In a rare occurrence, a murder victim had two sets of DNA

Forensic tests on the victim of a murder case have shown that he had chimerism. This means that his body contained genetically different cells, as if these cells belonged to two different people.

In this case, the unknown woman, whose identity was not established, had different proportions of male and female cells in different tissues of her body. Biologists say that the most likely explanation for this phenomenon is that this person was formed from a single egg that was simultaneously fertilized by 2 sperms; One carries the X chromosome and the other carries the Y chromosome.

David Haig, a professor at Harvard University, described this case as very remarkable but emphasized that such a phenomenon is not completely unprecedented. In some cases, outward signs of chimerism are visible; For example, a singer named Taylor Moehl has tried to raise public awareness of this condition by bringing up her chimerism status. However, in most cases, chimerism is only detected through genetic testing.

The same was the case with this murder victim. This woman lived in China and died from a gunshot wound. Examination of the blood left at the scene of the accident showed the presence of the Y chromosome, and this led to additional tests. The results of these tests showed that throughout the body of this woman, there were different ratios of female cells with XX chromosome arrangement and male cells with XY chromosome arrangement.

One of the ways to form XX/XY chimerism is the union of non-identical twins. In this case, 2 eggs are fertilized separately to form 2 embryos that would normally become non-identical twins, but instead fuse together. In the past, it was thought that an egg can be divided into 2 eggs and each of them is fertilized separately and then the resulting embryos merge with each other. The Chinese forensic team has also proposed such a scenario for this case.

But Michael Gabbett, a researcher at the Queensland University of Technology, rejects this possibility. According to Gabbett, it is more likely that an egg was fertilized by 2 sperm and as a result, a fertilized egg with 3 sets of chromosomes was formed. These sets are then multiplied and create 6 sets of chromosomes, and after that, the egg is divided into 3 cells. Among these 3 cells, 2 cells have received one set of chromosomes from the egg and one set from the sperm, and thus they have been able to grow normally. The third cell received both of its chromosomal sets from sperms and as a result suffered abnormalities that most likely caused the loss of its cell lineage.

This phenomenon is sometimes called trigametic chimerism. David Hague also agrees with this explanation and considers it the most likely scenario. This condition is so rare that only 2 pairs of half-identical twins have been identified in the world. In the case of this murder victim, the cells were not separated and all contributed in different proportions to the formation of all parts of his body. Although several other cases of trigametic chimerism are also known, according to the Chinese research team, this is the first time such extensive experiments have been performed on different organs of a person.