Mutation in the context of "Chromosomal inversion"

Evolutionary biology is a subfield of biology that analyzes the four mechanisms of evolution: natural selection, mutation, genetic drift, and gene flow. The purpose of evolutionary biology is to observe the diversity of life on Earth. The idea of natural selection was first researched by Charles Darwin as he studied bird beaks. The discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology. Huxley was able to take what Charles Darwin discovered and elaborate to build on his understandings.

The investigational range of current research has widened to encompass the genetic architecture of adaptation, molecular evolution, and the different forces that contribute to evolution, such as sexual selection, genetic drift, and biogeography. The newer field of evolutionary developmental biology ("evo-devo") investigates how embryogenesis is controlled, thus yielding a wider synthesis that integrates developmental biology with the fields of study covered by the earlier evolutionary synthesis.

Natural selection is the differential survival and reproduction of individuals due to differences in the relative fitness endowed on them by their own particular complement of observable characteristics. It is a key law or mechanism of evolution which changes the heritable traits characteristic of a population or species over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which is intentional, whereas natural selection is not.

For Darwin natural selection was a law or principle which resulted from three different kinds of process: inheritance, including the transmission of heritable material from parent to offspring and its development (ontogeny) in the offspring; variation, which partly resulted from an organism's own agency (see phenotype; Baldwin effect); and the struggle for existence, which included both competition between organisms and cooperation or 'mutual aid' (particularly in 'social' plants and social animals).

Allopatric speciation (from Ancient Greek ἄλλος (állos) 'other' and πατρίς (patrís) 'fatherland') – also called geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow.

Various geographic changes can arise such as the movement of continents, and the formation of mountains, islands, bodies of water, or glaciers. Human activity such as agriculture or developments can also change the distribution of species populations. These factors can substantially alter a region's geography, resulting in the separation of a species population into isolated subpopulations. The vicariant populations then undergo genetic changes as they become subjected to different selective pressures, experience genetic drift, and accumulate different mutations in the separated populations' gene pools. The barriers prevent the exchange of genetic information between the two populations leading to reproductive isolation. If the two populations come into contact they will be unable to reproduce—effectively speciating. Other isolating factors such as population dispersal leading to emigration can cause speciation (for instance, the dispersal and isolation of a species on an oceanic island) and is considered a special case of allopatric speciation called peripatric speciation.

Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant males and females will sexually reproduce and have offspring together. Domesticated animals are known as breeds, normally bred by a professional breeder, while domesticated plants are known as varieties, cultigens, cultivars, or breeds. Two purebred animals of different breeds produce a crossbreed, and crossbred plants are called hybrids. Flowers, vegetables and fruit-trees may be bred by amateurs and commercial or non-commercial professionals: major crops are usually the provenance of the professionals.

In animal breeding artificial selection is often combined with techniques such as inbreeding, linebreeding, and outcrossing. In plant breeding, similar methods are used. Charles Darwin discussed how selective breeding had been successful in producing change over time in his 1859 book, On the Origin of Species. Its first chapter discusses selective breeding and domestication of such animals as pigeons, cats, cattle, and dogs. Darwin used artificial selection as an analogy to propose and explain the theory of natural selection but distinguished the latter from the former as a separate process that is non-directed.

Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most vertebrates (including humans) have several classes of cones, each sensitive to a different part of the visible spectrum of light. The comparison of the responses of different cone cell classes enables color vision. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration occurring towards the macula and most densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones. Conversely, like rods, they are absent from the optic disc, contributing to the blind spot.

Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer detail and more rapid changes in images because their response times to stimuli are faster than those of rods. In humans, cones are normally one of three types: S-cones, M-cones and L-cones, with each type bearing a different opsin: OPN1SW, OPN1MW, and OPN1LW respectively. These cones are sensitive to visible wavelengths of light that correspond to short-wavelength, medium-wavelength and longer-wavelength light respectively. Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, humans have trichromatic vision. Being color blind can change this, and there have been some verified reports of people with four types of cones, giving them tetrachromatic vision.The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to genetic mutation; different individuals will have cones with different color sensitivity.

Variegation is the appearance of differently coloured zones in the foliage, flowers, and sometimes the stems and fruit of plants, granting a speckled, striped, or patchy appearance. The colors of the patches themselves vary from a slightly lighter shade of the natural coloration to yellow, to white, or other colors entirely such as red and pink. This is caused by varying levels and types of pigment, such as chlorophyll in leaves. Variegation can be caused by genetic mutations affecting pigment production, or by viral infections such as those resulting from mosaic viruses. Many plants are also naturally variegated, such as Goeppertia insignis. Most of these are herbaceous or climbing plants, and are most often species native to tropical rainforests.

Many species which are normally non-variegated are known to display variegation. Their appearance is desirable to enthusiasts, and many such plants are propagated and sold as unique cultivars. However, in individuals where the variegation occurs in normally-photosynthetic cells, the lack of functioning chloroplasts can slow growth rate. Conversely, naturally-variegated plants derive benefits from their appearance, such as improved photosynthetic efficiency in low-light conditions and herbivore deterrence.

Self-replication is any behavior of a dynamical system that yields construction of an identical or similar copy of itself. Biological cells, given suitable environments, reproduce by cell division. During cell division, DNA is replicated and can be transmitted to offspring during reproduction. Biological viruses can replicate, but only by commandeering the reproductive machinery of cells through a process of infection. Harmful prion proteins can replicate by converting normal proteins into rogue forms. Computer viruses reproduce using the hardware and software already present on computers. Self-replication in robotics has been an area of research and a subject of interest in science fiction. Any self-replicating mechanism which does not make a perfect copy (mutation) will experience genetic variation and will create variants of itself. These variants will be subject to natural selection, since some will be better at surviving in their current environment than others and will out-breed them.

In biology, a mechanism is a system of causally interacting parts and processes that produce one or more effects. Phenomena can be explained by describing their mechanisms. For example, natural selection is a mechanism of evolution; other mechanisms of evolution include genetic drift, mutation, and gene flow. In ecology, mechanisms such as predation and host-parasite interactions produce change in ecological systems. In practice, no description of a mechanism is ever complete because not all details of the parts and processes of a mechanism are fully known. For example, natural selection is a mechanism of evolution that includes countless, inter-individual interactions with other individuals, components, and processes of the environment in which natural selection operates.