Evolutionary history Multicellular organism

1 evolutionary history

1.1 occurrence
1.2 loss of multicellularity
1.3 cancer
1.4 separation of somatic , germ cells

evolutionary history



















































































































































































occurrence

multicellularity has evolved independently @ least 46 times, including in prokaryotes, cyanobacteria, myxobacteria, actinomycetes, magnetoglobus multicellularis or methanosarcina. however, complex multicellular organisms evolved in 6 eukaryotic groups: animals, fungi, brown algae, red algae, green algae, , land plants. evolved repeatedly chloroplastida (green algae , land plants), once or twice animals, once brown algae, 3 times in fungi (chytrids, ascomycetes , basidiomycetes) , perhaps several times slime molds , red algae. first evidence of multicellularity cyanobacteria-like organisms lived 3–3.5 billion years ago. reproduce, true multicellular organisms must solve problem of regenerating whole organism germ cells (i.e. sperm , egg cells), issue studied in evolutionary developmental biology. animals have evolved considerable diversity of cell types in multicellular body (100–150 different cell types), compared 10–20 in plants , fungi.

loss of multicellularity

loss of multicellularity occurred in groups. fungi predominantly multicellular, though diverging lineages largely unicellular (e.g. microsporidia) , there have been numerous reversions unicellularity across fungi (e.g. saccharomycotina, cryptococcus, , other yeasts). may have occurred in red algae (e.g. porphyridium), possible primitively unicellular. loss of multicellularity considered probable in green algae (e.g. chlorella vulgaris , ulvophyceae). in other groups, parasites, reduction of multicellularity occurred, in number or types of cells (e.g. myxozoans, multicellular organisms, earlier thought unicellular, extremely reduced cnidarians).

cancer

multicellular organisms, long-living animals, face challenge of cancer, occurs when cells fail regulate growth within normal program of development. changes in tissue morphology can observed during process. cancer in animals (metazoans) has been described loss of multicellularity. there discussion possibility of existence of cancer in other multicellular organisms or in protozoa. example, plant galls have been characterized tumors authors argue plants not develop cancer.

separation of somatic , germ cells

in multicellular groups, called weismannists, separation between sterile somatic cell line , germ cell line evolved. however, weismannist development relatively rare (e.g. vertebrates, arthropods, volvox), great part of species have capacity somatic embryogenesis (e.g. land plants, algae, many invertebrates).