A virgin gives birth？ Scientists discover genetic switch of parthenogenesis.

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　　When I was a child, I watched the CCTV version of The Journey to the West, and I was always amused by the experiences of the four masters and apprentices in the girl country. I even suspected that there was a mother and son river that got pregnant after drinking one mouthful. There is also a saying in the Western Bible that the Virgin Mary was pregnant by the Holy Spirit. Later, after studying biology, I slowly discovered that the story of the daughter country and the virgin Mary is not parthenogenesis in the biological world.

　　△ Who can face a pregnant Bajie and still hold back from laughing? (Source: Network)

　　The so-called parthenogenesis means that females can produce offspring without male participation. Although people can't parthenogenesis, this kind of reproduction is not uncommon in the animal kingdom. Many animals can do it, especially some lower protozoa, invertebrates and lower vertebrates. What is really rare is that those species that are used to sexual reproduction secretly practice a pair of parthenogenetic skills.

　　01

　　Strange California vultures

　　California condor is an endangered bird living in America. In the 1980s, its population was only 22. In order to protect this species, biologists have conducted a comprehensive tracking of California vultures, and even recorded in detail who did unspeakable things with whom, and registered the lineage of each California vulture.

　　However, when scientists reviewed these "lineages" through sequencing technology, they suddenly found that two California vultures numbered SB260 and SB517 were not related to any father. The only plausible explanation is that these two California vultures developed directly from eggs without sperm stimulation, which is the parthenogenesis mentioned above.

　　Unfortunately, when scientists realized that the situation was wrong, the two California vultures with "abnormal" bloodlines were already dead. SB260 was born in the zoo and died two years after it was released to nature. It is thin and difficult to blend in with wild birds. SB517 was born with a bent spine, difficult to walk, and did not have the conditions to be released. He died in the zoo when he was about eight years old.

　　△ California condor in San Diego Zoo (Source: Network)

　　In fact, there are many similar phenomena. California condor is not the only creature that has been found to have parthenogenesis "suddenly". Before and after this, scientists have also observed parthenogenesis in pythons, narrow-headed hammerhead sharks, turkeys, New Mexico whiptail lizards, Komodo dragons and other animals.

　　New Mexico whiptail lizards, in particular, do not have males in their populations. Before the egg is formed, the chromosomes in the cells of the whiptail lizard will double, so that the chromosome number of the egg is normal and the genetic diversity is guaranteed to some extent.

　　△ New Mexico whiptail lizard with mother and father (Source: Internet)

　　The Komodo monitor lizard, the largest lizard in the world, has also developed a skill of parthenogenesis. It can fertilize a gamete instead of sperm, but the offspring are all male. At the same time, the female Komodo monitor lizard does not shy away from offspring, and often "produces and sells itself" and quickly breeds a large family. However, under normal circumstances, the female Komodo monitor lizard will not do this, and only when there is no male for a long time will the sword go sideways.

　　In addition, pythons will also use parthenogenesis to quickly restore the severely damaged population. If you look at it this way, parthenogenesis seems to be the choice of some organisms to actively adapt to the environment under certain circumstances.

　　These phenomena also make people wonder whether there is a "genetic switch", just like the mother river, which can easily make animals parthenogenesis.

　　02

　　Scientists discover genetic switch of parthenogenesis.

　　On July 28th, a study published in Current Biology found the switch of parthenogenesis.

　　Scientists from Cambridge University in England and Tennessee University in the United States sequenced the genes of Drosophila melanogaster, which can only reproduce sexually and parthenogenesis, to find out which genes are open and which ones are closed in eggs of different reproductive forms, and quickly identified 44 genes that may be related to parthenogenesis.

　　Subsequently, scientists modified the corresponding genes in Drosophila melanogaster according to the information they had, and found that 11% of them obtained the ability of parthenogenesis. They will spend half their lives (about 20 days) waiting for a "boy in black", and if they can't wait, they will become parthenogenetic.

　　△ Drosophila's huge chromosome (Source: Nature)

　　In further research, scientists also found that parthenogenetic ability can be inherited. About 1% ~ 2% of the offspring of Drosophila melanogaster who have been induced to parthenogenesis still have parthenogenesis. However, they are still "not determined enough", and if they are hooked up by handsome guys, they will still turn to sexual reproduction.

　　The researchers said that more experiments will be done on fruit flies in the future to further study the mechanism behind this.

　　(A digression, Drosophila is a commonly used model organism in biological research, and the research on Drosophila has inspired five Nobel Prizes so far. )

　　△ Drosophila (Source: Nature)

　　03

　　Other interesting reproductive research

　　In the scientific community, parthenogenesis is not the most imaginative way of reproduction.

　　In 2004, Japanese researchers bred mice with two biological mothers.

　　In 2018, the Institute of Zoology of Chinese Academy of Sciences successfully bred mice with two biological fathers.

　　On May 10th this year, the British Parliament passed the "three-parent baby" technology bill, and these babies have a father and two mothers. At present, this technology is only allowed to treat some serious mitochondrial genetic diseases, so it is called the fourth generation assisted reproductive technology (see Yin Ge's article for details:).

　　△ Schematic diagram of the steps related to mitochondrial donation required by the "three-parent baby" technology (Source: The Guardian)

　　These technologies have jumped out of the "laws of nature" and have to make people feel that science is far more imaginative than science fiction.

　　04

　　Is it possible for humans to parthenogenesis?

　　Under natural circumstances, there is basically no possibility.

　　The genetic regulation used by humans to mark paternal or maternal genomes is more complicated, and at present, there are only half of chromosomes in female eggs, so males need to provide enough genetic information for these eggs (sperm will carry the other half of chromosomes).

　　In addition, sexual reproduction does not mean "backwardness", on the contrary, it is a relatively good way for organisms to continue in the long evolution process. Through further recombination, the genes from both parents brought about extensive genetic variation, which made the offspring more diverse and better adapted to natural selection, and also laid the foundation for the transmission of favorable mutations in the population. Some scientists estimate that from bacteria to higher animals and plants, the species that can have sexual reproduction account for more than 93%, and its importance is self-evident.

　　Assuming that a single egg cell can mature like a drone, many recessive genetic diseases will be fully exposed, such as phenylketonuria and spinal muscular atrophy. Even if such a "freak" breaks through many obstacles, diseases, tumors, etc. will accompany him all his life, and it is difficult to have a long life.

　　△ Bees are also common model organisms in biology (Source: Internet)

　　Today, with the progress of science and technology, more and more reproductive secrets are decoded by us. Maybe one day, the genetic switch related to parthenogenesis can also be found in humans, but at that time, will you choose to turn on this switch?

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　　reference data

　　[1] Oza A. 'Virgin birth'genetically engineered into female animals for the first time[J]. Nature, 2023.

　　[2] Sperling A L, Fabian D K, Garrison E, et al. A genetic basis for facultative parthenogenesis in Drosophila[J]. Current Biology, 2023.

　　[3] Ryder O A, Thomas S, Judson J M, et al. Facultative parthenogenesis in California condors[J]. Journal of Heredity, 2021, 112(7): 569-574.

　　[4] Li Z K, Wang L Y, Wang L B, et al. Generation of bimaternal and bipaternal mice from hypomethylated haploid ESCs with imprinting region deletions[J]. Cell Stem Cell, 2018, 23(5): 665-676. e4.

　　[5] Xie Ping. The design, operation and evolution of life system from the perspective of ecology-the integration of ecology, heredity and evolution through reproduction. Beijing: Science Press, 2013.