Recently, a post on the Tianya Forum has attracted the attention of netizens: through the national DNA comparison, the Nanchong public security department successfully recovered the missing child for six months. Witnessed by the public security police and the staff of the City ’s First Social Welfare Institute, the lost child soldiers (pseudonym) returned to their parents. This is also the first missing child successfully found by DNA testing in Nanchong.

According to an investigation, Bingbing is a left-behind child. His parents worked in Shenzhen. He usually lives with his grandparents. The soldiers who returned home on time on May 15th at around 5pm did not return. Until 7 pm, the two old men went around looking for unsuccessful information and called their son to inform their grandson about the possible loss, and immediately reported the case. Bingbing ’s parents rushed back to Nanchong immediately, mobilizing all their friends and relatives to find the whereabouts of their son. The police conducted a intensive search while reporting the case to the Municipal Public Security Bureau and the Municipal Abduction Office. The turnaround occurred when the city's public security bureau was collecting DNA from children in the city's No. 1 Social Welfare Institute. By comparing with the DNA database of the Ministry of Public Security, it was discovered that a child named Bingbing and the DNA of Bingbing's father matched. For the sake of prudence, the civilian police fully verified the basic conditions of the soldiers and soldiers. Through his various characteristics and repeated collection and testing of DNA, the children ’s soldiers and soldiers in the orphanage were the missing children. So, what is the method of paternity testing in ancient times?

Biochemical analysis instruments help DNA detection

The original paternity test method lacks scientific basis

Appearance comparison

Due to genetic reasons, the appearance and skin color of father, son, mother, siblings, etc. generally have some similarities. It may be the most primitive method to determine the parent-child relationship by comparing the appearance and appearance, but this method is just a guess. , Judgment, as a reference.

Bone test

Bone drop test is to drop the blood of the living on the bones of the dead. If the blood can penetrate into the bone, it is determined that the living and the dead have a blood relationship, otherwise there will be no. "The Biography of Kuaiji Xianxian" written by Wu Guoren Xie Cheng in the Three Kingdoms period records the case of claiming the elder brother's bones on top of the bones of the brothers; An example of a relative test on the father's bones; in the Song Dynasty, the famous forensic scientist Song Ci included the bone-dropping method in the "Injustice Collection". From a modern point of view, this method is not scientific but creates a pioneer It is the first to use blood type to identify the relationship between blood sources.

Blood test

The blood drop blood test is also called the blood test, which is to put the blood of the child and the blood of the adult together. If it can be melted together, it is the parents' birth, otherwise it is not the birth. This method of identifying samples has been recorded in forensic works in the Song Dynasty in China. This method has no scientific basis. The blood of the parent-child relationship may not be fused, and the blood of the non-parent relationship may be fused.

Centrifuges, amplification instruments and other analytical instruments assist in paternity testing

With the development of science and technology and the change of traditional family concept, the level and demand of modern biotechnology coincide.

Paternity testing is the use of medical, biological, and genetic theories and techniques to analyze genetic characteristics from similar characteristics in the morphological structure or physiological functions of offspring and parents, to determine whether the parent-child relationship is biological.

The first step: how is the paternity test for 1-3 ml of venous blood drawn? First, collect the blood sample and start extracting the DNA inside. Blood sample collection is the same as blood drawing, as long as 1-3 ml of blood is drawn from the human venous blood vessels. The experimenter placed the collected blood in a 1.5-ml centrifuge tube containing anticoagulant. Next, the experimenter took a little blood and added DNA extraction solution to it. The reason why the extraction solution is added is to extract the DNA from the cells and remove other substances, so that the detection can be better. The experimenter put the sample into a centrifuge and began to centrifuge, the purpose is to completely separate the protein red blood cells and DNA in the sample. After the centrifugation is completed, the liquid in the centrifuge tube can be clearly divided into two layers, and the bottom layer looks slightly dark red. This is the protein red blood cell. "The top layer of clear and transparent liquid is DNA, and it can be separated separately in the next step." The experimenter poured cold ethanol into the transparent liquid, and then turned the tube upside down, and soon a white cotton wool appeared inside. s things. "This white cotton wool is DNA."

Step 2: Comparable after 2-3 hours. Although some DNA was extracted in the first step, it could not reach the amount required for our experiment, and it had to be amplified. "In order to meet the detection requirements, put a small test tube into an instrument called an amplifier. After putting the test tube into the amplifier, the DNA extract inside will continue to multiply. Under normal circumstances, after 2-3 After hours of amplification, the amount of DNA extract can reach the detection amount. After reaching a certain detection amount, DNA detection and comparison can be performed. The experimenter puts the small amount of DNA that has just been extracted into a new test tube, and then adds the parent-child Identification reagents. After adding these things and mixing with DNA, the experimenter puts the small test tube into the amplification instrument for amplification.

Step 3: All 16 sites are aligned. After the biological DNA is amplified, the site alignment starts. "Li Xiaofeng said that this process requires putting the DNA into a completely enclosed instrument and fixing it in a position, and then the device will automatically extract the DNA extract from the test tube. Under normal circumstances, the device will automatically extract 16 bits Then, the system automatically compares the two samples that need to be paternity tested. According to the principles of genetics, if all the site genetic information can be successfully matched, it can be roughly said that the father-son or mother-child relationship is paternity Because everyone has two chromosomes, one is given by the father and the other is given by the mother. Two identical values ​​will also appear at the same site, one from the mother and the other from the father. If This is true for the 16 sites. Basically, it can be said that it belongs to a biological relationship. If the child has a value and the parent does not, then they are most likely not a parent-child relationship.

DNA inspection is widely used to assist in the detection of cases

In recent years, the progress of human genome research has changed rapidly, and molecular biology technology has also been constantly improved. With the continuous penetration of genomic research into various disciplines, the progress of these disciplines has reached an unprecedented height. As the most cutting-edge criminal biotechnology, DNA analysis provides a scientific, reliable and fast means for forensic physical evidence inspection, which makes the physical evidence identification transition from individual exclusion to a level where the same determination can be made. Accurate and reliable evidence is provided for the detection of major and difficult cases such as rape and homicide cases, corpse-breaking cases, and cases of rape and pregnancy. With the development and application of DNA technology, the detection of DNA marker system will become an important means and way to solve the case. This method is very mature as a paternity test and is also the best method recognized internationally.

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