The spirogyre is a green Algue of Fresh water, being appeared as Filament S.

Biological cycle

In the biological cycle of the spirogyre,

• concerning the cytological alternace of phase, the Méiose intervenes just after the Fécondation. The Haplophase is thus more important than the Diplophase, reduced to the Zygote. It is about a cycle haplophasic .
• concerning the morphological alternation of generations, this cycle comprises only one generation: méiospore with fecundation (not of generation enters the zygote and the formation of the spores). It is about a cycle monogenetic .

Reproduction

The spirogyre is an good example of conjugation; it reproduces, in a sexuée way, by exchanging DNA between two cell S. Some Filament S, in a whole of parallel filaments, play the part of the female, and others that of the male. The cells of adjacent filaments develop tubular extensions which grow one towards the other and amalgamate finally to form a continuous tube between the two cells. In same time, the contents of each cell formed a sphere. The spheres of the male filament, after being itself cut through a path through the tube, amalgamate with a sphere of a female cell in the other filament. The result of this Fécondation is a Zygote (zygospore) in the filament female. After one period of weak activity, the zygote undergoes a Méiose and Germe, creating a new filament.

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