Yeast reproduces both by vegetative, asexual and sexual methods.
Vegetative reproduction takes place by budding and fission.
Saccharomyces cerevisiae reproduces by budding process in favourable condition.In this process parent cell develop short outgrowth known as bud and nucleus divides in two nuclei. One of them moves towards the bud. When bud enlarges in size their become large constriction between bud and parent cell due to which bud gets detached from parent cell and live as a new yeast cell.
In most favourable conditions, budding process takes place very fast as a result parent cell develops one bud which again develop another bud without detaching from parent cell and a chain like structure is formed which is called pseudo mycelium
In Schizosaccharomycesfission takes place in a favourable condition. In this process parent cell become elongated and transverse wall is formed at centre due to which parent cell divides into daughter cell and each daughter cell live at new yeast cell.
It takes place by the formation of endospores during unfavourable conditions. During this process, the protoplast of the vegetative cells divides into four parts. Each part later becomes surrounded by a thick wall, and act as an endospore.It remains dormant to withstand the adverse conditions. On the return of favourable conditions, the endospores germinate to produce chains of yeast cells.
Haploid diplobiontic life cycle
In Saccharomyces cerevical haploid diplobiontic life cycle is found. In this lifecycle, haploid and diploid phases are equally represented so, this lifecycle is called haploid diplobiontic lifecycle.
A haploid somatic cell can act as gametangia under the scarcity of water and food supply. Fusion of gametangia takes place and a diploid zygote is formed. Zygote changes into a diploid somatic cell and can reproduce by the budding process. Some diploid somatic cells can act as mother cell in which meiosis cell division takes place and four haploid nuclei are formed. This four haploid nuclei changes into Ascospores. Ascospores come out by bursting ascus wall and change into a haploid somatic cell. A haploid somatic cell can reproduce by the budding process and some haploid cell again act as gametangia. In this process, haploid and diploid phase is equally dominant or represented.
Haplobiontic lifecycle is found in Yeast(Schizosaccharomyces endosporous).In this lifecycle, the haploid phase is more represented than the diploid phase.
Diplobiontic lifecycle is found in yeast(Saccharomyces ludwigii). In this lifecycle, the diploid phase is more represented than the haploid phase.
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