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Three Domains Of Life
The three-domain system is a taxonomic classification system that groups all cellular life into three domains, namely Archaea, Bacteria and Eukarya, introduced by Carl Woese, Otto Kandler and Mark Wheelis in 1990. The key difference from earlier classifications such as the two-empire system and the five-kingdom classification is the splitting of Archaea (previously named "archaebacteria") from Bacteria as completely different organisms. The three domain hypothesis is considered obsolete by some since it is thought that eukaryotes do not form a separate domain of life; instead, they arose from a fusion between two different species, one from within Archaea and one from within Bacteria. (see Two-domain system) Background Woese argued, on the basis of differences in 16S rRNA genes, that bacteria, archaea, and eukaryotes each arose separately from an ancestor with poorly developed genetic machinery, often called a progenote. To reflect these primary lines of descent, he treated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phylogenetic Tree Of Life 1990 LUCA
In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organisms based on empirical data and observed heritable traits of DNA sequences, protein amino acid sequences, and Morphology (biology), morphology. The results are a phylogenetic tree—a diagram depicting the hypothesis, hypothetical relationships among the organisms, reflecting their inferred evolutionary history. The tips of a phylogenetic tree represent the observed entities, which can be living Taxon, taxa or fossils. A phylogenetic diagram can be rooted or unrooted. A rooted tree diagram indicates the hypothetical common ancestor of the taxa represented on the tree. An unrooted tree diagram (a network) makes no assumption about directionality of character state transformation, and does not show the origin or "root" of the taxa in questi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Progenote
The first universal common ancestor (FUCA) is thought to be a non-cellular entity that was the earliest organism with a genetic code capable of biological translation of RNA molecules into peptides to produce proteins. Its descendants would include the last universal common ancestor (LUCA) and every modern cell. FUCA would also be the ancestor of ancient sister lineages of LUCA, none of which have modern descendants, but which are thought to have horizontally transferred some of their genes into the genome of early descendants of LUCA. FUCA is thought to have been composed of progenotes, proposed ancient biological systems that would have used RNA for their genome and self-replication. By comparison, LUCA would have had a complex metabolism and a DNA genome with hundreds of genes and gene families. Origins Long before the appearance of compartmentalized biological entities like FUCA, life had already begun to organize itself and emerge in a hypothesized pre-cellular era ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Nucleus
The cell nucleus (; : nuclei) is a membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have #Anucleated_cells, no nuclei, and a few others including osteoclasts have Multinucleate, many. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm; and the nuclear matrix, a network within the nucleus that adds mechanical support. The cell nucleus contains nearly all of the cell's genome. Nuclear DNA is often organized into multiple chromosomes – long strands of DNA dotted with various proteins, such as histones, that protect and organize the DNA. The genes within these chromosomes are Nuclear organization, structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prokaryotes
A prokaryote (; less commonly spelled procaryote) is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Greek (), meaning 'before', and (), meaning 'nut' or 'kernel'. In the earlier two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. However, in the three-domain system, based upon molecular phylogenetics, prokaryotes are divided into two domains: Bacteria and Archaea. A third domain, Eukaryota, consists of organisms with nuclei. Prokaryotes evolved before eukaryotes, and lack nuclei, mitochondria, and most of the other distinct organelles that characterize the eukaryotic cell. Some unicellular prokaryotes, such as cyanobacteria, form colonies held together by biofilms, and large colonies can create multilayered microbial mats. Prokaryotes are asexual, reproducing via binary fission. Horizontal gene transfer is comm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Six-kingdom System
In biology, a kingdom is the second highest taxonomic rank In biology, taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of or ..., just below Domain (biology), domain. Kingdoms are divided into smaller groups called Phylum, phyla (singular phylum). Traditionally, textbooks from Canada and the United States have used a system of #Six kingdoms, six kingdoms (Animalia, Plantae, Fungus, Fungi, Protista, Archaea/Archaebacteria, and Bacteria or Eubacteria), while textbooks in other parts of the world, such as Bangladesh, Brazil, Greece, India, Pakistan, Spain, and the United Kingdom have used #Five kingdoms, five kingdoms (Animalia, Plantae, Fungi, Protista and Monera). Some recent classifications based on modern cladistics have explicitly abandoned the term ''kingdom'', noting that some traditional kingdo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Australian Green Tree Frog
The Australian green tree frog (''Ranoidea caerulea''/''Litoria caerulea''), also known as simply green tree frog in Australia, White's tree frog, or dumpy tree frog, is a species of tree frog native to Australia and New Guinea, with Introduced species, introduced populations in the United States and New Zealand, though the latter is believed to have died out. It is morphologically similar to some other members of its genus, particularly the magnificent tree frog (''R. splendida'') and the white-lipped tree frog (''R. infrafrenata''). Larger than most Australian frogs, the Australian green tree frog reaches 10 cm (4 in) or more in length. Its average lifespan in captivity, about 16 years, is long compared with most frogs. Docile and well suited to living near human dwellings, Australian green tree frogs are often found on window sills or inside houses, eating insects drawn by the light. The green tree frog screams when it is in danger to scare off its foe, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
