99.99 percent
Is it possible to believe the results of a DNA paternity test
Alfiya Yenikeeva, RIA Novosti
According to various data, from five to 27 percent of women under the age of 30 cheat on a regular sexual partner. In many ways, this is the origin of the long-standing belief that from ten to 30 percent of men raise biologically not their children, without suspecting it. However, several recent works refute these ideas. RIA Novosti understands how accurate the DNA paternity test is and whether mistakes are possible during its conduct.
When the secret becomes clear
In 2005, scientists from Liverpool John Moores University, after studying data on DNA paternity tests performed in the UK, stated that about one in 25 citizens of the United Kingdom is raising someone else's child and does not know about it. This is especially often observed in partners who have not formalized a relationship officially.
Eleven years later, Belgian geneticists, who have access to huge amounts of data on genetic kinship from around the world, refuted the conclusions of their British colleagues. The Belgians referred to the fact that in the work of the staff of the University of Liverpool and the like, the results of tests from private laboratories were mainly analyzed, where they turn only in cases when paternity is in question. This means that the statistical sample cannot be considered random. The data obtained in the study of modern populations show that only in one or two percent of cases a man should doubt the origin of the child.
Moreover, it was typical for our ancestors. Scientists from the Catholic University of Leuven compared variations of a specific family Y chromosome in men who could trace their relationship back several centuries into history. It turned out that in West Flanders (Belgium region) among families whose genealogy has been known for the last five hundred years, only 0.9 percent of cases of kinship, and, consequently, paternity of ancestors was not confirmed.
American geneticists also obtained similar data by examining the DNA of the Dogon – an African tribe from Mali – and comparing the results with the pedigree transmitted orally from generation to generation. Among the representatives of the tribe, the share of unconfirmed kinship was only 1.8 percent.
Honest women
Of course, in some human communities – for example, among the South American Yanomamo Indians – the proportion of children raised by non-biological fathers can reach 20 percent. But this is only where polygamy and polyandry (i.e. polyandry) are accepted, scientists emphasize.
This state of affairs is determined by cultural and biological factors. Probably, biology here is like in the animal world: when a male believes that the cubs are not from him, he simply cares less about them or ignores them altogether.
But, unlike female animals, women have a serious evidence base for the slightest doubt on the part of a partner – a DNA paternity test.
Compare and understand
"Before the introduction of molecular genetic diagnostic methods, other unconventional approaches were used to determine paternity. Firstly, for hereditary diseases. If it is diagnosed in one of the parents, for example, the alleged father, and the child suffers from the same disease, it is very likely that we can talk about a close biological relationship. But this is only in the presence of very rare genetic diseases. Another more or less justified method is the verification of paternity by blood group indicators. Although it's not very reliable. For example, if a man and a child have a third blood group, this does not guarantee paternity, because there are a lot of men with a third blood group, this is not a rare sign. But if Rh-negative parents have a Rh-positive child, the probability that the man is not the father is high. However, it is so impossible to prove paternity. The only reliable method at present is DNA analysis," Aliyasanov, MD, Professor, head of the Department of Medical Genetics at Sechenov University, tells RIA Novosti.
Although 99.9 percent of the nucleotide sequences in human DNA match, the genomes are unique. And this individual part includes a piece from the mother and father, because both transmit exactly half of their chromosomes to the child – 23 out of 46. Therefore, a person's unique genetic profile reflects kinship.
"During the paternity test, the DNA of the alleged parent and child are compared by STR markers - these are simple repeating pieces of chromosomes. Each DNA marker has several allelic variants or alleles. The combination of alleles across all the studied sites (loci) is a DNA profile. The more markers are included in the analysis, the higher the accuracy. Sixteen or twenty markers make it possible to exclude paternity by 100 percent. But the probability of paternity only tends to 100 percent – because of the possibility of the existence of a second person with a similar genotype," explains Elena Baranova, head of the educational part of the Department of Medical Genetics of the Russian Medical Academy of Postgraduate Education, geneticist, Candidate of Medical Sciences.
"In conclusion, according to the results of genetic analysis, it may be indicated "the probability of paternity is 99.99 percent." This is a lot, and according to the regulatory documents of the Ministry of Health, it is enough to recognize a man as the father of a child," Aliyasanov confirms.
Any biological substance containing cells can be used as samples for DNA analysis: buccal epithelium (smears from the oral cavity), blood, semen, nails, even earwax. But cut hair will not work – only torn, with hair follicles containing nuclear DNA.
Anyone can make a mistake
According to experts interviewed by RIA Novosti, the accuracy of DNA analysis is affected by the number of analyzed genetic loci. As a rule, 16 to 40 STR markers are compared during the study. The more sites tested, the higher the probability of establishing or refuting paternity. One hundred percent confirmation of biological kinship is not worth waiting for, but to exclude paternity, a discrepancy in three or five markers is enough.
As for the errors in DNA testing for paternity, experts do not deny: this happens. But very rarely.
"Thanks to today's equipment and reagents, the risk of error is practically reduced to zero. Unless the human factor fails," says Asanov.
"Errors in the analysis arise due to contamination of the material or human factors - for example, mixed up test tubes. But it is easy to prevent this by strict accounting and barcoding," Elena Baranova agrees with her colleague.
The geneticist adds that DNA paternity tests are quite popular in Russia.
"The demand for such tests is primarily due to availability. Genetic research in general, even the most serious medical tests, are getting cheaper literally before our eyes. And technologies are developing so fast that invasive and non-invasive prenatal tests have already entered the market. That is, paternity can be established even during pregnancy. However, such tests personally seem to me questionable from an ethical point of view. The professional community has not yet formed an unambiguous opinion on this matter," concludes Elena Baranova.
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