BIOL 215 Lecture Notes - Lecture 8: Sickle-Cell Disease, Outcrossing, Aegilops
11 Mar 2013
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Document Summary
Plants: a story of transition from water to land: they evolved from green algae (aquatic seaweed, plates are multicellular eukaryotes, possess cellulose rich cell walls, they are photoautotrophic, alternation of generations. Unicellular green algae that had incorporated new genes through horizontal gene transfer and gained organelles by endosymbiosis, transformed into multicellular photosynthetic organisms. An alternation of generation includes the sporophyte - diploid stage (2n) to a gametophyte - haploid stage (n) Sperm and egg are haploids which when they go together, become a zygote that is diploid. 4 major evolutionary inventions in plants: silurian (430 mya): origin of plants, early devonian (390 mya): vascular lineage, late devonian(360 mya): seed lineage, early cretaceous (130 mya): flower lineage. Moving onto land required three evolutionary changes: reduction in the size of the gametophyte, evolution of easily dispersible pollen, and encasement of spores in seeds, this allowed plants to avoid desiccation and so move away from water.
