Chimera (genetics)

A genetic chimerism or chimera (/kaɪˈmɪərə/ ky-MEER-ə or /kɪˈmɪərə/ kim-EER-ə) is a single organism composed of cells with more than one distinct genotype. Animal chimeras can be produced by the merger of two (or more) embryos. In plants and some animal chimeras, mosaicism involves distinct types of tissue that originated from the same zygote but differ due to mutation during ordinary cell division.

Normally, genetic chimerism is not visible on casual inspection; however, it has been detected in the course of proving parentage.^[1] More practically, in agronomy Chimera indicates a plant or portion of a plant whose tissues are made up of two or more types of cells with different genetic makeup; it can derive from a bud mutation or, more rarely, at the grafting point, from the concrescence of cells of the two bionts; in this case it is commonly referred to as a "graft hybrid", although it is not a hybrid in the genetic sense of "hybrid".^[2]

In contrast, an individual where each cell contains genetic material from two organisms of different breeds, varieties, species or genera is called a hybrid.^[3]

Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from a different genome. For example, transplantation of bone marrow often determines the recipient's ensuing blood type.^[4]