Tatiana Pichugina. Scientists sequenced the genome of the men buried in the tomb of the stone age Newgrange in Ireland, and found that he was born as a result of incest. Marriages between close relatives were forbidden almost always because of the threat of degeneration. However, there is a risk of accidental incest. How dangerous is it from the point of view of genetics — in the material RIA Novosti.
Power, sealed with blood
For biological and cultural reasons, the incest taboo since ancient times. Have violated the prohibition in exceptional cases for the sake of consolidating power. Probably the opening of the Irish scientists in Newgrange associated with this — with the formation of ruling elites in the prehistoric society.
Dynastic marriages between his relatives and cousins were imprisoned in Ancient Egypt, the Inca Empire, the Royal families of the Hawaiian archipelago. Once it symbolized the purity of blood.
Most 360-thousand population of Iceland are descendants of several groups of Vikings who settled on the island in the IX century. Population is genetically very homogeneous. A few years ago a local company deCode Genetics has even released an application based on the database the DNA tests that young people are not accidentally entered into the marriage with a close relative.
DNA to the rescue
Developed computer program that compares a set of defined fragments of the genome and determining the degree of kinship. Genealogical research in General are very popular now. People do DNA tests, upload results to public databases, such as Ancestry and Gedmach, and find relatives. Especially those who don’t know its origin: grew up in orphanages, adopted.
Sometimes these surveys are presented with unpleasant surprises. So, the American woman gave her husband a birthday DNA test. The results plunged the spouses in shock: they were cousins of the first order on the father. And the couple already had a two year old child. This woman was told a year ago in the podcast of the American edition of Slate.
Scientists once warned that sperm donation is fraught with accidental incest, and recommended to strictly limit the number of single donor conceived children. In 2011, The New York Times reported about 150 half-siblings. In 2017, the British press raised the question about countries such as Nigeria, where the legislative regulation of this area is weak. Last year in the United States were widely discussed the story of Dr. Klein that deception was impregnated by his own sperm of the clients of the fertility clinic. Nearly five dozen of his biological children have found each other through public databases of DNA testing.
How dangerous is “dynastic ties”
Children of consanguineous marriages are twice as likely to get hereditary pathology, said Madina Azova, doctor of biological Sciences, Professor, head of Department of biology and General genetics of PFUR medical Institute (participant of the 5-100 Project). They have a higher risk of rare genetic diseases (orphan) caused by recessive allele — a gene whose activity is usually suppressed.
“A recessive mutant allele, both spouses can inherit from a common ancestor. They are healthy, but they have a heterozygous genotype, that is, with a given allele. The probability that such a pair of a sick child is born with homozygous genotype is 25 percent,” explains the researcher.
In this case, genetic counseling to reduce the risk of transmission of genetic pathology of a child. Experts take into account everything: the degree of relationship, health status of family members, other related marriages in previous generations, ethnicity, as some hereditary diseases accumulate in certain ethnic groups.
“During pregnancy you can go through prenatal genetic diagnosis in order to obtain the most accurate data on the genetic material of the child”, — said the Azov.
Meanwhile, according to various estimates, about a billion people live in closed communities, where closely related marriages are not uncommon and even encouraged. For example, in Egypt, men could marry only if they had a home. Accordingly, the problem was solved by the marriage between relatives living under the same roof, as a rule, cousin.
“In southern India, more than 52 per cent of marriages between cousins and second cousins and sisters. Many peoples live like thousands of years and still has not disappeared from the face of the earth because of a rare recessive gene associated with any disease,” — says Dmitry Sosin, molecular biologist, head of the Center for biotechnology, associate Professor of internal medicine Department of the medical faculty of the INPE NRNU MEPhI.
A person is able to adapt to almost any situation, says Sosin. The most serious disease, incompatible with life, are eliminated at the stage of zygote — fusion of gametes or the first few divisions of the embryo. If the pathology is not fatal, the child may be born.
“The most famous example we have is the Royal family of Holstein-Gottorp-Romanov, in which the Tsesarevich Alexei Nikolaevich was a carrier of hemophilia gene, like many of his relatives — the descendants of Queen Victoria. Most variants of hemophilia is due to a recessive gene in the X chromosome, that is, the woman will get sick only when the carriers are both parents, which is rare,” continues the scientist.
And cites another example is Turkey, where marriages between cousins are brother and sister are quite common. The infant mortality rate there is high, and among older people, the average for countries with similar income and social security. This phenomenon is called “Turkish puzzle” or the “Turkish puzzle”.
“In 1968, 27 percent of marriages in Turkey were concluded close relatives. In 2008-m — 24. Studies have shown that, in General, closely related marriages of the first degree, that is, between the cousin brother and the sister, increase infant mortality by 45 percent. This is another insurance, by which nature removes from the equation the lives of children, can not exist physically complete”, — says Dmitry Sosin.
However display some average value of the risk of pathologies in closely related marriages is incorrect. Each case is unique. It is especially difficult with multifactorial diseases, the causes of which remain outstanding. They can be, by the way, environmental, rooted in lifestyle. For example, schizophrenia. Parents with this diagnosis, the risk of transmission of the pathology of the child — 29 percent, while if they are close relatives — 41%. According to some, children born in the marriage between the cousin brother and the sister, slightly worse IQ (0.8-1.3 points).
On the Internet write that in closely related marriages, almost half of the children with hereditary pathologies. In fact, stresses Sosin, much less. According to various estimates, from one to nine percent, if we are talking about parents who have each other cousin and sister in the first generation.