The test failed, and Mitchell was very disappointed. He took his wife to travel to Ethiopia in Africa. A local friend Aiken received him.
After hearing about Mitchell’s experience, Aikenle broke down: “I wondered why! There is such a chicken on my farm. The color of its back is divided into two. I was still wondering. Well, it seems that this guy is also a double-sided androgynous chicken.”
Mitchell’s lost confidence was ignited again. He ignored the hard work of the journey and Aiken went straight to his farm, and soon saw this strange one. As for the chicken, the feathers on its left side are red and bright, showing the characteristics of a rooster, while the pattern on the right side is the pattern of an ordinary hen. What makes him even more excited is that this chicken exercises the right of a rooster and mates with the hen. , Also fulfills the duty of the hen, laying an egg every other day.
“Can this egg hatch into a chick?” Mitchell first inspected the chicken and found that its ovaries were developing normally, and then inspected the egg and found that it was a fertilized egg, as long as the temperature was right. The chicks should be able to hatch.
After returning to the studio, Mitchell put the eggs and other eggs into the hatching room. 28 days later, Mitchell was very excited when he saw the chick coming out of the eggshell.
This successful experiment led Mitchell to the conclusion that for bidirectional hermaphrodite animals, the two sets of reproductive organs in the body cannot develop equally, especially the female reproductive organs and ovaries are more difficult to develop normally.
In order to confirm this conjecture, Mitchell used hermaphrodite lobsters and butterflies to do the same experiment six months later. After many attempts, no larvae were born. After inspection, the female reproductive organs in their bodies are all underdeveloped.
Mitchell contacted Dysons, a reproductive expert. Dysons said that unlike male reproductive organs, the development of female reproductive organs is much more complicated. In particular, in recent years, women have more infertility than men. .
After deciphering the reason why it is difficult for a bilateral hermaphrodite to produce offspring, Mitchell began to wonder about the condition of the hatched chick. Will it be hermaphrodite like its mother? Soon, the test result of the chick came out. It does not have two sets of reproductive organs in its body. It is a normal hen.
Explore the reasons
In March 2020, Mitchell published the results of the study in the journal Nature. While readers were surprised by the legend of nature, German zoologist Kirk questioned the reason why these animals are half male and half female. The body is due to accidental loss of sex chromosomes. “During the development of a fertilized egg, sometimes the cell accidentally loses a sex chromosome, which has a great impact on the final result. In a chicken embryo with a ZW sex chromosome (hen), a cell loses a W chromosome, then this cell Because of the lack of W, male characteristics will appear. If this cell starts to replicate, the cells it produces will also appear male characteristics. But at the same time, because the other cells in the embryo are still female, the chicken will eventually become hermaphrodite. But why are the two-sided hermaphrodite chickens have a perfect half-half folio?”
In fact, Mitchell has also questioned this phenomenon, and chromosome loss alone does not explain this problem.
In order to unravel the confusion, Mitchell tested the genes of a bilateral hermaphrodite chicken. The results of the examination surprised Mitchell. The chromosomes were not lost. What is more bizarre is that the chicken has a rooster and a female on both sides. Two distinct sets of chromosomes in chickens.
In other words, this chicken is actually made up of a pair of fraternal twin chickens that fuse in the center of the body.
“Why does this happen?” Mitchell remembered a case reported in the news a year ago. A husband suspected that the child was not his own, so he went to the appraisal center for testing. The final check result was shocking. The child was him. , But it has nothing to do with his mother.
Finally, after a series of tests, it was found that the child’s mother was a mosaic, that is, at the stage of conception, the mother’s genes were embedded in the sister’s chromosomes, and finally the chromosomes were concentrated in the reproductive system, so the child’s DNA showed the characteristics of the mother and sister.
Mitchell came up with a bold idea: These two-sided hermaphrodites are also a chimera, but the chimerism is just average, resulting in half male and half female.
Mitchell’s conjecture was confirmed. In further testing, he found that these animals are related to polar bodies: in the two meiotic divisions of female germ cells, a large egg cell and two or three small cells are formed. , This small cell is called “polar body.” The polar body has half of the chromosomes, but because of the lack of cytoplasm and lack of nutrients, they will quickly disappear. But sometimes, the polar body will also be retained. If both the egg cell and the polar body are fertilized, and then the cell divides, each side of the body has its own genome and its own gender. The appearance of bilateral hermaphrodite is caused by accidental fertilization of the polar body. It is a type of chimera, that is, two fertilized eggs merge into one individual to grow.
Mitchell’s test further explains why there is no bilateral hermaphrodite in humans, because the sex hormones in the blood of mammals are the key to determining the sex of the fetus. Regardless of the cell’s DNA performance, they are all affected by the same hormones, and finally develop. Show the same gender characteristics.
This is not the case with birds and other animals. The right brain (male) of half-male and half-female zebra finches has a neural circuit dedicated to singing courtship songs, while the left brain (female) does not, although the entire brain is In the same hormonal environment.
In July 2010, Mitchell published the research results in the journal Nature. Netizens commented on this: “Nature is really amazing. Although the body is composed of two halves, it can live smoothly. Each weird half of the animal is a unique accident of nature.”
Environment is the main culprit leading to hermaphroditism
A report based on more than 250 scientific studies around the world has determined the effects of chemicals on species ranging from polar bears to the oryx in the southern plains of Africa, from deep-sea whales to high-altitude falcons and eagles.
The scientists concluded that: “Each male animal in several major categories of vertebrates (including bony fish, amphibians, reptiles, birds, and mammals) is affected by environmental chemicals. Many vertebrate males Feminization has been quite common. All vertebrates have similar hormone receptors that exist in evolution. Therefore, observations of one organism may cause concern about the pollution of other vertebrates, including humans.” The
study pointed out Fish are particularly affected by pollution because they live in contaminated water. Not only food is contaminated, but their gills and skin are also contaminated. The fish was one of the first animals to show universal gender distortion. Some studies have found that half of the male fishes in the lowlands of the UK can lay eggs.
In some areas, all male cockroaches have been found to switch gender roles in this way. It is believed to have a certain relationship with estrogen. These estrogen mainly come from contraceptives and enter the water circulation system through the sewer. More than three-quarters of sewage treatment plants have been found to also discharge artificial compounds that break down androgens. Many freshwater fish in Japan and Benin Bay in Africa have male feminization. In addition, many marine fish in the North Sea, the Mediterranean Sea, Osaka, Japan, and the Puget Sound on the west coast of the United States also have male feminization.