(1) Reproduction of unicellular organisms by budding. (2) Development of an embryo during cleavage and germ layer formation. (3) Transformation of small lymphocytes of human peripheral blood in tissue culture into large, morphologically primordial blastlike cells capable of undergoing mitosis; can be induced by various agents including phytohemagglutinin, concanavalin A, certain antigens to which the cell donor has been previously immunized, and leukocytes from an unrelated individual. [blasto- + G. genesis, origin]