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Developmental Selection
Developmental selection is selection that occurs on developmental units in an organism, such as cell lineages, embryos, and gametes or gametophytes. Generally, developmental selection is differentiated from natural selection because the targets of selection are internal to an organism contain the developmental units, rather than selection due to external environmental factors that favor specific phenotypes. However, in animals, developmental selection against offspring can manifest in the external environment, in which parents might select against offspring with developmental instabilities, or when offspring with deleterious malformations may not survive. Developmental selection in plants Selective embryo abortion A common form of developmental selection in plants is selective ovule abortion, where the maternal parent selects against unstable embryos. Abortion of low-viability offspring may be driven by either genetic factors or environmental stress. Developmental selection may ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which in his view is intentional, whereas natural selection is not. Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits. The environment of a genome includes the molecular biology in the cell, other cells, other individuals, populations, species, as well as the abiotic environment. Because individuals with certain variants of the trait tend to survive and reproduce more than individual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apical Meristem In Allium Root Tip (34886440510)
Apical means "pertaining to an apex". It may refer to: * Apical ancestor, refers to the last common ancestor of an entire group, such as a species (biology) or a clan (anthropology) *Apical (anatomy), an anatomical term of location for features located opposite the base of an organism or structure * Apical (chemistry), a position in certain molecular geometries in chemistry * Apical (dentistry), direction towards the root tip of a tooth * Apical consonant, a consonant produced with the tip of the tongue * Apical dendrite, a type of dendrite found on pyramidal neurons * Apical dominance, the phenomenon whereby the main, central stem of a plant is dominant over other side stems *Apical membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ..., in cell biology the surface of a plasma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selective Embryo Abortion
Selective embryo abortion (also known as selective seed abortion and selective ovule abortion ), is a form of non-random, premature termination of embryonic development in plants. Selective embryo abortion assumes that embryo termination depends on the genetic quality of seeds developing within an ovary, and predicts that successfully matured seeds will be of greater fitness than aborted seeds. Consequently, selective embryo abortion has the potential to act as a unique stage of natural selection, influencing the evolution of plant populations and species. This concept was described by botanist John T. Buchholz in 1922 under his framework of developmental selection, which referred to selective embryo abortion as “interovular selection.” Selective embryo abortion may result from competition among embryos for maternal resources. The maternal plant may also play an active role by recognizing and selectively aborting genetically inferior embryos. Evidence of offspring fitness ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gametophytic Selection
Gametophytic selection is the selection of one haploid pollen grain over another through the means of pollen competition (see also certation), and that resulting sporophytic generations are positively affected by this competition. Evidence for the positive effects of gametophytic selection on the sporophyte generation has been observed in several flowering plant species, but there are is still some debate as to the biological significance of gametophytic selection. Non-random success of pollen tubes Pollen competition hypothesis The competitive ability of pollen grains ( microgapmetophytes) is rooted in the expression of their haploid genomes. The haploid genes are expressed immediately after pollen development and during pollen germination and pollen-tube growth. About 60% of genes expressed in the sporophyte are also expressed in the microgametophyte. This expression influences the ability of pollen tubes to compete during growth. When pollen competition occurs, the competi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-incompatibility
Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial ( herkogamy) and temporally ( dichogamy) separation. SI is best-studied and particularly common in flowering plants, although it is present in other groups, including sea squirts and fungi. In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a matching allele or genotype, the process of pollen germination, pollen-tube growth, ovule fertilization, or embryo development is inhibited, and consequently no seeds are produced. SI is one of the most important means of preventing inbreeding and promoting the generation of new genotypes in plants and it is considered one of the causes of the spread and success of angiosperms on Earth. Mec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Lineage Selection
Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery with only a few monks or nuns * Prison cell, a room used to hold people in prisons Groups of people * Cell, a group of people in a cell group, a form of Christian church organization * Cell, a unit of a clandestine cell system, a penetration-resistant form of a secret or outlawed organization * Cellular organizational structure, such as in business management Science, mathematics, and technology Computing and telecommunications * Cell (EDA), a term used in an electronic circuit design schematics * Cell (microprocessor), a microprocessor architecture developed by Sony, Toshiba, and IBM * Memory cell (computing), the basic unit of (volatile or non-volatile) computer memory * Cell, a unit in a database table or spreadsheet, formed by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emporer Scorpion
An emperor (from la, imperator, via fro, empereor) is a monarch, and usually the sovereign ruler of an empire or another type of imperial realm. Empress, the female equivalent, may indicate an emperor's wife ( empress consort), mother (empress dowager), or a woman who rules in her own right and name ( empress regnant). Emperors are generally recognized to be of the highest monarchic honor and rank, surpassing kings. In Europe, the title of Emperor has been used since the Middle Ages, considered in those times equal or almost equal in dignity to that of Pope due to the latter's position as visible head of the Church and spiritual leader of the Catholic part of Western Europe. The Emperor of Japan is the only currently reigning monarch whose title is translated into English as "Emperor". Both emperors and kings are monarchs or sovereigns, but both emperor and empress are considered the higher monarchical titles. In as much as there is a strict definition of emperor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution Of Animals
The history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to present day. Earth formed about 4.5 billion years ago (abbreviated as ''Ga'', for ''gigaannum'') and evidence suggests that life emerged prior to 3.7 Ga. Although there is some evidence of life as early as 4.1 to 4.28 Ga, it remains controversial due to the possible non-biological formation of the purported fossils. The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor. Only a very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species. * However, only 1.75–1.8 million have been named "A version of this article appears in print on Nov. 9, 2014, Section SR, Page 6 of the New York edition with the headline: Prehistory's Brilliant Future." and 1.8 million documented in a central database. These currently ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
