Genetic Control of Development in Volvox: Isolation and Characterization of Morphogenetic Mutants

Morphogenetic mutants of the colonial green alga, Volvox carteri f. nagariensis, were induced by chemical mutagenesis. The 68 independent mutants are classified into 12 readily identifiable phenotypes affecting various stages of asexual development. Nine of the mutants are temperature sensitive with normal development at 25 degrees and mutant development occurring at 35 degrees. Some mutant genes appear to be involved in the regulation of differentiation or the stability of the differentiated state. Other mutations occur in genes apparently responsible for structural components of dividing cells or adult colonies. Two mutants affect different aspects of the posterior-anterior polarization of the mature colony. One mutation affects a gene which acts very early in colonial development, but affects the appearance of the mature colony. The mutants isolated demonstrate the feasibility of using Volvox to study the genetic control of early steps in embryogenesis.