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Selection Limits
A selection limit is a term from animal breeding and quantitative genetics that refers to a cessation of progress even when continued directional selection is being applied to a trait, such as body size. In other words, a breeder or scientist is using selective breeding (artificial selection) and choosing individuals as breeders within a population based on some phenotypic trait or traits. If this is done, then the average value of the population typically evolves across generations in the direction being favored by selection (i.e., for higher or lower values of the trait), but then at some point the population stops evolving. The trait under selection is then said to have reached a limit or plateau at that value. Details The existence of limits in artificial selection experiments was discussed in the scientific literature in the 1940s or earlier. The most obvious possible cause of reaching a limit (or plateau) when a population is under continued directional selection is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selection Limits 1
Selection may refer to: Science * Selection (biology), also called natural selection, selection in evolution ** Sex selection, in genetics ** Mate selection, in mating ** Sexual selection in humans, in human sexuality ** Human mating strategies, in human sexuality * Social selection, within social groups * Selection (linguistics), the ability of predicates to determine the semantic content of their arguments * Selective school, Selection in schools, the admission of students on the basis of selective criteria * Selection effect, a distortion of data arising from the way that the data are collected * A selection, or choice function, a function that selects an element from a set Religion * Divine election, Divine selection, selection by God * Papal selection, selection by clergy Computing * Selection (user interface) ** X Window selection * Selection (evolutionary algorithm) * Selection (relational algebra) * Selection-based search, a search engine system in which the user i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fitness (biology)
Fitness (often denoted w or ω in population genetics models) is a quantitative representation of individual reproductive success. It is also equal to the average contribution to the gene pool of the next generation, made by the same individuals of the specified genotype or phenotype. Fitness can be defined either with respect to a genotype or to a phenotype in a given environment or time. The fitness of a genotype is manifested through its phenotype, which is also affected by the developmental environment. The fitness of a given phenotype can also be different in different selective environments. With asexual reproduction, it is sufficient to assign fitnesses to genotypes. With sexual reproduction, recombination scrambles alleles into different genotypes every generation; in this case, fitness values can be assigned to alleles by averaging over possible genetic backgrounds. Natural selection tends to make alleles with higher fitness more common over time, resulting in Darwini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Litter (zoology)
A litter is the live birth of multiple offspring at one time in animals from the same mother and usually from one set of parents, particularly from three to eight offspring. The word is most often used for the offspring of mammals, but can be used for any animal that gives birth to multiple young. In comparison, a group of egg (biology), eggs and the offspring that hatch from them are frequently called a clutch (animal), clutch, while young birds are often called a offspring, brood. Animals from the same litter are referred to as littermates. Litter size (typical count) In most female mammals the average litter size is about half the number of mammae. Presumably this enables females to successfully nurse litters even if some mammae fail to produce milk. Naked mole-rats break this "one-half rule" – field caught and lab born litters averaged 11 to 12 pups, and numbers of mammae on wild and captive females were similarly 11 to 12. Maximum litter sizes were 28 in the field and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laboratory Rats
Laboratory rats or lab rats are strain (biology), strains of the rat subspecies ''Rattus norvegicus domestica'' (Domestic Norwegian rat) which are bred and kept for scientific research. While Animal testing on rodents, less commonly used for research than laboratory mice, rats have served as an important animal model for research in psychology and biomedical science, and "lab rat" is commonly used as an idiom for a test subject. Origins of rat breeding In 18th-century Europe, wild brown rats (''Rattus norvegicus'') ran rampant and this infestation fueled the industry of rat-catching. Rat-catchers would not only make money by trapping the rodents, but also by selling them rat meat, for food or, more commonly, for rat-baiting. Rat-baiting was a popular sport, which involved filling a pit with rats and timing how long it took for a terrier to kill them all. Over time, breeding the rats for these contests may have produced color variations, notably the albino rat, albino and hoode ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drosophila
''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit. They should not be confused with the Tephritidae, a related family, which are also called fruit flies (sometimes referred to as "true fruit flies"); tephritids feed primarily on unripe or ripe fruit, with many species being regarded as destructive agricultural pests, especially the Mediterranean fruit fly. One species of ''Drosophila'' in particular, ''Drosophila melanogaster'', has been heavily used in research in genetics and is a common model organism in developmental biology. The terms "fruit fly" and "''Drosophila''" are often used synonymously with ''D. melanogaster'' in modern biological literatur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corn Kernel
Corn kernels are the fruits of Maize, corn (called maize in many countries). Maize is a grain, and the kernels are used in cooking as a vegetable or a source of starch. The kernel comprise endosperm, Germ (grain), germ, pericarp, and tip cap. Description Corn kernels are the fruits of maize. Maize is a grain, and the kernels are used in cooking as a vegetable or a source of starch. The kernels can be of various colors: blackish, blue corn, bluish-gray, purple, green, red, white and yellow. The kernel of maize consists of a pericarp (fruit wall) fused to the seed coat. This type of fruit is typical of the Poaceae, grasses and is called a caryopsis. Maize kernels are frequently and incorrectly referred to as seeds. The kernels are about the size of peas, and adhere in regular rows round a white, pithy substance, which forms the ear. Typical shapes of corn kernels include horse-tooth shape, sphereical cone shape, and spherical shape. Endosperm About 82 percent of the corn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maize
Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native Americans planted it alongside beans and squashes in the Three Sisters polyculture. The leafy stalk of the plant gives rise to male inflorescences or tassels which produce pollen, and female inflorescences called ears. The ears yield grain, known as kernels or seeds. In modern commercial varieties, these are usually yellow or white; other varieties can be of many colors. Maize relies on humans for its propagation. Since the Columbian exchange, it has become a staple food in many parts of the world, with the total production of maize surpassing that of wheat and rice. Much maize is used for animal feed, whether as grain or as the whole plant, which can either be baled or made into the more palatable silage. Sugar-rich varieties called sw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nest
A nest is a structure built for certain animals to hold Egg (biology), eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic material such as twigs, grass, and leaves, or may be a simple depression in the ground, or a hole in a rock, tree, or building. Human-made materials, such as string, plastic, cloth, or paper, may also be used. Nests can be found in all types of habitat. Nest building is driven by a biological urge known as the nesting instinct in birds and mammals. Generally each species has a distinctive style of nest. Nest complexity is roughly correlated with the level of parental care by adults. Nest building is considered a key adaptive advantage among birds, and they exhibit the most variation in their nests ranging from simple holes in the ground to elaborate communal nests hosting hundreds of individuals. Nests of prairie dogs and severa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Season
A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's axial tilt, tilted orbit around the Sun. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to Migration (ecology), migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are a number of both modern and historical definitions of the seasons. The Northern Hemisphere experiences most direct sunlight during May, June, and July (thus the traditional celebration of Midsummer in June), as the hemisphere faces the Sun. For the Southern Hemisphere it is instead in November, December, and January. It is Earth's axial tilt that causes the Sun to be higher in the sky during the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and non-coding genes. During gene expression (the synthesis of Gene product, RNA or protein from a gene), DNA is first transcription (biology), copied into RNA. RNA can be non-coding RNA, directly functional or be the intermediate protein biosynthesis, template for the synthesis of a protein. The transmission of genes to an organism's offspring, is the basis of the inheritance of phenotypic traits from one generation to the next. These genes make up different DNA sequences, together called a genotype, that is specific to every given individual, within the gene pool of the population (biology), population of a given species. The genotype, along with environmental and developmental factors, ultimately determines the phenotype ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenotype
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological properties, and its behavior. An organism's phenotype results from two basic factors: the expression of an organism's genetic code (its genotype) and the influence of environmental factors. Both factors may interact, further affecting the phenotype. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented example of polymorphism is Labrador Retriever coloring; while the coat color depends on many genes, it is clearly seen in the environment as yellow, black, and brown. Richard Dawkins in 1978 and again in his 1982 book '' The Extended Phenotype'' suggested that one can regard bird nests and other built structures such as caddisfly larva cases and beaver dams ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heritability
Heritability is a statistic used in the fields of Animal husbandry, breeding and genetics that estimates the degree of ''variation'' in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is ''not'' explained by the environment or random chance?" Other causes of measured variation in a trait are characterized as environment (biophysical), environmental factors, including observational error. In human studies of heritability these are often apportioned into factors from "shared environment" and "non-shared environment" based on whether they tend to result in persons brought up in the same household being more or less similar to persons who were not. Heritability is estimated by comparing individual phenotypic variation among related individuals in a population, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
