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Whole-genome Duplication
Paleopolyploidy is the result of genome duplications which occurred at least several million years ago (MYA). Such an event could either double the genome of a single species ( autopolyploidy) or combine those of two species (allopolyploidy). Because of functional redundancy, genes are rapidly silenced or lost from the duplicated genomes. Most paleopolyploids, through evolutionary time, have lost their polyploid status through a process called diploidization, and are currently considered diploids e.g. baker's yeast, '' Arabidopsis thaliana'', and perhaps humans. Paleopolyploidy is extensively studied in plant lineages. It has been found that almost all flowering plants have undergone at least one round of genome duplication at some point during their evolutionary history. Ancient genome duplications are also found in the early ancestor of vertebrates (which includes the human lineage) near the origin of the bony fishes, and another in the stem lineage of teleost fishes. Ev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleopolyploidy
Paleopolyploidy is the result of genome duplications which occurred at least several million years ago (MYA). Such an event could either double the genome of a single species ( autopolyploidy) or combine those of two species (allopolyploidy). Because of functional redundancy, genes are rapidly silenced or lost from the duplicated genomes. Most paleopolyploids, through evolutionary time, have lost their polyploid status through a process called diploidization, and are currently considered diploids e.g. baker's yeast, '' Arabidopsis thaliana'', and perhaps humans. Paleopolyploidy is extensively studied in plant lineages. It has been found that almost all flowering plants have undergone at least one round of genome duplication at some point during their evolutionary history. Ancient genome duplications are also found in the early ancestor of vertebrates (which includes the human lineage) near the origin of the bony fishes, and another in the stem lineage of teleost fishes. Ev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amborella Trichopoda
''Amborella'' is a monotypic genus of understory shrubs or small trees endemic to the main island, Grande Terre, of New Caledonia in the southwest Pacific Ocean. The genus is the only member of the family Amborellaceae and the order Amborellales and contains a single species, ''Amborella trichopoda''. ''Amborella'' is of great interest to plant systematists because molecular phylogenetic analyses consistently place it as the sister group to all other flowering plants. Description ''Amborella'' is a sprawling shrub or small tree up to high. It bears alternate, simple evergreen leaves without stipules. The leaves are two-ranked, with distinctly serrated or rippled margins, and about long. ''Amborella'' has xylem tissue that differs from that of most other flowering plants. The xylem of ''Amborella'' contains only tracheids; vessel elements are absent. Xylem of this form has long been regarded as a primitive feature of flowering plants. The species is dioecious. This mea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homeolog
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei ( eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains one or more chromosomes and comes from each of two parents, resulting in pairs of homologous chromosomes between sets. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid somatic cells, but produce haploid gametes (eggs and sperm) by meiosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of bees and other Hymenoptera, for example, are monoploid. Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis, the sporophyte generation is diploid and produces spores by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene Duplication
Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage. Mechanisms of duplication Ectopic recombination Duplications arise from an event termed unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The chance of it happening is a function of the degree of sharing of repetitive elements between two chromosomes. The products of this recombination are a duplication at the site of the exchange and a reciprocal deletion. Ectopic recombination ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Clock
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins. The benchmarks for determining the mutation rate are often fossil or archaeological dates. The molecular clock was first tested in 1962 on the hemoglobin protein variants of various animals, and is commonly used in molecular evolution to estimate times of speciation or radiation. It is sometimes called a gene clock or an evolutionary clock. Early discovery and genetic equidistance The notion of the existence of a so-called "molecular clock" was first attributed to Émile Zuckerkandl and Linus Pauling who, in 1962, noticed that the number of amino acid differences in hemoglobin between different lineages changes roughly linearly with time, as estimated from fossil evi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sequence Homology
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a speciation event (orthologs), or a duplication event (paralogs), or else a horizontal (or lateral) gene transfer event (xenologs). Homology among DNA, RNA, or proteins is typically inferred from their nucleotide or amino acid sequence similarity. Significant similarity is strong evidence that two sequences are related by evolutionary changes from a common ancestral sequence. Alignments of multiple sequences are used to indicate which regions of each sequence are homologous. Identity, similarity, and conservation The term "percent homology" is often used to mean "sequence similarity”, that is the percentage of identical residues (''percent identity''), or the percentage of residues conserved with similar physicochemical properties ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kluyveromyces Marxianus
''Kluyveromyces marxianus'' in ascomycetous yeast and member of the genus, ''Kluyveromyces''. It is the sexual stage of '' Atelosaccharomyces pseudotropicalis'' also known as '' Candida kefyr''. This species has a homothallic mating system and is often isolated from dairy products. History Taxonomy This species was first described in the genus '' Saccharomyces'' as ''S. marxianus'' by the Danish mycologist, Emil Christian Hansen from beer wort. He named the species for the zymologist, Louis Marx of Marseille who first isolated it from grape. The species was transferred to the genus ''Kluyveromyces'' by van der Walt in 1956. Since then, 45 species have been recognized in this genus. The closest relative of ''Kluyveromyces marxianus'' is the yeast '' Kluyveromyces lactis'', often used in the dairy industry. Both ''Kluyveromyces'' and ''Saccharomyces'' are considered a part of the "''Sacchromyces'' complex", subclade of the Saccharomycetes. Using 18S rRNA gene sequencing, it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kluyveromyces Lactis
''Kluyveromyces lactis'' is a '' Kluyveromyces'' yeast commonly used for genetic studies and industrial applications. Its name comes from the ability to assimilate lactose and convert it into lactic acid. ''Kluyveromyces lactis'' (formerly ''Saccharomyces lactis'') is a yeast which has the ability to assimilate lactose and convert it into lactic acid. ''K. lactis'' and other organisms i.e., ''Aspergillus niger'' var awamori and ''Escherichia coli'' K-12 are grown in fermenters to produce chymosin ( rennet) on a commercial scale; this rennet, which replaces the conventional form obtained from slaughtered animals, is now widely used in cheese production. Yeasts and fungi are ideal organisms for comparative genomic studies in eukaryotes because of their small and compact genomes and because they include a number of species such as ''Neurospora crassa'', ''Saccharomyces cerevisiae'' and ''Schizosaccharomyces pombe'', that have been, and continue to be, used extensively in genetic s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2R Hypothesis
The 2R hypothesis or Ohno's hypothesis, first proposed by Susumu Ohno in 1970,Ohno, Susumu (1970). ''Evolution by Gene Duplication.'' London: Allen and Unwin, . is a hypothesis that the genomes of the early vertebrate lineage underwent two complete genome duplications, and thus modern vertebrate genomes reflect paleopolyploidy. The name derives from the ''2 rounds'' of duplication originally hypothesized by Ohno, but refined in a 1994 version, and the term ''2R hypothesis'' was probably coined in 1999. Variations in the number and timings of genome duplications typically still are referred to as examples of the 2R hypothesis. The 2R hypothesis has been the subject of much research and controversy; however, with growing support from genome data, including the human genome, the balance of opinion has shifted strongly in favour of support for the hypothesis. According to Karsten Hokamp, Aoife McLysaght and Kenneth H. Wolfe, the version of the genome duplication hypothesis from which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brassica
''Brassica'' () is a genus of plants in the cabbage and mustard family ( Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, or mustard plants. Crops from this genus are sometimes called ''cole crops''derived from the Latin ''caulis'', denoting the stem or stalk of a plant. The genus ''Brassica'' is known for its important agricultural and horticultural crops and also includes a number of weeds, both of wild taxa and escapees from cultivation. ''Brassica'' species and varieties commonly used for food include bok choy, broccoli, cauliflower, cabbage, choy sum, kohlrabi, napa cabbage, rutabaga, turnip and some seeds used in the production of canola oil and the condiment mustard. Over 30 wild species and hybrids are in cultivation, plus numerous cultivars and hybrids of cultivated origin. Most are seasonal plants ( annuals or biennials), but some are small shrubs. ''Brassica'' plants have been the subject of much scientific i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asterids
In the APG IV system (2016) for the classification of flowering plants, the name asterids denotes a clade (a monophyletic group). Asterids is the largest group of flowering plants, with more than 80,000 species, about a third of the total flowering plant species. Well-known plants in this clade include the common daisy, forget-me-nots, nightshades (including potatoes, eggplants, tomatoes, chili peppers and tobacco), the common sunflower, petunias, yacon, morning glory, sweet potato, coffee, lavender, lilac, olive, jasmine, honeysuckle, ash tree, teak, snapdragon, sesame, psyllium, garden sage, table herbs such as mint, basil, and rosemary, and rainforest trees such as Brazil nut. Most of the taxa belonging to this clade had been referred to as Asteridae in the Cronquist system (1981) and as Sympetalae in earlier systems. The name asterids (not necessarily capitalised) resembles the earlier botanical name but is intended to be the name of a clade rather than a form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
