Meiosis, blade development and sex determination in Porphyra umbilicalis (L.) J. Agardh from Avonport, Nova Scotia, Canada

Recently, conclusive evidence of sexual reproduction, and the discovery that meiosis occurs in the germinating conchospores for several species of Porphyra C. Ag. has renewed interest in studying this genus. The intriguing sexually divided morphology of Porphyra umbilicalis (L.) J. Agardh from the mudflats of Avonport, Nova Scotia, prompted me to hypothesize that sex expression P. umbilicalis and other striped Porphyras may result from genetic segregation of a pair of sex-determining alleles during early sporeling development, presumably at meiosis.;The present thesis constitutes an investigation of this hypothesis using P. umbilicalis. Meiosis in the germinating conchospore resulting in a meiotic tetrad was confirmed by karyological observations. Second, stable color mutants of P. umbilicalis were used as genetic markers demonstrating that the bulk of the mature blade is derived from the two anticlinally divided upper cells of the germinating sporeling. Last, by comparing cell lineage boundaries laid down by the segregation of color mutations at meiosis with those defined by sexual differentiation on the same fronds, strong evidence is given that sex-determination is also controlled by segregating genetic factors with no genetic linkage between any of the color mutations and the putative sex-determining alleles.