Molecular cell biological studies on the evolution of male and female sex in algae.

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Spatial arrangement of gamete fusion site or mating structure was studied in ulvophycean green algae, Chaetomorpha spiralis, Monostroma angicava and chlorophycean green alga Gonium pectoral using electron microsco py. In all species, cell fusion site of the gamete was located on the same side of the eyespot in one sex type while it was located on the other side of the eyespot in the opposite mating type. These results support the proposal that sex specific arrangement of cell fusion site or mating structure may be a universal feature in chlorophyte algae. The relationship between the sex determination gene MID and sex specific arrangement of mating structure was studied using G. pectorale. In the MID+ gametes, mating structure was present on the same side as the eyespot while in the MID- gametes mating structure was present on the opposite side of the eyespot. These results are consistent with that of Chlamydmonas reinhardtii and suggest that the close relationship between presence or absence of MID and sex specific arrangement of mating structure in these algae.