Chimarism

Chimera (medical def):in medicine, a person composed of two genetically distinct types of cells. Human chimeras were first discovered with the advent of blood typing when it was found that some people had more than one blood type 1. This condition can be compared to Mosaicism. However, the words cannot be used synonymously as chimarism is far more rare and is often encountered in experimental embryology.2

Properties
"Chimeric cattle are not at all rare. When a cow has twins, it is almost inevitable that anastomoses (areas of joining) develop between the fetal circulatory systems early in gestation. This leads to exchange of blood between the two fetuses. Fetal blood contains hematopoietic stem cells, and each fetus is permanently "seeded" with stem cells from its twin"(2, first paragraph)