to your previous thoughts. "Wait, if there are so many genes that make up our traits, what were you calculating probabilities for earlier?"
Another pause. You noticed a heavier hue of pink grow on his cheeks as his eyes darted elsewhere, avoiding yours.
"Satan." You say teasingly, a grin growing on your face as you realized what he was doing earlier.
"You were calculating what our hypothetical child would look like, weren't you?" You teased.
Satan's face completely heats up, bright red as he scoffs. "That's… a highly accusing inference..." he stops, and then sighs. "But I guess you weren't wrong."
You laugh, reaching out to lightly touch his arm, "You're cute when you overthink."
He looks away, but he doesn't pull back. "For what it's worth," he adds quietly, "many traits are polygenic, meaning that traits like height, skin color, and hair texture are influenced by multiple genes. So they're far too complex to predict accurately. Not only that, the environment also plays a significant role as well."
You smile. "So basically... you can't actually know."
"Statistically speaking? Yes." He closes the book at last. "But that doesn't make thinking about it any less... interesting." He admitted.
You smiled, leaning gently into his space. "You're adorable."
