The corridor where WWW was born. CERNground floor of building No.
Genetic diversity and Population genetics An individual organism's phenotype results from both its genotype and the influence from the environment it has lived in. A substantial part of the phenotypic variation in a population is caused by genotypic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene.
Variation disappears when a new allele reaches the point of fixation —when it either disappears from the population or replaces the ancestral allele entirely. Before the discovery of Mendelian genetics, one common hypothesis was blending inheritance. But with blending inheritance, genetic variance would be rapidly lost, making evolution by natural selection implausible.
The Hardy—Weinberg principle provides the solution to how variation is maintained in a population with Mendelian inheritance. The frequencies of alleles variations in a gene will remain constant in the absence of selection, mutation, migration and genetic drift.
Despite the constant introduction of new variation through mutation and gene flow, most of the genome of a species is identical in all individuals of that species. Mutation Duplication of part of a chromosome Mutations are changes in the DNA sequence of a cell's genome.
When mutations occur, they may alter the product of a geneor prevent the gene from functioning, or have no effect. This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function.
Sexual reproductionGenetic recombinationand Evolution of sexual reproduction In asexual organisms, genes are inherited together, or linked, as they cannot mix with genes of other organisms during reproduction.
In contrast, the offspring of sexual organisms contain random mixtures of their parents' chromosomes that are produced through independent assortment. In a related process called homologous recombinationsexual organisms exchange DNA between two matching chromosomes.
If each individual were to contribute to the same number of offspring twoa the sexual population remains the same size each generation, where the b Asexual reproduction population doubles in size each generation. The two-fold cost of sex was first described by John Maynard Smith.
This cost does not apply to hermaphroditic species, like most plants and many invertebrates. The Red Queen hypothesis has been used to explain the significance of sexual reproduction as a means to enable continual evolution and adaptation in response to coevolution with other species in an ever-changing environment.
Gene flow Gene flow is the exchange of genes between populations and between species. Gene flow can be caused by the movement of individuals between separate populations of organisms, as might be caused by the movement of mice between inland and coastal populations, or the movement of pollen between heavy-metal-tolerant and heavy-metal-sensitive populations of grasses.
Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer. Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria.
It is possible that eukaryotes themselves originated from horizontal gene transfers between bacteria and archaea. From a neo-Darwinian perspective, evolution occurs when there are changes in the frequencies of alleles within a population of interbreeding organisms,  for example, the allele for black colour in a population of moths becoming more common.
Mechanisms that can lead to changes in allele frequencies include natural selection, genetic drift, genetic hitchhiking, mutation and gene flow. Natural selection Further information: Sexual selection Evolution by means of natural selection is the process by which traits that enhance survival and reproduction become more common in successive generations of a population.
It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts: Different traits confer different rates of survival and reproduction differential fitness.
These traits can be passed from generation to generation heritability of fitness. More offspring are produced than can possibly survive, and these conditions produce competition between organisms for survival and reproduction.
Consequently, organisms with traits that give them an advantage over their competitors are more likely to pass on their traits to the next generation than those with traits that do not confer an advantage. The central concept of natural selection is the evolutionary fitness of an organism.
These traits are said to be "selected for. Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele becoming rarer—they are "selected against. These charts depict the different types of genetic selection. On each graph, the x-axis variable is the type of phenotypic trait and the y-axis variable is the number of organisms.
Group A is the original population and Group B is the population after selection.
Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorised into three different types. The first is directional selectionwhich is a shift in the average value of a trait over time—for example, organisms slowly getting taller.
This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilising selection there is selection against extreme trait values on both ends, which causes a decrease in variance around the average value and less diversity.Science is complex and multi-faceted, but the most important characteristics of science are straightforward: Science focuses exclusively on the natural world, and does not deal with supernatural explanations..
Science is a way of learning about what is in the natural world, how the natural world works, and how the natural world got to be the way it is. The World Wide Web (WWW), also called the Web, is an information space where documents and other web resources are identified by Uniform Resource Locators (URLs), interlinked by hypertext links, and accessible via the Internet.
English scientist Tim Berners-Lee invented the World Wide Web in He wrote the first web browser in while employed at CERN near Geneva, Switzerland. A process like the scientific method that involves such backing up and repeating is called an iterative process. Whether you are doing a science fair project, a classroom science activity, independent research, or any other hands-on science inquiry understanding the steps of the scientific method will help you focus your scientific question and work through your observations and data to answer the .
The Online Writing Lab (OWL) at Purdue University houses writing resources and instructional material, and we provide these as a free service of the Writing Lab at Purdue. The USPTO Patent Application Initiatives Timeline displays various programs and initiatives that are available to applicants during each phase of the application process.
Each program is designed to advance the progress of a patent application and to provide applicant assistance. In computer science, simulations of evolution using evolutionary algorithms and artificial life started in the s and were extended with simulation of artificial selection.
Artificial evolution became a widely recognised optimisation method as a result of the work of Ingo Rechenberg in the s.