Single‐Born Marmosets without Hemopoietic Chimerism: Naturally Occurring and Induced 1

Marmosets have a high frequency of fraternal twinning, and placental vascular anastomoses between the twin fetuses invariably lead to hemopoietic chimerism. The occasional finding of chimerism in single‐born marmosets suggested that in a twin pregnancy one fetus had undergone resorption after contributing hemopoietic stem cells to its twin. In this study non‐chimeric single‐born marmosets were produced by fallopian tube ligation or surgical relocation of one ovary in breeding females. Further, in an examination of hemopoietic cells from over 50 single‐born young from nonoperated females, chimerism occurred less frequently than what one would expect if resorption of a co‐twin had occurred after a functional anastomosis had been established.