How many divisions shall be required for flrmation of embryo sac from megaspore mother cell in polysonum?
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There are three known kind of embryo sacs according to the number of megaspores involved in formation of embryo sac-
Monosporic: In this type of development 3 megaspores of tetrad get degenerate one remain functional and forms embryosac, e.g. Polygonum
Bisporic: when two megasporic nuclei takes part in formation of embryosac. Both the nuclei are genetically different. They arise due to any defect in cytokinesis in either meiosis I or meiosis II, e.g. Alium
Tetrasporic: In this type due to failure of cytokinesis I and II a four nucleate coenomegaspore tetrad is formed and all 4 nuclei participate in formation of embryosac.
Now coming to your question, development of a particular type of embryo sac depends upon the number of megaspores participating in the process. Meiotic division of a single megaspore mother cell always gives rise to four megaspore nuclei. Therefore whether it is a monosporic or a tetrasporic embryo sac, only one megaspore mother cell is required.
Monosporic: In this type of development 3 megaspores of tetrad get degenerate one remain functional and forms embryosac, e.g. Polygonum
Bisporic: when two megasporic nuclei takes part in formation of embryosac. Both the nuclei are genetically different. They arise due to any defect in cytokinesis in either meiosis I or meiosis II, e.g. Alium
Tetrasporic: In this type due to failure of cytokinesis I and II a four nucleate coenomegaspore tetrad is formed and all 4 nuclei participate in formation of embryosac.
Now coming to your question, development of a particular type of embryo sac depends upon the number of megaspores participating in the process. Meiotic division of a single megaspore mother cell always gives rise to four megaspore nuclei. Therefore whether it is a monosporic or a tetrasporic embryo sac, only one megaspore mother cell is required.
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