"Of course we can check your chromosomes!" Xia Linfei looked at Su Yuan curiously. "What got you interested in that all of a sudden?"
"Nothing. I just got curious."
What Su Yuan was really curious about was whether the chromosomes in her body were XX or XY. If they were XY, then from a genetic standpoint, she'd have a lot to worry about. Her current appearance might be a false phenotype, and science had no explanation for anything so bizarre.
But if they were XX, then at least her outward appearance and genetics would match, and there likely wouldn't be any more changes. That result might dash her hopes of regaining her "male body," but at least she'd have a definite answer and know what direction to take with her life.
So as soon as she heard they could check chromosomes here, Su Yuan felt an immediate urge to do it.
"The human body has twenty-three pairs of chromosomes: forty-four autosomes and two sex chromosomes. Males have XY sex chromosomes, and females have XX. During reproduction, males undergo meiosis and produce either X-bearing or Y-bearing reproductive cells, while females can only produce X-bearing reproductive cells."
"I know that. Men provide either X or Y sperm, while women provide X eggs. If the fertilized egg is XX, it's a girl; if it's XY, it's a boy. So aside from a few exceptions involving female exclusion, the sex of the child is actually determined entirely by the man, since only men have Y chromosomes."
Xia Linfei nodded with a smile. "Good thing you study biology. You picked it up easily."
"Since you're curious about chromosomes, and I happen to be researching human genetic polymorphisms, why don't you contribute a sample to my project?" Xia Linfei suggested.
"Use my sample?" Su Yuan hesitated.
She had to be careful about this. Her transformation was already bizarre enough. She could assume aliens had tampered with her, but Su Yuan was more inclined to think there was something wrong with her genes. The human body had around three billion base pairs and nearly a hundred thousand genes. So far, the Human Genome Project had found around twenty-five thousand genes, far fewer than the expected hundred thousand.
But who knew if her genetic information contained a gene that caused sex changes?
If it did, its discovery could cause serious trouble.
"Don't want to?" Xia Linfei raised an eyebrow and smiled. "For this genetic polymorphism project, my advisor, a few senior students, and I collected over ten thousand samples from the public. One more won't make a difference. What's there to be reluctant about?"
Su Yuan was still uneasy, so she pretended to be curious and asked, "What exactly does genetic polymorphism research involve?"
"Simply put, the genes that control a trait aren't always exactly the same. Genetic codes need to be transmitted with a certain degree of accuracy, but there's also some flexibility. Different groups adapt to different environments, so even genes that produce the same trait aren't necessarily identical. The trait can stay the same even when the DNA fragment's length differs, when the repeated DNA sequences differ, or when individual scattered bases differ."
"For example, take the genes that control single or double eyelids. Even if they all express as single eyelids, those genes might not be completely identical."
Su Yuan nodded. "I think I understand. The useful information carried by a gene is the same, but the noncoding regions of the DNA, or the regions without important functions, can mutate because of environmental factors, making them different."
"More or less." Xia Linfei gave her an approving look. "These variations might be caused by the deletion, repetition, or insertion of individual bases, changing 'restriction endonuclease' sites and thus altering the length of the DNA. The copy number of repeated sequences might also vary. Or individual scattered bases might be deleted, inserted, or replaced."
"Our project is to study the distribution patterns of genetic polymorphisms caused by these three conditions."
"So you compare specific genes?" Su Yuan asked.
"Exactly. We mainly chose the genes that control single or double eyelids, hair color, and whether someone has attached or detached earlobes."
"I thought you were checking all my genes!" Su Yuan breathed a sigh of relief.
Xia Linfei patted her on the shoulder and laughed. "Check all your genes? Do you think we're the Human Genome Project? Several countries worked together for years to complete that. Even though our research group is only studying three genes, we have to split everyone into three teams to work on them at the same time, and it's still a huge amount of work."
"I didn't know that at first!"
Su Yuan couldn't help laughing at herself. Human genes were incredibly complex. Analyzing polymorphisms in just three specific genes was already a massive project, and she'd been fretting that some unknown gene might be exposed. It was almost laughable.
Genes couldn't easily be observed with the naked eye. Xia Linfei's project only targeted three specific genes. The other genes were completely beyond its scope.
It made sense for a layperson not to know, but she'd been worrying over nothing herself.
"You were curious about chromosomes, right? If you give us a sample, your big sister here can arrange for you to take a look at your own chromosomes!"
"Won't that be a lot of trouble?" Su Yuan thought of how heavy Xia Linfei's research workload already was. Would her "curiosity" add to it?
"Don't worry. It's just a little extra."
Since Xia Linfei put it that way, Su Yuan didn't refuse.
Seeing this, Xia Linfei brought over a lab chair, stood on tiptoe, and took a disposable blood-drawing needle and two blood sample tubes from the cabinet above.
Seeing the needle and the two blood tubes, Su Yuan's eyes widened. She stammered, "Y-you need to draw blood, too?"
"How else would we get your genes? Come on, roll up your sleeve."
"I thought skin cells or cells from inside the mouth would do." Su Yuan muttered, but obediently rolled up her sleeve.
She wore a long-sleeved, pale purple casual shirt. It was a wonder she could stand wearing it in such hot weather. No wonder she was always heading to the air-conditioned library.
"It's necessary for the experiment. We're using peripheral blood."
With the sleeve rolled up, her fair, smooth skin was exposed. Xia Linfei glanced at it and complimented her. "Su Yuan, your skin is so fair."
Su Yuan chuckled and closed her eyes. "Go ahead."
Xia Linfei tied on a tourniquet and gently patted the crook of her arm. The sharp needle came closer.
Su Yuan suddenly opened her eyes. "Wait! Sister Xia, are you good at drawing blood? Can you get it on the first try?"
Xia Linfei was instantly annoyed. "Don't you know I used to study at a medical university? Drawing blood is easy! Your arm is so fair, and your veins are pretty clear. I guarantee I'll get it on the first try!"
"Oh." Su Yuan felt a small prick. With her eyes open, she watched the bright red blood flow through the needle, quickly filling both sample tubes.
"Done."
"What happens next?" Holding a disinfectant cotton ball against her arm, Su Yuan followed close behind Xia Linfei.
"We need to culture the cells. Each chromosome can be thought of as a double helix DNA molecule coiled and packed together. To see them more clearly, we need a large number of cells that are dividing."
Su Yuan nodded.
She understood. The blood they'd drawn contained a lot of red blood cells, but red blood cells didn't have hereditary traits or DNA. Culturing the sample would let them obtain other, more numerous types of blood cells that did have hereditary traits.
"How long will it take?"
Xia Linfei considered it for a moment. "Three days. We can use the cell growth stimulant phytohemagglutinin and culture them at 37 degrees for three days to get dividing cells suitable for observation."
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