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Holocentric Chromosomes
Holocentric chromosomes are chromosomes that possess multiple kinetochores along their length rather than the single centromere typical of other chromosomes. They were first described in cytogenetic experiments in 1935. Since this first observation, the term holocentric chromosome has referred to chromosomes that: i) lack the primary constriction corresponding to the centromere observed in monocentric chromosomes; and ii) possess multiple kinetochores dispersed along the entire chromosomal axis, such that microtubules bind to the chromosome along its entire length and move broadside to the pole from the metaphase plate. Holocentric chromosomes are also termed ''holokinetic'', because, during cell division, the sister chromatids move apart in parallel and do not form the classical V-shaped figures typical of monocentric chromosomes. Holocentric chromosomes have evolved several times during both animal and plant evolution, and are currently reported in about eight hundred diverse spe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome
A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most important of these proteins are the histones. Aided by chaperone proteins, the histones bind to and condense the DNA molecule to maintain its integrity. These eukaryotic chromosomes display a complex three-dimensional structure that has a significant role in transcriptional regulation. Normally, chromosomes are visible under a light microscope only during the metaphase of cell division, where all chromosomes are aligned in the center of the cell in their condensed form. Before this stage occurs, each chromosome is duplicated ( S phase), and the two copies are joined by a centromere—resulting in either an X-shaped structure if the centromere is located equatorially, or a two-armed structure if the centromere is located distally; the jo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cytology
Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and functioning of organisms. Cell biology is the study of the structural and functional units of cells. Cell biology encompasses both prokaryotic and eukaryotic cells and has many subtopics which may include the study of cell metabolism, cell communication, cell cycle, biochemistry, and cell composition. The study of cells is performed using several microscopy techniques, cell culture, and cell fractionation. These have allowed for and are currently being used for discoveries and research pertaining to how cells function, ultimately giving insight into understanding larger organisms. Knowing the components of cells and how cells work is fundamental to all biological sciences while also being essential for research in biomedical fields ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aphids
Aphids are small sap-sucking insects in the Taxonomic rank, family Aphididae. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Eriosomatinae, woolly aphids. A typical life cycle involves flightless females giving Viviparity, live birth to female Nymph (biology), nymphs—who may also be already Pregnancy, pregnant, an adaptation scientists call telescoping generations—without the involvement of males. Developmental biology, Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Alate, Winged females may develop later in the season, allowing the insects to colonize new plants. In Temperate climate, temperate regions, a phase of sexual reproduction occurs in the autumn, with the insects often overwintering as eggs. The life cycle of some species involves an alternation between two species of host plants, for example between an annual crop and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phytophagous
A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet (nutrition), diet. These more broadly also encompass animals that eat non-vascular plant, non-vascular autotrophs such as mosses, algae and lichens, but do not include those feeding on decomposition, decomposed detritus, plant matters (i.e. detritivores) or macrofungi (i.e. fungivores). As a result of their plant-based diet, herbivorous animals typically have mouth structures (jaws or arthropod mouthparts, mouthparts) well adaptation, adapted to comminution, mechanically break down plant materials, and their digestive systems have special enzymes (e.g. amylase and cellulase) to digest polysaccharides. Grazing (behaviour), Grazing herbivores such as horses and cattles have wide flat-crown (tooth), crowned teeth that are better adapted for grinding grass, tree bark and other tougher lignin-conta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the population during that process. Thirdly, it is a phenotypic trait or adaptive trait, with a functional role in each individual organism, that is maintained and has evolved through natural selection. Historically, adaptation has been described from the time of the ancient Greek philosophers such as Empedocles and Aristotle. In 18th and 19th-century natural theology, adaptation was taken as evidence for the existence of a deity. Charles Darwin and Alfred Russel Wallace proposed instead that it was explained by natural selection. Adaptation is related to biological fitness, which governs the rate of evolution as measured by changes in allele frequencies. Often, two or more species co-adapt and co-evolve as they develop adaptations tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neoptera
Neoptera (Ancient Greek ''néos'' ("new") + ''pterón'' ("wing")) is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the more basal orders of winged insects (the " Palaeoptera" assemblage), which are unable to flex their wings in this way. Classification The taxon Neoptera was proposed by А.М. Martynov in 1923 and 1924, in the following classification: Pterygota *division Palaeoptera **order Odonata **order Agnatha (correct name: Ephemeroptera) **†order Dictyoneuridea **†order Megasecoptera **†order Meganisoptera **†order Protephemeroidea *division Neoptera **superorder Endopterygota ***order Coleoptera ***order Strepsiptera ***order Neuroptera ***order Raphidioptera ***order Megaloptera ***order Diptera ***order Mecoptera ***order Trichoptera ***order Lepidoptera ***order Hymenoptera **subdivision Polyneoptera ***superorder Orthopteroid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monocentric Chromosome
The monocentric chromosome is a chromosome that has only one centromere in a chromosome and forms a narrow constriction. Monocentric centromeres are the most common structure on highly repetitive DNA in plants and animals. Structure Monocentric chromosomes as compared to holocentric chromosomes where the entire length of the chromosome acts as the centromere. In monocentric chromosomes there is one primary constriction and the centromere its CenH3 loci at this location. Holocentric chromosomes are found throughout the plant and animal kingdoms such as the nematode ''Caenorhabditis elegans''. Holocentric chromosomes do have an evolutionary advantage by preventing the loss of chromosome after a DNA double-strand break. The centromere is the point of attachment for the mitotic apparatus Chromosomal aberrations Deletions, duplications and translocations can produce a polycentric chromosome. This is troublesome for cells that divide often since at the time of anaphase the pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Convergent Evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. The cladistic term for the same phenomenon is Cladogram#Homoplasies, homoplasy. The recurrent evolution of flight is a classic example, as flying pterygota, insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Functionally similar features that have arisen through convergent evolution are ''analogous'', whereas ''homology (biology), homologous'' structures or traits have a common origin but can have dissimilar functions. Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions. The opposite of convergence is divergent evolution, where related species evolve different trai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nematodes
The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (helminths) are the cause of soil-transmitted helminthiases. They are classified along with arthropods, tardigrades and other moulting animals in the clade Ecdysozoa. Unlike the flatworms, nematodes have a tubular digestive system, with openings at both ends. Like tardigrades, they have a reduced number of Hox genes, but their sister phylum Nematomorpha has kept the ancestral protostome Hox genotype, which shows that the reduction has occurred within the nematode phylum. Nematode species can be difficult to distinguish from one another. Consequently, estimates of the number of nematode species are uncertain. A 2013 survey of animal biodiversity suggested there are over 25,000. Estimates of the total number of extant species are subject ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arachnids
Arachnids are arthropods in the class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons. Adult arachnids have eight legs attached to the cephalothorax. In some species the frontmost pair of legs has converted to a sensory function, while in others, different appendages can grow large enough to take on the appearance of extra pairs of legs. Almost all extant arachnids are terrestrial, living mainly on land. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 110,000 named species, of which 51,000 are species of spiders. The term is derived from the Greek word (''aráchnē'', 'spider'), from the myth of the hubristic human weaver Arachne, who was turned into a spider. Morphology Almost all adult arachnids have eight legs, unlike adult insects whic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plant
Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars from carbon dioxide and water, using the green pigment chlorophyll. Exceptions are parasitic plants that have lost the genes for chlorophyll and photosynthesis, and obtain their energy from other plants or fungi. Most plants are multicellular organism, multicellular, except for some green algae. Historically, as in Aristotle's biology, the plant kingdom encompassed all living things that were not animals, and included algae and fungi. Definitions have narrowed since then; current definitions exclude fungi and some of the algae. By the definition used in this article, plants form the clade Viridiplantae (green plants), which consists of the green algae and the embryophytes or land plants (hornworts, liverworts ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
