In 1958, Soviet biologist Ilya Darevsky described a genus of lizards that consisted only of females. This was a major world discovery. Before that, it was clear that such a phenomenon as parthenogenesis ("virgin reproduction" in which female reproductive cells develop in an adult organism without fertilization) exists. This process has been described in insects. But no one imagined that female vertebrates could also do without males.
Oddly enough, parthenogenesis is recognized by biologists as sexual reproduction, since the offspring develops from the germ cell. So why, next to the genus of lizards, which reproduce in the usual way for vertebrates - through the fusion of male and female chromosomes, there is a genus that consists only of self-reproducing "women"?
The head of the laboratory of genome organization at the Institute of Gene Biology of the Russian Academy of Sciences, Doctor of Biological Sciences Alexei Ryskov explains: “Parthenogenesis is still a mysterious phenomenon for scientists, there are many fundamental questions. It was once believed that the options for meeting the “children of parthenogenesis” are very rare, they must be unviable. Then we realized that there are entire genera of female lizards and snakes that have cloned themselves for millennia. Such natural cloning suggests that at a certain stage, some kind of female with altered properties arose, which became unisexual as a result of complex transformations. Such same-sex females are descendants of individuals of bisexual species. At the moment, we know that among vertebrates, parthenogenesis is common only in reptiles - these are lizards and snakes."
The main question relates to the topic of the accumulation of mutations. If the process of degeneration, that is, the deterioration of the phenotypic characteristics of the offspring, is observed even with closely related crossing, then what about cloning oneself?
Throughout life, the body accumulates mutations, which it transmits "straight" to its offspring. It turns out that the offspring should be less viable in relation to the parent, and the line, therefore, runs the risk of quickly fading away. However, parthenogenetic lizards have been proven to exist for millennia.
Russian scientists from the Institute of Gene Biology, Russian Academy of Sciences, with the support of the Russian Science Foundation, decided to find out how parthenogenetic mothers and their daughters differ at the genome level. The task was also set to understand the devices of the genomes of same-sex females and compare them with the genomes of bisexual females. For comparison, the genomic data of the "historical parents" of the same-sex lizard were taken.
“We know of two bisexual progenitors,” explains Alexey Ryskov. “It is also clear which of them is paternal, which is maternal. As a result of hybrid crossing about 10 thousand years ago, an altered female was formed, which became unisexual. So she lives, self-worshiping. Now all three genomes have been sequenced, we are at the stage of comparing them”.
Lizard Rostombekov. Photo: public domain
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It is clear that the genomes of the "historical parents" have mutated over the millennia. Even when studying clones, scientists are already finding mutational events. Another question is how significant the mutations are and how long they persist.
The question of the emergence of the mechanism of parthenogenesis and its expediency is still open. Why, in one case of hybridization, an unviable offspring appears, and in the other - a whole genus of clones that has existed for millennia?
There are hypotheses that describe the possibility of a bisexual individual turning into a unisexual one. For example, the balance hypothesis of Moritz (S. Moritz) suggests that when crossing, the maternal and paternal species must be close enough to get a viable individual, but at the same time far away so that any strong changes in the process of cell functioning can occur. However, as soon as scientists in the laboratory are trying to achieve the emergence of the first mother who is capable of "immaculate conception", thoughts of unaccounted for details immediately arise. Perhaps these subtleties are hidden in the interaction of two genomes: nuclear and mitochondrial.
It is assumed that all these fundamental questions should be answered by a study by scientists from the Institute of Gene Biology, Russian Academy of Sciences.
Anna Urmantseva