Super Time Detective

Friday, August 2021, 8 at 6:45am.

Ye Huairui drove the car into Jincheng University, and then drove all the way to the downstairs of the School of Health Sciences. After parking the car, he took the elevator and went straight to the sixteenth floor.

"Knock knock."

He raised his hand and knocked on the door of the genetic information engineering office.

Soon, a fat female teacher opened the door for him.

Ye Huairui smiled politely at her, and told her why she came:

"Sorry, I'm looking for Tan Xi."

"Oh, I remember you are from the police forensic examination, right! A forensic doctor?"

The female teacher was obviously impressed by Ye Huairui's pretty face, and immediately recognized his identity, "Ajun is in Room 4."

As she spoke, she pointed in the direction of the corridor:

"Go straight to the end, the one on the right hand side of the corner is there, you can go find him yourself."

Ye Huairui thanked the other party, and followed her instructions and went to the No. 4 laboratory.

The "Ajun" in the female teacher's mouth is named Tan Xi, which is the reason why Ye Huairui made a special trip to Jincheng University.

Tan Xi is a senior whom Ye Huairui met through the fellowship association when he was at the University of Pennsylvania. He is not studying forensic science, but genetics.

Tan Xi is 34 years old this year, but because of his short stature, he has a baby face, his eyes are short-sighted, and he wears a pair of thick-bottomed glasses all year round. He looks much younger than his actual age. If you don’t know him well Some people even thought that he had just graduated from university not long ago.

Tan Xi has a very good mind. During his Ph.D. study, the grades of professional courses showed up, and a row began with the letter A.

However, he is a typical science OTAKU. He is more homely and lazy than Ye Huairui. He is only obsessed with raising various slime molds, so he was nicknamed "A Fungus" by his classmates.

It may be that the idea of ​​a genius is different from that of ordinary people. Not only was Tan Xi not angry at all when he was called a nickname, but he recognized it happily.

So the nickname "Ajun" has become a nickname, which has been used to this day, from Penn University to King University, from classmates to colleagues.

When he was at the University of Pennsylvania, Ye Huairui was one of Tan Xi's few good fellow villagers.

For a while, the two even rented an apartment together, and Ye Huairui was fortunate enough to take care of the Phytophthora polycephalum in a 34°C incubator for him.

Later, the two returned to China after finishing their studies, and they both chose Jincheng to work.

However, Ye Huairui entered the Forensic Laboratory of Jincheng Judicial Police Bureau, while Tan Xi worked as a researcher in the genetic engineering laboratory of Jincheng University.

This time, forensic doctor Ye came to Tan Xi to seek expert assistance for the bone corpse they found in Fulan Village.

Ye Huairui came to the No. 4 laboratory and looked in through the glass window. At a glance, he saw a person with his back to the window. Adding a piece of chocolate in it can almost seamlessly COS the L in "Death ○".

"Dong dong."

Ye Huairui knocked vigorously on the door twice.

The monkey on the computer chair turned back half a circle, revealing a baby face wearing thick bottle-bottomed glasses, it was Tan Xi himself.

Tan Xi's lips moved, and made another gesture of twisting the doorknob.

Judging from the shape of the other's lips and movements, Ye Huairui probably meant that the door was unlocked and he came in directly.

Of course, Forensic Ye did so unceremoniously.

"How is it, how is the mitochondrial SNP typing I asked you to do?"

Ye Huairui is used to being straight to the point when doing things, and he goes straight to the point when he comes in.

As he spoke, he glanced at Tan Xi's computer screen, and sure enough, it was densely packed with cultivation records of slime mold.

"Oh, done."

Tan Xi pushed the slipped glasses on the bridge of her nose, turned back while still maintaining the posture of squatting on the computer chair, took out a stack of reports from the drawer, and put it on the desktop with a "snap".

"Let's go straight to the conclusion."

Tan Xi patted the table and said to Ye Huairui:

"The genotypes of the 60 SNP sites of the examined bones and the suspected sisters are consistent, which is in line with the law of maternal inheritance, and the relationship between the two cannot be ruled out."

Yes, what Ye Huairui asked Tan Xi to help with was not the current routine DNA test, that is, autosomal STR typing, but mitochondrial SNP typing.

Under normal circumstances, when conducting genetic relationship identification, the first choice should of course be to use nuclear DNA on autosomes for STR typing, because this test can provide the maximum amount of genetic information and is most helpful for judging the case.

However, what Ye Huairui and the others dug out was a bone corpse that had been buried in the soil for more than 30 years, and its flesh and blood had rotted away.

Not only is there no soft tissue on the body that can provide DNA testing, even the bones are no longer fresh.

When the sample material has been severely degraded, it is basically difficult to make useful results by autosomal STR and SNP analysis based on nuclear DNA.

At this time, it is the turn of mitochondrial DNA to play.

Mitochondrial DNA is the only extranuclear genome in human cells. It contains about 16569 base pairs and is a double-stranded closed circular DNA molecule.

Compared with the DNA in the nucleus, this DNA molecule has the characteristics of high mutation rate, high copy number and almost no recombination.

It is especially useful in trace, degraded or severely corrupted samples.

In short, it is much more durable than the DNA in the nucleus.

Even if the DNA in the weak nucleus has been degraded to a mess, the mitochondrial DNA can still hold on, even if it is only a small amount, it can be revived in situ through PCR amplification, and its number can be increased to a detectable level.

According to a report in the journal "Nature", German scientists have successfully extracted the mitochondrial DNA of humans 40 years ago, and reconstructed an almost complete mitochondrial genome of ancient humans through the information of mitochondrial DNA.

Even the mitochondrial DNA can be extracted from paleontological remains with a unit of 10 years or [-] years, so it is naturally no problem to bury a skeleton corpse that has been buried for more than [-] years.

However, for all the advantages of mitochondrial DNA, there are also obvious disadvantages.

The biggest one, is that it only relies on maternal inheritance.

Mitochondria are found in all cells in the human body except mature red blood cells, but only women have mitochondrial genes that are passed on to their offspring with their eggs.

Male mitochondria are not hereditary, and its gene chain can only accompany its owner through the whole life, and then there will be no more.

On autosomes, parents each provide half of the genetic genes to their children, but mitochondrial DNA can only be passed on through the maternal line.

In other words, a man's mitochondrial DNA was given to him by his own mother and has nothing to do with his father, and he will not pass on this DNA double strand to his son or daughter.

As a result, anyone who wants to use mitochondrial DNA to prove the identity of a deceased person has to go to the immediate maternal family members.

Fortunately, Situ Yingxiong, who is suspected of being a bone corpse, has a sister born to the same mother, Situ Danni.

That's why Ye Huairui told Police Officer Huang that he only wanted Situ Danni, not Wang Yan.

——Because the mitochondrial DNA on Wang Yan was inherited from her mother, it has nothing to do with Situ Yingxiong.

Of course, in the early days when forensic medicine began to carry out mitochondrial DNA testing, due to multiple factors such as its maternal inheritance characteristics and immature testing methods, the accuracy was often questioned.

When there was a trial in Midi, the defendant's lawyer questioned that the identification report of only a few mitochondrial DNA fragments was not trustworthy at all-"At this low resolution, there may be thousands of people with Same mitochondrial DNA typing!"

Then the court really accepted the challenge of the defendant's lawyer and excluded this evidence.

But now, times are different.

Because most people's mitochondrial DNA is not the same.

When there are enough sites tested, only the relatives of the same maternal line may have the same mitochondrial DNA—among them, the mitochondrial DNA between the biological mother and the child, or between the same mother's siblings has the highest probability of being completely identical.

Entrusted by Ye Huairui this time, Tan Xi used the latest mtDNA-SNP60 fluorescence detection kit in this case.

This box perfectly fits the most popular slogan on Taobao - "I am expensive, but it works well".

The kit is based on the mtDNA evolutionary tree, combined with the genetic characteristics of the Huaguo population, and carefully selects 60 SNP sites with high polymorphism, low reversion rate and strong typing ability for detection.

The amplified fragment it requires is very small, which is very suitable for severely degraded specimens such as bone corpses that have been buried in the ground for many years.

Sure enough, Comrade Tan Xi is worthy of being an expert in the field of biological genetics, and he easily solved Ye Forensic's problem.

His test results showed that the genotyping of the 60 SNP loci of the suspected bone and the suspected sister Situ Danni were basically the same, that is to say, there is a great possibility that the two are siblings It proves that the bone corpse is the hero Situ.

"Great."

Ye Huairui breathed a sigh of relief.

Although he always believed that the bone corpse they dug up from the back mountain of Fulan Village was Situ Yingying, the robbery driver who had been missing for 39 years, but no amount of indirect evidence could compare to an intuitive and unique biological evidence.

Now that he has obtained this mitochondrial SNP typing test report, it is equivalent to obtaining an empirical evidence.

He was finally able to put together the missing piece in the jigsaw puzzle of that old case.

Ye Huairui picked up the inspection report on the table, reached out and patted Tan Xi who was lying in the chair:

"Thank you, Ajun, I owe you a meal, and I will make it up to you in a few days."

"you are welcome."

As a nerd who doesn't like to go out, Tan Xi is actually not very interested in food.

He just waved his hand at Ye Huairui, said "Come on" without end, then turned around, buried his head in the computer screen, and continued to work on his slime mold cultivation records.

Knowing the temper of this senior and friend, Ye Huairui didn't say much, took the report, left the No. 4 laboratory, and closed the door for Tan Xi intimately.