Human chimera

Human chimera refers to a single organism that is composed of cells with more than one distinct genotype. In humans, this condition can arise through several mechanisms, including the fusion of multiple fertilized eggs in the early stages of development, the acquisition of cells from a twin during gestation, or through the infusion or transplantation of foreign cells into the body for medical treatment. This phenomenon is named after the Chimera of Greek mythology, a creature composed of parts from different animals.

Causes and Types

Human chimerism can occur through several distinct processes:

• Tetragametic Chimerism: This occurs when two separate eggs are fertilized by two sperm, and the resulting zygotes then fuse, forming a single organism with two sets of DNA.
• Microchimerism: This involves the presence of a small number of cells that genetically differ from the host's main cell population. It can occur naturally, often as a result of fetal cell transfer between mother and fetus during pregnancy, or through blood transfusion.
• Artificial Chimerism: This can be induced through medical procedures such as organ transplantation, where the recipient's body contains the genetic material of the organ donor.

Detection and Identification

Identifying a human chimera can be challenging, as the physical manifestations can be subtle or non-existent. Genetic testing is the most reliable method for detecting chimerism. This can include:

• DNA fingerprinting
• Karyotyping
• Next-generation sequencing

Implications

The implications of chimerism in humans vary widely. In some cases, individuals may live their entire lives without knowing they are chimeras. However, chimerism can complicate medical treatments and forensic investigations. For example, a person may have different blood types, leading to confusion in blood transfusion services. In legal contexts, DNA evidence may be misleading if not interpreted with an understanding of the individual's chimeric nature.

Ethical and Legal Considerations

Human chimerism raises several ethical and legal questions, particularly in the realms of identity, parentage, and eligibility for organ transplantation. The legal system may need to adapt to accommodate the unique challenges posed by chimeric individuals, especially in cases involving genetic testing for family relationships.

See Also

• Genetics
• Zygote
• DNA fingerprinting
• Organ transplantation