After 16 years of marriage, none of the three children were born to the man. His wife even gave birth to her fourth daughter in November last year, and she was accompanied by a man who had an improper relationship with her?
This case, which sounds "extremely harmful and insulting", was held in two consecutive courts on December 28.
The court session in the morning was mainly to hear divorce disputes, and in the afternoon it was to hear the personality rights dispute case between the man involved and the "third party". However, neither the wife nor Wu Moumou, the man with whom she was suspected of having an improper relationship, appeared in court and only submitted a defense statement, which included objections to the results of the paternity test. Previously, when the DNA paternity test report was taken out and it was said that the child was not her biological child, the woman also responded in the interview:
"Although he (referring to the husband) did DNA tests on his three daughters, the DNA tests are not 100% accurate...what?" DNA identification, who can guarantee 100% accuracy?"
In response, many netizens said: "Don't you believe the results of the DNA identification, just your words?" Some people even discovered a blind spot. Strictly speaking, the woman was right, Indeed, I have never seen a DNA paternity test result written as 100%.
So, why don’t the DNA paternity test results show 100%? Isn’t it accurate? Are there any other reliable paternity testing methods?
DNA paternity test results can only be 99.99%?
Let me start with the conclusion: Regardless of whether it is a biological relationship or not, the results of the DNA paternity test will not be directly marked as "100%". There are two main reasons for
.
First of all, due to the calculation method, the results of DNA paternity test are not 100%.
dna paternity testing technology is based on the principles of genetics and the use of modern biotechnology to extract and detect specific DNA fragments of the person being identified, and perform corresponding calculations and analysis on the results to draw identification conclusions. The principle is also easy to understand: Under normal circumstances, a person has 23 pairs (46) of chromosomes. A pair of genes at the same position on the same pair of chromosomes is called an allele, one from the father and one from the mother. If alleles of a certain DNA locus are detected, one should be the same as the mother and the other should be the same as the father, otherwise there may be problems with the parent-child relationship.
Currently, the most commonly used method for DNA paternity testing is autosomal short tandem repeat (str) analysis. str refers to the simple continuous repetition of some short DNA base sequences (1 to 6 or more bases in length) on the genome. The number of repetitions ranges from a few to dozens of times, and the different number of repetitions This leads to differences in the length of DNA bases in this region. During the test, if the child has a str numbered "fga", there are 22 and 25 repeated segments on the two chromosomes from the parents, recorded as fga-22/25, and the mother is fga-22/23 type, then , it can be determined that at least one allele of the father's gene should be fga-25.
A simpler and more straightforward understanding is that if the child has 22 and 25, and the mother has 22 and 23, then the father must have a 25.
In the actual detection process, a large amount of data calculations will be involved, which directly determines the detection results.
The first is the paternity index (pi), an index used to judge the strength of genetic evidence in paternity testing. When multiple genetic markers are used in paternity testing, the paternity index of each genetic marker is assumed to be pi1, pi2,...pin. The multiplication of the paternity indices of n genetic markers is the cumulative paternity index ( cpi).
From this, we can get that the probability of paternity (rcp), which measures the possibility of parent-child relationship, = cpi / (cpi + 1) = 1-1 / (cpi + 1), so the calculated result cannot be equal to 100% or 1 , can only approach 100% or 1 infinitely. Specifically, when the cumulative paternity index is less than 0.0001, the probability of paternity approaches 0 infinitely, supporting the hypothesis that the person being tested is not the biological father/mother of the child; when the cumulative paternity index is greater than 10,000, the probability of paternity is approximately equal to 0.9999 , supporting the hypothesis that the person being tested is the biological father/mother of the child (the same applies to women).
Secondly, it is not scientific to want to be about 100%.
DNA identification conclusions are based on the principles of genetics and statistics and are obtained through probabilistic analysis. Any errors and errors in the interpretation of probabilistic methods may cause misunderstandings of DNA evidence and inaccurate conclusions that are inconsistent with the authenticity of DNA-related factual conclusions. .In other words, whether the identification result supports paternity or not, it is a probability analysis result, and probability analysis cannot make an absolute "negative" or "excluded" conclusion.
Therefore, the correct paternity test result is generally expressed as:
The cumulative paternity index is... (less than 0.0001), the probability of paternity relationship is less than 0.01%, excluding a as the biological father of b;
The cumulative paternity index is... (greater than 10,000), the probability of paternity relationship is greater than 99.99%, supporting that a is the biological father of b. Will
DNA paternity test be inaccurate?
In this incident, the woman’s distrust of the identification results can be viewed dialectically.
Currently, DNA paternity testing is the most commonly used and accurate testing method. Zhao Junyi, a technical expert in the research and development of
genetic testing products, mentioned in an interview with China Women’s News, “Compared with 20 years ago, the accuracy rate is improving. The negative accuracy rate of DNA paternity testing technology is nearly 100%, and the positive accuracy rate is 99.99%. ”
Even if an error occurs, the problem is more likely to occur before authentication. After all, from the discovery of samples, the extraction of test materials, to the implementation of DNA identification, to the presentation of evidence and certification in court, every step requires human participation, and errors may occur due to subjective intention or negligence.
You should know that if the DNA sample being tested is not complete enough or of low quality, it may directly lead to inaccurate test results. For example, the hair sampled for DNA paternity testing must be plucked out by the roots and connected to the hair follicles, rather than cut off, otherwise DNA cannot be extracted.
Furthermore, the possibility of DNA paternity test errors is extremely low, but it exists.
The limitations in the principle of identification technology, the influence of external environmental factors, errors in the application of identification technology, etc. may cause errors in DNA paternity testing.
For example, genetic variation in DNA biological samples (including physiological and pathological variations such as gene silencing, gene deletion, gene exchange, gene mutation, weak antigen, chimeric antigen, etc.) may lead to the wrong conclusion of paternity; DNA biological testing materials There is a certain degree of degradation due to various environmental or physical and chemical factors, which will lead to a large number of allele deletions, thus affecting the effective application of DNA typing technology; molecular experiments due to various reasons lead to low accuracy and unclear maps, and produce misjudgments.
In addition, according to the number of participants, paternity testing can be divided into triple paternity testing in which both parents and children participate, and single-parent paternity testing in which father and son or mother and son participate. The latter may occur during the testing process due to the lack of genetic information of one parent. The str locus mutation phenomenon affects the accuracy of paternity test results to a certain extent.
A 2023 study by Huazhong University of Science and Technology found that due to the lack of genetic information from one parent, the accuracy of the single-parent paternity test will be significantly lower than that of the triplet paternity test, so its identification conclusion can only be described as excluding paternity or not excluding paternity. Parent-child relationship.
More seriously, it will increase the risk of unrelated individuals being mistakenly identified as the biological father or mother. A simple understanding is that if a child's full (half) siblings, grandparents, parents, uncles, aunts, uncles, aunts and other close relatives are identified, they will most likely be judged as the father/mother if a single parentage test is performed.
However, in response to these situations, the identification laboratory will have different people working in different batches to review each result to further reduce the probability of errors.
According to the identification results posted online, in this case, the husband did a single-parent test of 20 str loci. The results showed that "at the di9s433... locus... (the father) obviously cannot provide... (the child) The necessary allele does not comply with Mendelian laws of inheritance." This result does not support that the man is the biological father of the child.
How accurate are other paternity testing methods?
In addition to DNA paternity testing, there are many methods to detect paternity, but none of them are as efficient and accurate as them.
For example, blood type paternity testing can confirm the parent-child relationship by comparing blood types. Mendel's law of inheritance states that human blood type will be passed on to the next generation, and there is an important connection between the blood type of children and the blood type of their parents.The specific rules of each blood type system are different. Taking the Abo blood type system as an example, if a person with type A blood and type A blood are together, the child born can only be type A or type O, and it is impossible to have type B or type AB; If a person with type AB blood and a person with type AB blood are together, the child they give birth to can only be type A, type B or type AB, and type O is impossible.
In theory, the more blood types that can be tested, the higher the accuracy. But there are currently billions of people in the world, and there are a lot of people with the same blood type detected. Therefore, the results of blood type identification can only be used as a basis to deny biological relationships, rather than as positive evidence.
In addition, my country used leukocyte antigen (HLA) typing in the early days, which required a large number of blood samples and was only 80% accurate. Combined with blood type paternity testing, the accuracy can be improved to a certain extent, but it is still not as good as DNA testing.
In the 1980s, chromosomal polymorphism identification technology also appeared. Chromosomal polymorphisms, also known as heteromorphisms, refer to minor variations in various chromosome shapes that are common in normal people, such as increased somatic regions. This polymorphism can be inherited. However, this technology mainly requires technicians to observe and make judgments, and the accuracy is not high.
Now, single nucleotide polymorphism (SNP) identification has appeared in DNA paternity testing. The frequency of SNP mutations is low, and even if the sample is degraded, it will not have much impact on the results; there are more SNP sites, and about 700,000 SNP sites can be detected, with higher accuracy.
Taken together, DNA paternity testing is currently the most commonly used and most accurate identification method.
Reference:
[1] Tong Jianhua, Lou Jiatao and Liu Xiangfan: "Ten Thousand Whys in Clinical Testing: Molecular Biology Testing Volume"
[2] National Standard "GB/t 37223-2018 Technical Specifications for Paternity Testing"
[ 3] Chen Maomin, Zhou Fenglei, Huang Daixin, et al. Risks and responses to single parent identification [j]. Chinese Journal of Forensic Medicine, 2023, 38(02): 148-154.
[4] Wu Jie, Yang Jinlong, Xiong Xin et al. Erlian Risk analysis of paternity testing[j]. Chinese Journal of Forensic Medicine, 2017, 32(03):269-271.
[5] Yang Fei, Dong Lubin. Research on the impact of str locus mutations on the accuracy of paternity testing[j]. Legal Expo, 2021(19):115-116.
[6] People's Daily Online: A scientific and technological topic raised by an erroneous paternity test - Is the paternity test reliable?
[7]Global Science: Another new blood type has been discovered! This can save lives
[8]https://ib.bioninja.com.au/standard-level/topic-3-genetics/35-genetic-modification-and/dna-profiling.html
[9]https://openlab .citytech.cuny.edu/openstax-bio/exam-4/biotechnology-genomics/5/
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