Mohammad Pur Umriis a farming village located in the Indian state of Uttar Pradesh, not far from the city of Allahabad. At first glance, this place, surrounded by stone and mud walls, does not differ at all from any other. But the traveler who enters its streets will believe that he has seen the same person more than once, or perhaps that he has had a few more drinks before entering. Because Umri has become famous because she has the highest percentage of identical siblings in the world. Between hisonly 2,000 inhabitantsthey count nothing less than55 pairs of monozygotic or univitelline twins, that is, born from a single fertilized ovum; to thedizygotic twins or twins born from two eggsthey are usually calledTwins. This means that here, approximately one in ten deliveries ishuman clones, when the world rate is one in 250.
In one photo, two dark-haired middle-aged men with mustaches can only be distinguished by wearing different clothes and their hair, a bit more messy in one case. Another snapshot shows two sisters – one serious and the other smiling – dressed in the same school uniform; It seems like a trick, images of the same person that capture his change of mood. There are also identical babies and teenage girls who show their identity with saris – the traditional Hindu dress – of different colors.
Umri hides an almost science fiction movie mystery: the myth of the place of duplicate beings. Among the scientists intrigued by this rarity is the French biologist Bruno Reversade, a researcher at the Singapore Institute of Medical Biology, who incidentally bears a striking resemblance to actor John Cusack. ? People may not realize that when two identical individuals are born from a single embryo it is essentially the same cloning phenomenon that gave birth to Dolly the sheep ?, Reversade recounted by phone for VERY INTERESTING.
Dolly’s case, let’s remember, was an unprecedented achievement in genetics. British scientist Ian Wilmut’s team collected eggs from the Scottish black-headed sheep species, stripped them of their DNA and filled each of them with the genetic content of a mammary cell belonging to a specimen of the Finn Dorset breed. Of nearly 300 embryos, only one thrived. Dolly, born in 1996, was an exact clone of the donor, a sheep with a white face, even though her mother had a black face.
But in the case of human twins there is no outside intervention. “The process takes advantage of the plasticity of the early embryo. There are many people who tend to condemn cloning, but they do not take into account that nature itself is responsible for producing a pair of identical people every 50 seconds”, this expert tells us. Furthermore, the statistic does not take into account siblings reabsorbed during gestation, but exclusively births.
The phenomenon ofTwins-much more frequent, for example, than genetic diseases- is one of the majormysteries of biology. “We hardly know anything about it,” says the French embryologist, little given to fantasies and without any desire to appear in the media. Cloning is not his goal, he insists, but understanding the phenomenon can shed light on questions of great concern. Does it say a lot about the way aembryoself-regulates. It all starts with an egg fertilized by a sperm. Then, for strange reasons, said ovum breaks, a fact that generates two half embryos. Would it be logical for each of them to produce a semi-baby? However, such aberrations do not take place. Each half produces a complete being. “Which means that, after the partition, the semi-embryo knows that it has to regenerate the portion it has lost.” This excision usually occurs during the first week of pregnancy.
Bruno Reversade, who was educated at the prestigious Pasteur Institute and then graduated in embryology and genetics at the Pierre and Marie Curie University, both in Paris, is a frequent visitor to Mohammad Pur Umri. Try to understand why this village has become the largest twin factory in the world. Regardless, Reversade doesn’t like to express himself in terms of “this is the greatest thing.” We are not talking aboutGuinness Book of Records. The demographic growth of the Indian village hardly compensates for its loss of inhabitants due to emigration to the cities. It is a simple place, located in the vicinity of an air base, with no room to spread out. Is this isolated microworld the Shangri-La of twins? One possible clue is that the military installations were established 40 years ago, which coincides with the increase in twin births. But science has to find the cause, not just speculate, with the reasoning that “one thing leads to another.” Evidence is needed.
“The environment hasn’t changed in years that we know of,” Reversade explains. And he adds: “We have taken samples of the soil, of the milk of the cows that the locals consume and of various vegetables that the inhabitants grow, such as mustard. Of course, they all drink from the same groundwater, so you cannot rule out environmental agents exist, but the problem is that there is no known chemical capable of causing an outbreak of twinning. ” The chemical trigger that determines the critical moment of the embryo’s partition in two remains in the dark. For example,siamese-twins that are born united by some organ- are the result of an untimely division of the embryo itself, which can engender a tragedy.
As noted above, there are two types ofTwins: themonocigóticosand thedizygotic. The former derive from a single embryo, and therefore the couple can only be of the same sex. They share exactly the same DNA, albeit with some nuances. Are they physically accurate? The resemblance is undoubtedly striking, although the exact term must be placed in its genetic context. Normally, we receive two copies of a gene, one from the mother and one from the father. But there are exceptions. Certain regions of the genome can contain from zero to 14 copies, according to a study carried out by geneticist Carl Bruder, from the University of Alabama in Birmingham (USA). If it happens in normal people, it can also happen in pairs of identical twins, so that one of the members lacks genes that the other does. This was the case in a monozygotic couple: one suffered from leukemia due to the absence of certain genes, while the other remained healthy, as he did not develop the propensity.
Bruno Reversade’s goal is to find theultimate cause of twinningin human DNA. “My starting point was to start looking for rare cases of families where the phenomenon was repeated. It is something very controversial, since most people believe that it happens by chance.” Reversade bases his hypothesis on examples that can be found in nature, such as the nine-banded armadillos, Dasypus novemcinctus. These mammals usually always give birth to four monozygotic twins.
If we go back to human casuistry,Ageit is not the only case of unusual proliferation of identical persons. No less than 16 couples have been born into a Jordanian family over three generations. This model of family inheritance suggests that the cause is aautosomal dominant gene, that is, that it is not on a sex chromosome and whose presence would trigger the process. This would be your robot portrait: located on chromosome 4, it would not be very large or particularly complex. The region where it is found has undergone few changes throughout evolution, it is conservative. The gene would encode a protein that is present in the embryo during its first days, but turns off once cell differentiation has begun.
If the Reversade conjecture is confirmed, what could be the reasons for the conservation of this DNA segment in the human species? Although we are not nine-banded armadillos, a monozygotic pair for every 250 births is not a negligible figure either. Within mammals, humans score high for twin production. “I do not think it implies any advantage. For a woman, it does not make sense to give birth, since the probability of death for her and the children during childbirth is higher,” explains the expert.
There is another fact that remains a mystery: congenital defects and anomalies are two to three times more likely to occur in monozygotic twins. Why hasn’t evolution opted exclusively for the dizygotic? This is what happens with cats and dogs, which usually have twins in a single litter. If an identical twin is born with a weak immune system, his partner is also at risk. According to Reversade, a mutation in the suspected gene would be to blame for the embryo splitting in two before starting to differentiate. The cause would be a deficit of cohesive glue between your cells.
In this sense, twins would be seen as agenetic system abnormality. However, they offer an unparalleled opportunity to delve into the keys to human behavior, as well as to more clearly define the boundary betweeninheritanceand theenvironment. A classic study published in the journalScience in 1990 he laid the groundwork for the profound influence of genetics on human behavior. Its author, University of Minnesota psychologist Thomas J. Bouchard, carefully analyzed the personalities of 56 identical sibling pairs who were separated in early childhood. The question posed was an exciting one: to what extent were literary and musical tastes, fears, tics and manias, verbal skills or intelligence determined by DNA? How did education influence a different environment or family? Perhaps the most famous case is that of twins Jim – Jim Lewis and Jim Springer – separated when they barely had four weeks to be raised by adoptive families. The brothers were reunited 39 years later, but the amazing thing is that they were both exactly 1.82 meters tall and 80.6 kilos. Some anecdotes about their customs defy common sense. When they were teenagers, they had a dog that they gave the same name: Toy. They both worked part-time as sheriffs for the police, biting their nails, suffered frequent headaches, smoked the same brand of cigarettes and drank the same type of beer. And as if that weren’t enough, each one was married twice; the first women were named Linda, and the second, Betty. The Jims used to leave love notes for them. Nobody in their right mind would postulate the existence of a gene that predisposes to drink a certain brand of beer, but Bouchard’s study – to which more data is still being added today – concluded that IQ had a strong hereditary component. “70% of the observed variation can be attributed to genetic variation,” wrote the American psychologist in Science.According to this expert, the similarity of character traits could be explained because, having identical genomes, twins are more likely to select a similar environment when making decisions.
It is also true that monozygotic siblings can develop different personalities. “They have thesame DNA, butepigenome varies“Reversade clarifies. That term refers to the different form of expression of genes, even if they are identical.” People often confuse things: twins acquire varied experiences, they are not always in the same place and at the same time. . They arehuman clonesbut not monsters. And they, of course, do not consider themselves half people. They can impersonate each other, but just to joke. “
What Bruno Reversade cannot hide is his astonishment at the similarities that studies on monozygotes show with respect to the way of thinking or, as has already been pointed out, to the IQ, regardless of the environment in which they grew up. These investigations provide a wonderful tool to see how far the influence of genes extends. “They show the importance they have in many aspects of life, such as intelligence or physical appearance.” But neither should the power of external circumstances be underestimated. “I know two twins with different sexual preferences: one is homosexual, and the other, heterosexual,” the French biologist gives as an example.
Luis Miguel Ariza
