It will not be difficult for scientists to cross two or more living creatures, as well as individuals of different species. There are already chimeras of amphibians, rodents, primates, humans. RIA Novosti understands why researchers create biological monsters and what ethical questions arise in connection with this.
Twin embryos hug
Chimeras of ancient mythology are, as a rule, deities: half-humans, half-animals. Such is the Minotaur, which the Greeks portrayed as a man with a bull's head, or Faun - a man with goat legs. The Egyptians envisioned the god Anubis as a man with a jackal's head. Modern science is able to identify among people real, living chimeras, whose body contains cells of different individuals.
The birth of a chimera is caused by random disruptions in the earliest period of embryo development, for example, when two eggs are fertilized by two sperm and fuse into one embryo. As a result, the baby receives the cells of another person - his unborn twin. This is called tetragametic chimerism, emphasizing that four different germ cells were involved in the formation of the organism: two paternal and two maternal.
A chimera person can only be identified using a series of genetic tests that compare DNA from different tissues - blood, hair, saliva, genitals. It is no coincidence that most cases of natural chimerism among people have been recorded by forensic criminologists.
Outwardly, it is impossible to recognize chimera people, with the exception of interracial descendants, whose skin color resembles a mosaic, or true hermaphrodites - half-men-half-women. So, in the state of Texas in the United States, a child was born, half of which belonged to a mulatto girl, half to a black boy.
Sometimes chimerism is recognized when looking for the causes of infertility. It turns out that the second genitals develop inside a person. They are removed surgically, and the IVF procedure solves the problem of conceiving a child.
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Often, pregnant women exchange cells with their own fetus through the umbilical cord. Doctors call this microchimerism and believe that this condition goes away after a few years. However, genetic tests have shown that in some cases, the mother's body retains the baby's cells throughout its life.
Stem cell chimera
Successful organ transplantation is nothing more than the creation of a chimera, because a person then lives with a foreign organ and foreign DNA. Organ transplants are sometimes the only way to save lives, and they agree to it, even if the consequences are unpredictable.
To reduce the risk of organ rejection, scientists propose to grow it from the patient's own cells, only in another organism, for example, in a pig, whose metabolism is largely similar to that of a human. This means that you need to create a chimera, that is, to introduce human cells into the body of another creature.
The discovery of pluripotent stem cells has greatly simplified the technology. These cells are formed early in the development of the embryo. They can remain unformed for a long time, but they are also capable of forming any organ or tissue in an adult body. They are implanted into an animal's embryo, which is then implanted into a surrogate female, and the birth of a chimera creature is awaited. Besides the fact that the use of pluripotent cells from a human embryo causes serious ethical difficulties, their number is in principle limited. However, transplantation solves this problem by reprogramming mature adult cells back into pluripotent ones.
From left to right: rat and mouse chimera, rat, mouse. Photo: Tomoyuki Yamaguchi.
Chimera in a petri dish
In the mid-1980s, British scientists created a goat and sheep chimera. The resulting creature was covered in part by goats' hair, partly by sheep. This was followed by experiments on crossing two newts with different pigmentation, chicken and partridge, rat and mouse. In 2012, in the laboratory of geneticist Shukhrat Mitalipov from the Oregon University of Science and Health (USA), three rhesus monkeys were created, containing cells from six parents.
In 2013, scientists from Israel obtained mouse embryos with human cells. In 2017, a pig and a human were crossed. Although all these experiments were discontinued in the early stages of fetal development, they sparked a heated debate in scientific circles about the ethics of such research.
Will such a hybrid develop human traits? Will he develop a consciousness, as we do, if, for example, stem cells are introduced into an animal to grow brain tissue? Can a child be born from human germ cells produced by a chimera? All these questions remain unanswered so far. Just in case, the governments of some countries have limited and even banned experiments with chimeras - until the situation is clarified.
Roku and Hex - the world's first chimera monkeys from six mothers. Photo: OHSU Photos.
Tatiana Pichugina