megasporogenesis
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megaspores...megasporogenesisTRANSCRIPT
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MEGASPOROGENESIS
MUHAMMED SADIQ
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MEGASPORES•Megaspores also called macrospores are a type of
spore found in heterosporous plants
•Megaspores which germinates into a female gametophyte which produces egg cells
• These are fertilized by the male gametophyte developing from the microspore
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MEGASPOROGENESIS
•Megasporogenesis is the formation of megaspores
•Megaspores are formed inside the ovule of seed plants
• A diploid cell in the ovule called megasporocyte
• Megaspore mothercell undergoes meiosis and give raise to four haploid megaspores
• In most plants only one of the megaspores develop into megagametophyte and other 3 disintegrates
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• In gymnosperms and flowering plants the megaspore is produced inside the nucellus of the ovule
• Angiosperms exhibit three patterns of megasporogenesis , monosporic, bisporic,and tetrasporic.
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• The megasporocyte enlarges and its cytoplasm become very dense, the nucleus enlarges in preparation for meiosis.
• The integuments develops from the ovule epidermis
• These envalops the megagametophyte and it become incomplete and leave a micropyle through which pollen tubes enters later.
• Two haploid nucei are then created.
• These divide again to produce a cell with four nuclei.
• The four haploid nuclei divide again to produce a cell with eight nuclei this process is called free nuclear division
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• Following nuclear migrations and cell formation , the mature megagametophyte ie, embryo sac id formed
• It is typically composed of an egg apparatus ( egg+2synergids) at the micropylar end of the megagametophyte.
• Three antipodals are found at the chalazal end of the megagametophyte
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