DNA paternity testing is now a very routine forensic technique. When it comes to "DNA", everyone immediately automatically makes up words such as "precision" and "high technology".
However, more than a decade ago, a strange case occurred in the United States, but while lamenting the wonders of nature, we also had to think: What kind of attitude should we have in the face of science?
Who the hell is this kid?
In 2002, 26-year-old Lydia Fairchild broke up with her boyfriend Jamie Townsend.
She raised two children with her ex-boyfriend alone and was pregnant with a third child in her belly.
Lydia and her children
As a single mother, Lydia's life is difficult, and unemployment has made her life worse, so she is ready to apply for government relief.
In the process of applying for relief, Lydia was asked to provide proof of blood ties to the child. However, the results of the DNA paternity test showed that Lydia was not the biological mother of her two children!
Law enforcement agencies suspected that Lydia was involved in human trafficking or illegal surrogacy, and immediately launched an investigation into her.
Lydia fell into a panic.
She began frantically searching for evidence that she was the biological mother of two children: a picture of her pregnancy, a birth certificate of her child. She called her parents and obstetrician for help, and both the mother and obstetrician testified in court that Lydia was the biological mother of her child.
But none of this worked!
DNA testing is considered the gold standard for blood relationship testing, and the test results are there, irrefutable.
To rule out the possibility of human error, the court asked several other laboratories to re-test the DNA samples. However, all the test results were the same: the child was not born to Lydia!
Even more mysteriously, through DNA kinship testing, law enforcement officers found that Jamie was the biological father of the two children, and Lydia's mother, the child's grandmother, was related to the two children.
The judge who presided over the bizarre case was also very confused, but he decided not to jump to conclusions. Because Lydia was pregnant with her third child at the time, the judge ordered that when Lydia gave birth to her third child, a special person was sent to monitor the scene and then do a paternity test.
Originally, everyone thought that with the birth of the third child, all the mysteries would be solved, but the mystery was even more difficult to solve.
Because, the results of the paternity test on the third child are the same as the previous results: the third child is not "born" by Lydia!
Why wasn't the child Lydia had her "biological" child?
Lydia's lawyer Alan? Alan Tindell decided to investigate the case to the end.
While investigating the case, Mr. Tyndall stumbled upon a report in the New England Journal of Medicine and took inspiration from a patient named Karen.
There was another person living in her body
In 1998, 52-year-old Karen Keegan was at the low point of her life when she suffered from local sclerosing glomerulonephritis and kidney failure and needed a kidney transplant.
In order to compare the matches between her and her two sons, doctors at the Beth Israel Deaconess Medical Center in Boston gave them a DNA test, but the test results were unexpected: Karen's two sons did not match her DNA!
Karen recalled that at that time, the doctor asked her many questions, such as which hospital her child was born in, whether it was IVF, and even asked her if she was not telling the truth, whether she had a mental disorder.
Whether it's for the purpose of healing people or a strong curiosity about academic issues, doctors in Boston want to find out.
They then took samples of cells from all over Karen's body, including blood, hair, and oral epithelial cells. However, test results showed that Karen was not her son's biological mother.
At this moment, Karen suddenly remembered that she had had a thyroidectomy some time ago, and maybe this thyroid slice could come in handy.
After some twists and turns, the doctor found the thyroid gland that Karen had previously removed. Using DNA from thyroid cells, the doctor found that this time it was right: Karen's thyroid cell DNA and her son's DNA were combined!
At this point, the mystery is finally solved: it turns out that Karen is a chimera. Or rather, Karen was her own twin sister.
The doctor in Boston explained, "It's like, in her blood, Karen is one person, but in some of her other organizations, she's another person." It was as if two people had come together. ”
What is a chimera
Chimeras have two different sets of cells, two different sets of DNA.
The cases discussed above are all in an extremely rare case in which two fertilized eggs are grouped together during conception and develop into a fetus, thus forming a chimera.
Which parts of the chimera's human body have the same (or different) DNA depends on which germ layer the cells from the two fertilized eggs eventually enter.
During embryonic development, hair develops from the ectoderm, blood develops from the mesoderm, and the thyroid gland develops from the endoderm.
In Karen's case, her thyroid DNA is different from hair and blood DNA, indicating that during her fetal period, cells derived from one fertilized egg entered the ectoderm and mesoderm, while cells from another fertilized egg entered the endoderm.
Scientists in the lab sometimes artificially create chimeras to study scientific problems. For example, in the process of making transgenic mice, scientists beat the modified mouse stem cells (transgenics) to the blastocyst stage fertilized eggs, and especially use stem cells and fertilized eggs with different coat color gene backgrounds, by observing whether the mice born are hair hue, scientists know whether the mouse is a chimera containing transgenics. The chimera mated further to obtain transgenic mice [5].
For example, scientists sometimes inject human induced stem cells into developing mouse embryos into adult human-mouse chimeras for studying human embryonic development processes and certain diseases. Of course, this kind of research is also full of controversy.
It is important to note that chimeras and hybrids are often confused, but they are two different cases. Mules, for example, are hybrid animals— the offspring of horses and donkeys, and are used for human production by combining the best traits of both. Every cell in the mule's body (except mammalian germ cells and lymphocytes)[9] has the same genetic information.
Chimeras are different, which are a mixture of different cells.
In the movie "Finding the Dragon", Ying Caihong, the leader of the number one villain cult played by Liu Xiaoqing, is looking for flowers on the other side to prolong his life because he has brain cancer. At the end of the film, Ying Rainbow tries to catch the "other side of the flower" but is buried in the sea of fire, and in the close-up of her face, it can be clearly seen that her two eyeballs are different colors: one black and one blue. This is actually a kind of chimerism. This particular physiological trait was boasted by Ying Rainbow that he had the heavenly eye to see the past and the future, and used it to seduce the congregation.
California-based model and singer Taylor? Taylor Muhl is also a documented chimera case.
Compared with Karen, her chimeric signs are more obvious, the sides of the central axis of the abdomen are clearly distinguished, the difference in skin color is visible to the naked eye, and at first glance it is a huge birthmark.
Taylor Muhl
Taylor has two sets of immune systems and sees each other as aliens, so she has autoimmune disease problems and suffers from allergic reactions.
A more extreme example of chimeric signs is that cells from two fertilized eggs are involved in reproductive system development, and the two fertilized eggs happen to be of different sexes, forming so-called "true gender deformities" that need to be surgically corrected in early childhood.
Chimeras may occur after a bone marrow transplant
Bone marrow is the hematopoietic tissue in our bones that is responsible for making white blood cells, red blood cells, and platelets. In a bone marrow transplant, doctors use chemotherapy or radiation therapy to destroy the diseased bone marrow of all recipients, and then place the donor's healthy bone marrow in this position.
According to a report in the journal Scientific American, the donor's bone marrow will continue to make blood cells with donor DNA, and then the recipient will become a chimera.
A paper published in the journal Nature states that in a "complete chimera," all of the recipient's blood cells contain the donor's DNA, but there are two copies of DNA from the donor and the recipient in the blood, which is called "mixed chimerism."
Motherboard reports that in popular culture, this type of chimera inspires an interesting storyline. The 2015 film "Bad Blood" is about a serial killer of a cancer patient who uses DNA in his blood to allude to his bone marrow donor.
Doctors say that, scientifically speaking, one person is replaced by another.
DNA testing and paternity testing
DNA testing for forensic identification benefits from the British Aggreko? Innovation and promotion by Sir Alec Jeffreys.
In simple terms, DNA testing takes advantage of the difference between people in "variable number tandem repeats" (VNTR). As the name suggests, VNTR is a DNA sequence that consists of repeating sequences, and the number of duplicate copies varies from person to person.
The length of VNTR varies greatly from person to person, but between people who are related by blood, the sequence is genetically similar.
Comparing the VNTR sequences of mother (M) and child (Ch) and three men, it can be judged that male No. 1 is the biological father
Individual differences in VNTR, as if each person had a unique set of DNA fingerprints in their own genome, can be used as evidence of identity confirmation in criminal cases and often as a means of paternity testing.
However, even if it is as powerful as DNA testing, in the face of magical nature, there are times when it is lost. Lydia's paternity testing confusion is a case in point.
Science is constantly improving. Now we watch the blood test in the costume drama feels that it is not reliable, after dozens of hundreds of years have passed, people in the future will not feel low to explode when they look at our current DNA testing?
Editor: Shen Xiangsha