Chapter 44 Chapter 44: Chromosomes
“Of course chromosomes can be checked!” Xia Linfei looked at Su Yuan curiously. “Why are you suddenly interested?”
“Nothing special, just curious.”
In truth, Su Yuan wanted to know whether her chromosomes were XX or XY. If XY, then her current female appearance might be a false state, something science could not yet explain. If XX, at least her body and appearance matched, even if that meant losing hope of returning to her male form. At least she would have clarity and direction.
So when she heard chromosomes could be examined, she felt a surge of impulse.
“The human body has twenty‑three pairs of chromosomes: forty‑four autosomes and two sex chromosomes. Male sex chromosomes are XY, female are XX. During reproduction, men produce sperm carrying either X or Y, while women produce only X eggs.”
“I know. Men provide X or Y, women provide X. Fertilization with XX yields a girl, XY a boy. So the sex of the child depends entirely on the father, since only men carry Y.”
Xia Linfei smiled. “Good thing you study biology. Easy for you to understand.”
“Since you’re curious, I’m working on human gene polymorphism. Want to provide a sample for my project?”
“My sample?” Su Yuan hesitated.
Her transformation was bizarre. She suspected her genes. The human genome has about three billion base pairs and nearly 100,000 genes, though only about 25,000 have been identified. Who knew if her DNA carried a mutation causing sex change. If exposed, it could bring trouble.
“Reluctant?” Xia raised her brow. “We’ve already collected over ten thousand samples. One more won’t matter.”
Still uneasy, Su Yuan asked, “What exactly is gene polymorphism?”
“Simply put, genes controlling traits aren’t identical. DNA must transmit accurately but also allow variation. Different groups adapt to environments, so genes for the same trait can differ.”
“For example, genes for single eyelids may vary even if they all express the same trait.”
Su Yuan nodded. “So the useful information is the same, but non‑coding regions mutate, making them different.”
“Exactly.” Xia gave her a proud look. “Variations can be single base deletions, changes in repeat sequences, or scattered insertions and substitutions. Our project studies these distribution patterns.”
“So you select specific genes for comparison?”
“Yes. We chose genes for eyelid type, hair color, and earlobes.”
“I thought you checked all genes.” Su Yuan sighed in relief.
Xia patted her shoulder. “Checking all genes is the Human Genome Project. That took years and multiple countries. Even with three genes, we split into groups and the workload is huge.”
“I didn’t know.” Su Yuan laughed at herself. She had worried about unknown genes being exposed, but the study was limited.
“Since you’re curious about chromosomes, if you provide a sample, I can show you your own.”
“Wouldn’t that be troublesome?”
“Not at all. Just a small task.”
Su Yuan agreed.
Xia brought a lab chair, fetched a disposable needle and two blood tubes.
Seeing them, Su Yuan stammered, “You… you need blood?”
“How else do we get DNA. Roll up your sleeve.”
“I thought cheek cells would work.” Su Yuan muttered, but obeyed.
She wore a light purple long‑sleeved shirt despite the heat.
“We need peripheral blood.”
Her pale skin showed as she rolled up her sleeve. Xia admired it. “Your skin is so fair.”
Su Yuan chuckled nervously. “Go ahead.”
She tied the band, tapped the vein, and inserted the needle.
“Wait! Are you skilled enough to do this in one try?”
Xia frowned. “I studied medicine. This is easy. Your veins are clear. One try is enough.”
“Oh.” Su Yuan felt the sting, watched red blood fill the tubes.
“Done.”
“What next?” Su Yuan pressed the cotton ball.
“We’ll culture the cells. Chromosomes are DNA spirals condensed together. To see them clearly, we need dividing cells.”
Su Yuan nodded. Red blood cells lack DNA, but culturing would yield dividing cells with genetic material.
“How long will it take?”
“Three days. With phytohemagglutinin at 37°C, we’ll have cells ready for observation.”
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