Chapter Text
Genetics is a field of biology which discusses variation and heredity – the similarities and differences among organisms and how these characteristics are transmitted through generations. The Father of Modern Genetics, is Augustinian friar Gregor Johann Mendel. His study involving Pisum sativum, commonly known as garden peas, led to the discovery of the fundamental principles of genetics.
Characteristics are determined by a pair of factors called alleles. There are typically two types of alleles: dominant alleles and recessive alleles. In Mendelian Genetics, if even a single dominant allele is present with the pair of alleles designated to an organism, it will mask the effect the recessive allele provides.
These alleles are located in the chromosomes.
-
“I’m homo, remember?”
“Homosexual?” Sari glared at Renji who simply laughed and apologized. “I’m sorry, that was rude of me. But I don’t care about stuff like hetero or homozygosity, remember? Fuck genetics, really, I hated that subject.”
“...Are you sure you want to marry me?” She muttered, finally speaking after what seemed like an eternity. The concern and panic was evident in her voice. “If we ever have kids, there’s a hundred percent chance that our sons—”
“—will be loved and cherished deeply,” Renji cut her off, “no matter how they turn out. It applies to our future daughters too should ever we be graced with them. I am a botanist, love.” He said with a smirk. “I took up at least the fundamentals of genetics during my undergraduate days, I know what I’m getting myself into. And yet I’m still here, on my knee, asking you to marry me.” He kept her gaze this entire time to convince her that he means every single word, his dark blue eyes stayed entirely focused this entire time.
“I don’t think I can—”
“Sari,” she calmed down instantly, “remember we dated years later after I found out? I fell in love you during that time, and I’m still here today, right? What makes you think I’ll leave if our son ever happens to be like you? The only concern I have about children is what to name them.”
She laughed; he’s got a point.
Renji smiled, his hope levels rising by the moment. “Then, I will ask you again. Sari, love, will you marry me?”
-
There are two types of chromosomes present in humans: autosomal chromosomes and sex chromosomes.
Sex chromosomes primarily determine the sex of the organism. However, some characteristics are determined by the alleles linked to these chromosomes. This mode of inheritance is a form of Non-Mendelian Genetics, wherein the rules and expectations in typical genetics don’t apply.
In humans, there are two types of sex chromosomes: the X and the Y chromosomes.
-
“Yes.”
-
Males have one of each type, an X and a Y chromosome. Females, meanwhile, have two X chromosomes.
Offspring are formed by the fusion of gametes: the egg from the female, and the sperm from the male. It is through a process involving two successive nuclear divisions (meiosis) that these gametes are produced. As a result, the gametes possess half the genetic material of original cell.
For males, half of the gametes would possess the Y chromosome while the other half would possess the X chromosome. Female gametes would all possess the X chromosome.
-
“He has your eyes.”
“Oh dear god, don’t remind me.” Sari groaned. “I never wanted my kids to have the problems and discrimination I faced.” The bed being tilted was the only thing keeping her up after all those hours of labor. Never again, she swore to herself. I love Renji, I really do, but I don’t think I can handle another pregnancy.
Renji chuckled. “Come now, love, times are different now. Besides, you’re a successful person in your field despite natural selection favoring against you so why do you think so negatively of our little peanut? Also, look,” he tilted their child in his arms, who had his eyes open just enough to see they were indeed the exact copy as his mother’s, “ain’t he the cutest?”
Sari smiled and reached over to stroke their child’s cheek with her finger.
“He sure is.” She whispered in utter adoration.
This was their boy, their beloved son.
-
Sex-Linked Inheritance is a type of Non-Mendelian Genetics wherein the alleles are linked to the sex chromosomes. The alleles could be either linked to the X or Y chromosomes.
If the mutant allele is found on the Y chromosome, all the male offspring of the affected male will exhibit the mutant trait. If it’s found on the X chromosome, however, the frequency of variants of offspring all still depends on whether the trait is due to a dominant or recessive alleles.
Males are more susceptible to X-linked recessive traits because they only have one X chromosome. If that chromosome has the mutant allele, from either an affected or carrier (heterozygous; possessing a dominant and recessive allele) mother, then it will manifest itself accordingly.
-
Their little, precious Tobio.
-
-
-
Is he tired?
“Now, let’s see if you understood what I just said.”
Oh, he is, Tobio realized. Tsukishima’s tired.
Presently, all five second year Karasuno Volleyball Club members were at a booth in a café not too far from their school, studying for their upcoming exams.
Well, Tobio adjusted himself in his seat, we have been here since morning and it’s nearing dinnertime already. We should probably order cake or something for him. He likes strawberry shortcake, I remember. This café doesn’t have it, though. I don’t know any place where there’s good strawberry shortcake nearby... I can ask oma for a recipe—
“—Are you listening, King?”
Tsukishima’s voice snapped him out of his thoughts. Going back to reality, Tobio noted everyone looking at him. Hinata and Yamaguchi were simply looking at him, Yachi-san looked concerned, while Tsukishima looked annoyed—
—tired.
“Well?”
“I understand this lesson.” Tobio nodded towards his notebook. “I paid attention in class during this lesson.”
Tsukishima sighed. “Thank god.” The middle blocker flipped a page in his notebook and began reading. “Well then, if a red-green colorblind female mates with a normal male, what is the probability that they’ll have a normal female? Hinata, answer.”
“Uh…” Hinata pondered over it for a moment before breaking into a grin and stating confidently, “One.”
“A colorblind female?”
“Uhhh... zero, right?”
"Congratulations. King, what’s the probability of them possessing a normal male child?”
You are going to be dubbed the biggest idiot in the world, he thought, if you aren’t able to answer this one correctly.
Inhale. Exhale.
“Zero.”
Tsukishima looked up from his notebook and stared at him. “And a colorblind male?”
Tobio looked down at his notebook, for some reason unable to look at the middle blocker directly in the eyes. His notes on Sex-Linked Traits looked back at him.
Inhale.
“One.”
Exhale.
-
-
-
Red-green colorblindness in humans is an X-linked recessive trait.
-
-
-
Ding-dong!
They only had to wait literally a few seconds before the door opened, revealing a bouncing middle blocker with an amused captain behind him.
“I didn’t realize this was your house, Hinata.”
Hinata stuck his tongue out at him. “Boo, Tsukishima! Daichi-san allowed me!”
“Did he now?”
“He did!”
“I find that hard to believe.”
“Anyway!” Hinata jumped high in the air, grinning like the ball of sunshine he is. “You made it! We were beginning to think you weren’t going to show up!”
“Tsukki accidentally forgot his exchange gift when we were a street away so we had to go back and look for it.”
“Yamaguchi.”
“Sorry, Tsukki!” Yamaguchi laughed, however, showing just how sorry he really was. Kei rolled his eyes but followed his friend in the house anyway. They nodded to their captain who greeted them cheerfully and led them to the living room where everyone else was waiting.
“We haven’t eaten yet.” Daichi-san said. Hinata had already went ahead of them, saying something about him being next at a game of some sort. “Kageyama and Suga went out a few minutes ago to grab plates from Suga’s house at Yachi’s insistence on not using disposable utensils. We actually thought you were them.” Nishinoya-san, Narita-san, Kinoshita-san, and Ennoshita-san (with full unnecessary support from Tanaka-san) were playing against each other in Mario Kart while everyone else was watching and laughing.
“This is Suga you’re talking about, Daichi.” Asahi-san said, smiling wryly. “If Suga is aware that our parents aren’t home, he’ll just walk in.”
Sawamura sighed. “I was hoping since Kageyama is with him...”
“He might just corrupt Kageyama, you do realize.”
Kei wants to say something about that, but decided that it wasn’t worth the hassle. He sat down at the end of the couch, leaving space between him and Yachi-san. He sent a smirk in Yamaguchi’s direction who pointedly ignored him and simply began conversation with their first-year manager as soon as he sat down in the only remaining seat in the entire room. The atmosphere was warm and enjoyable, Kei found himself relaxing and enjoying the stay.
It was three rounds later when the door suddenly opened and a voice called out “I brought the beer!”
Even Kei cracked a smile while everyone laughed, Asahi patting Daichi’s back, when Daichi let out a groan and covered his face in his hands.
“Suga-san, I thought we were carrying the utensils.”
“Haha! Kageyama, you look shookt. It was just a joke since I knew Daichi’s parents aren’t home.”
“Ah, sorry.”
Moments later, the two setters entered the living room, Kageyama a few paces behind.
“We got the plates! I also found utensils and cups for everyone. I even brought extra in case Tsukishima and Yamaguchi—oh, they’re here!”
“They arrived not too long ago.” Daichi-san stood up and motioned to the kitchen. “I’ll take them to the kitchen and heat up the food while I’m at it.”
“I’ll wash the dishes.” Kinoshita volunteered. Suga-san and Kageyama handed the boxes they were holding to the two
“We’ll be right here then, enjoying ourselves in the living room.” Suga-san made a show of getting comfortable in Daichi’s old seat. Kei was about to move for Kageyama to sit in the sofa with them (he figures he can be kind once this Christmas, even to the King) but stopped when Suga-san waved Kageyama to sit next to him. Okay then, Kei made himself comfortable again when Kageyama settled on the armrest of the couch Suga-san was sitting on.
“Don’t break anything.”
“How rude!” Suga-san pouted briefly before seeming to remember something. “Oh yeah, I found my UNO cards at home!” He took out a small box from his bag. “Anybody want to play?”
“I want to play!” Nishinoya exclaimed, always game for anything this guy.
“How many decks did you have?” Yachi-san asked.
Suga-san smirked. “Three. And I brought all of them~.”
“That’s going to be a shitton of cards.” Ennoshita-san said with an amused upturn on his lips. “I’m in.”
“I heard of that game but I never got the chance to play it before.” Hinata said, looking in awe at the cards Suga-san was holding. “I want to play!”
“I can help you, Hinata.”
“Oh! Thank you, Yamaguchi!”
“Shimizu, want to play?”
“I think I will help Sawamura heat up the dishes. But have fun for me, though.”
“Mkay! Who else is playing?”
Apparently everyone else sans Kei, Suga-san, Yamaguchi (since he was helping out Hinata), and Narita-san. Kageyama was hesitant at first but Kei noticed he looked determined after Suga-san said something to him, if him taking a seat on the space diagonally across the older setter were to say anything.
Huh.
As soon as the cards were dealt, Kageyama turned to Suga-san who began pointing to the cards, whispering in soft volumes, with Kageyama seemingly paying close attention. Kei was closest to them but even he found difficulty in catching a glimpse of their conversation. Thinking it was too much of a hassle to speak up, he said nothing.
Good thing for Kei, Nishinoya-san is a nosy little shit that also noticed the exchange.
“Suga-san, what are you doing?”
“Ah,” Suga-san glanced at Kageyama, “I’m helping Kageyama sort his cards.”
Ennoshita-san spoke up. “Is this your first time playing, Kageyama?”
Kageyama shook his head. “No. I played before with my cousins, but I would always still ask for help.”
“What’s this, the King getting special treatment?” Kei couldn’t even stop the retort if he even tried. “Even the King has weaknesses, huh? Need us commoners to help you out?”
“Tsukishima—”
“Yes.”
The fact that he said it so nonchalantly and with such innocence was enough for everyone in the room to pause and stare. Kageyama paid them no mind and just focused his look to Kei.
“I need help in playing UNO. I hope none of you are against it.”
“Of course they’re not, Kageyama.” Suga-san to the rescue. “Come on, let’s start the game now, okay?”
When Daichi has called them to the kitchen much later, they weren’t close to finishing the game.
Suga-san appeared to stick close to Kageyama the rest of the night.
Kei brushed it off and tried to ignore them.
Keyword being try.
-
“We planned to spend the entire lunch period in the library today, are you sure you don’t want to eat anything?” Yachi-san asked, looking worriedly at Hinata. Karasuno High School is approaching their final examinations period so our beloved first years decided to take initiative and studying together (aka helping HInata and Kageyama). Today they agreed to work in the library.
Hinata waved her off. “I’ll be fine, Yachi-san! I’m tougher than I look!” He began walking at a faster pace to the library, rambling about how he wasn’t hungry anyway and that they should hurry because Stingyshima and Yamaguchi are probably already waiting. Tobio, walking in step with Yachi-san at a relaxed pace behind Hinata, shared a look with Yachi-san.
“He won’t last the whole period.”
“That is true.”
Almost in sync, they took a bite of their sandwich they had the hindsight to bring that day.
Ten minutes in, Hinata let out a groan. He then suddenly stood up, loudly whispering, “I’m going out to buy food!”
Hinata lasted longer than I thought, Tobio thought, finishing up his math homework. Yachi-san nodded encouragingly at his side when he boxed his final answer. They had a small square table to themselves in the middle of the library. Tobio and Yachi-san occupied one side of the table, Hinata was previously seated to their right, Tsukishima to their left, and Yamaguchi across, but had shifted closer to Hinata to help him in his English assignment.
“You got it. Good job, Kageyama.”
Kageyama nodded, feeling proud of himself. “Thank you.” Promising to Ennoshita-san about not sleeping in class sure has made it easier to catch up to the lessons.
Yamaguchi then stood up, holding up his wallet. “Ah, wait Hinata, I’m also kinda hungry so I’ll go with you. Anybody else want anything?”
Tobio gave Yachi-san a pointed look, but she pretended not to see. “A snack sounds good right about now.”
“Want me to buy food for you? Anything you want in mind?”
“Yamaguchi is such a gentleman now, huh?”
“Tsukishima.”
“Sorry, ‘Guchi.”
Tobio coughed to hide his laughter, but it wasn’t effective since Yamaguchi still glared at him too and Yachi-san pinched his arm underneath the table. He does not regret it though, especially when Tsukishima raised his head from his readings and smirked at him.
Yachi then stood up from her seat, “I’ll just come with you.” She smiled at Yamaguchi who smiled back. Tsukishima made a face and Kageyama hid his smile behind his notebook.
“Blegh, I’m third wheeling again—ouch! Yamaguchi don’t pinch me!”
“Quiet, we’re in the library,” was all the freckled crow said as he walked in the direction of the library exit. Yachi was giggling as she and a grumbling Hinata walked behind Yamaguchi. Tobio rolled his eyes and searched through his bag for his red pen.
…Ah, Tobio paused and stared off into space, I forgot to get it back from oma last night.
“Need something, King?”
Tobio blinked. So apparently when he stared off into space, he was staring in Tsukishima’s direction. Duly noted. He didn’t let it embarrass him though, clearing his throat.
“Can I borrow a red pen?”
Tsukishima raised a brow. “What for?”
“I left mine with oma last night and I need a red pen to do my English homework.”
“It’s right in front of you.” Tsukishima motioned to his pens spread out in front of him.
Tobio moved to get it but stopped. Tsukishima has a lot of colored pens.
“Tsukishima, can you hand over the red pen?”
To Tobio’s surprise, Tsukishima sighed but otherwise lifted up the pen—the one closest to Tobio—without any further complaints. “Here, King.”
“Thank you, Tsukishima.” Tobio hoped his voice was as sincere as how he feels. Tsukishima merely grunted and went back to his homework. The setter smiled and also began his homework.
Sometime later, Tobio accidentally nudges Tsukishima’s foot. He immediately pulled back and muttered an apology when Tsukishima snapped his head towards him. Not even half a minute later, Tobio felt a nudge on his own foot. He quickly turned to Tsukishima who was, surprise, smiling almost fondly at him.
“Not sorry,” were the last whispered words between them for the remainder of their stay in the library. Their feet every so often nudging the other.
“So...Kageyama—”
“Shut up, Yamaguchi.”
“Haha. Sorry, Tsukki.”