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Overlapping Generations
In population genetics overlapping generations refers to mating systems where more than one breeding generation is present at any one time. In systems where this is not the case there are non-overlapping generations (or discrete generations) in which every breeding generation lasts just one breeding season. If the adults reproduce over multiple breeding seasons the species is considered to have overlapping generations. Examples of species which have overlapping generations are many mammals, including humans, and many invertebrates in seasonal environments. Examples of species which consist of non-overlapping generations are annual plants and several insect species. Non-overlapping generations is one of the characteristics that needs to be met in the Hardy–Weinberg model for evolution to occur. This is a very restrictive and unrealistic assumption, but one that is difficult to dispose of. Overlapping versus non-overlapping generations In population genetics models, such as th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Population Genetics
Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as Adaptation (biology), adaptation, speciation, and population stratification, population structure. Population genetics was a vital ingredient in the emergence of the Modern synthesis (20th century), modern evolutionary synthesis. Its primary founders were Sewall Wright, J. B. S. Haldane and Ronald Fisher, who also laid the foundations for the related discipline of quantitative genetics. Traditionally a highly mathematical discipline, modern population genetics encompasses theoretical, laboratory, and field work. Population genetic models are used both for statistical inference from DNA sequence data and for proof/disproof of concept. What sets population genetics apart from newer, more phenotypic approaches to modelling evolution, such as evolutionary game theory and evo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks, annelids, echinoderms and cnidarians. The majority of animal species are invertebrates; one estimate puts the figure at 97%. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata. Invertebrates vary widely in size, from 50 μm (0.002 in) rotifers to the 9–10 m (30–33 ft) colossal squid. Some so-called invertebrates, such as the Tunicata and Cephalochordata, are more closely related to vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy. Etymology The word "invertebrate" comes from the Latin word ''vertebra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annual Plant
An annual plant is a plant that completes its life cycle, from germination to the production of seeds, within one growing season, and then dies. The length of growing seasons and period in which they take place vary according to geographical location, and may not correspond to the four traditional seasonal divisions of the year. With respect to the traditional seasons, annual plants are generally categorized into summer annuals and winter annuals. Summer annuals germinate during spring or early summer and mature by autumn of the same year. Winter annuals germinate during the autumn and mature during the spring or summer of the following calendar year. One seed-to-seed life cycle for an annual plant can occur in as little as a month in some species, though most last several months. Oilseed rapa can go from seed-to-seed in about five weeks under a bank of fluorescent lamps. This style of growing is often used in classrooms for education. Many desert annuals are therophytes, b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hardy–Weinberg Principle
In population genetics, the Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem, or law, states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. These influences include ''genetic drift'', '' mate choice'', ''assortative mating'', ''natural selection'', ''sexual selection'', ''mutation'', ''gene flow'', '' meiotic drive'', ''genetic hitchhiking'', ''population bottleneck'', ''founder effect,'' ''inbreeding and outbreeding depression''. In the simplest case of a single locus with two alleles denoted ''A'' and ''a'' with frequencies and , respectively, the expected genotype frequencies under random mating are for the AA homozygotes, for the aa homozygotes, and for the heterozygotes. In the absence of selection, mutation, genetic drift, or other forces, allele frequencies ''p'' and ''q'' are constant between generations, so equilibriu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules. The theory of evolut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Altruism
Altruism is the principle and moral practice of concern for the welfare and/or happiness of other human beings or animals, resulting in a quality of life both material and spiritual. It is a traditional virtue in many cultures and a core aspect of various religious and secular worldviews. However, the object(s) of concern vary among cultures and religions. In an extreme case, altruism may become a synonym of selflessness, which is the opposite of selfishness. The word "altruism" was popularized (and possibly coined) by the French philosopher Auguste Comte in French, as ''altruisme'', for an antonym of egoism. He derived it from the Italian ''altrui'', which in turn was derived from Latin ''alteri'', meaning " other people" or "somebody else". Altruism in biological observations in field populations of the day organisms is an individual performing an action which is at a cost to themselves (e.g., pleasure and quality of life, time, probability of survival or reproductio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amegilla Dawsoni
''Amegilla dawsoni'', sometimes called the Dawson's burrowing bee, is a species of bee that nests by the thousands in arid claypans in Western Australia. It is a long tongued bee, of the tribe Anthophorini and genus ''Amegilla,'' the second largest genus in Anthophorini. The Dawson's burrowing bee is one of the largest Australian bee species, growing to be in length and in wingspan. With the exception of their faces, the bees are covered in brown fur, if male, or brown and white fur if female. They are similar in size and coloring to Australian carpenter bees. They are known solitary nesters. Though each female bee will build her own nest, they aggregate in large communities that give the appearance of colonies. Their nests are dug into the ground, with individual capsules created for each brood cell. Each female will only breed once in their breeding season. The males of the species are dimorphic, based on brood provisioning strategies during development. The larger males ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Voltinism
Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism. * Univoltine (monovoltine) – (adjective) referring to organisms having one brood or generation per year * Bivoltine (divoltine) – (adjective) referring to organisms having two broods or generations per year *Trivoltine – (adjective) referring to organisms having three broods or generations per year * Multivoltine (polyvoltine) – (adjective) referring to organisms having more than two broods or generations per year * Semivoltine – There are two meanings: :* (''biology'') Less than univoltine; having a brood or generation less often than once per year :* or (adjective) referring to organisms whose generation time is more than one year. Examples The speckled wood butterfly is univoltine in the northern part of its range, e.g. nor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. It is distinguished from '' genetic variability'', which describes the tendency of genetic characteristics to vary. Genetic diversity serves as a way for populations to adapt to changing environments. With more variation, it is more likely that some individuals in a population will possess variations of alleles that are suited for the environment. Those individuals are more likely to survive to produce offspring bearing that allele. The population will continue for more generations because of the success of these individuals. The academic field of population genetics includes several hypotheses and theories regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Variance
Genetic variance is a concept outlined by the English biologist and statistician Ronald Fisher in his fundamental theorem of natural selection. In his 1930 book ''The Genetical Theory of Natural Selection'', Fisher postulates that the rate of change of biological fitness can be calculated by the genetic variance of the fitness itself. Fisher tried to give a statistical formula about how the change of fitness in a population can be attributed to changes in the allele frequency. Fisher made no restrictive assumptions in his formula concerning fitness parameters, mate choices or the number of allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...s and loci involved. Definition Phenotypic variance, usually combines the genotype variance with the environmental variance. Geneti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Drift
Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation. It can also cause initially rare alleles to become much more frequent and even fixed. When few copies of an allele exist, the effect of genetic drift is more notable, and when many copies exist, the effect is less notable. In the middle of the 20th century, vigorous debates occurred over the relative importance of natural selection versus neutral processes, including genetic drift. Ronald Fisher, who explained natural selection using Mendelian genetics, held the view that genetic drift plays at most a minor role in evolution, and this remained the dominant view for several decades. In 1968, population geneticist Motoo Kimura rekindled the debate with his neutral theory of molecular evolution, which claims that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Effective Population Size
The effective population size (''N''''e'') is a number that, in some simplified scenarios, corresponds to the number of breeding individuals in the population. More generally, ''N''''e'' is the number of individuals that an idealised population would need to have in order for some specified quantity of interest (typically change of genetic diversity or inbreeding rates) to be the same as in the real population. Idealised populations are based on unrealistic but convenient simplifications such as random mating, simultaneous birth of each new generation, constant population size, and equal numbers of children per parent. For most quantities of interest and most real populations, the effective population size ''N''''e'' is usually smaller than the census population size ''N'' of a real population. The same population may have multiple effective population sizes, for different properties of interest, including for different genetic loci. The effective population size is most commonly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
