Genetically modified tree
A genetically modified tree is a tree whose DNA has been modified using genetic engineering techniques. In most cases the aim is to introduce a novel trait to the plant which does not occur within the species. Examples include resistance to certain pests, environmental conditions, herbicide tolerance, or the alteration of lignin levels in order to reduce pulping costs. Genetically modified forest trees are not yet approved for commercial use, with the exception of insect-resistant poplar trees in China, and one case of GM Eucalyptus in Brazil. Several genetically modified forest tree species are undergoing field trials for deregulation, much of the research is being carried out by the pulp and paper industry with the intention of increasing the productivity of existing tree stock. Certain genetically modified orchard tree species have been deregulated for commercial use in the United States including the papaya and plum; the development and use of GM trees remains at an early stage in comparison to GM crops.
Research into genetically modified trees has been ongoing since 1988. Concerns surrounding the biosafety implications of releasing genetically modified trees into the wild have held back regulatory approval of GM forest trees; this concern is exemplified in the Convention on Biological Diversity's stance: The Conference of the Parties, Recognising the uncertainties related to the potential environmental and socio-economic impacts, including long term and trans-boundary impacts, of genetically modified trees on global forest biological diversity, as well as on the livelihoods of indigenous and local communities, given the absence of reliable data and of capacity in some countries to undertake risk assessments and to evaluate those potential impacts, recommends parties to take a precautionary approach when addressing the issue of genetically modified trees. A precondition for further commercialization of GM forest trees is to be their complete sterility. Plantation trees remain phenotypically similar to their wild cousins in that most are the product of no more than three generations of artificial selection, the risk of transgene escape by pollination with compatible wild species is high.
One of the most credible science-based concerns with GM trees is their potential for wide dispersal of seed and pollen. The fact that pine pollen travels long distances is well established, moving up to 3,000 kilometers from its source. Additionally, many tree species reproduce for a long time before being harvested. In combination these factors have led some to believe that GM trees are worthy of special environmental considerations over GM crops. Ensuring sterility for GM trees has proven elusive. While tree geneticist Steve Strauss predicted that complete containment might be possible by 2020, many questions remain. GM trees under experimental development have been modified with traits intended to provide benefit to industry, foresters or consumers. Due to high regulatory and research costs, the majority of genetically modified trees in silviculture consist of plantation trees, such as eucalyptus and pine. Several companies and organisations in the pulp and paper industry are interested in utilizing GM technology to alter the lignin content of plantation trees.
It is estimated that reducing lignin in plantation trees by genetic modification could reduce pulping costs by up to $15 per cubic metre. Lignin removal from wood fibres conventionally relies on costly and environmentally hazardous chemicals. By developing low-lignin GM trees it is hoped that pulping and bleaching processes will require fewer inputs, mills supplied by low-lignin GM trees may have a reduced impact on their surrounding ecosystems and communities. However, it is argued that reductions in lignin may compromise the structural integrity of the plant, thereby making it more susceptible to wind, snow and disease, which could necessitate pesticide use exceeding that on traditional plantations; this has proven correct, an alternative approach followed by the University of Columbia was developed. This approach was to introduce chemically labile linkages instead, which allows the lignin to break down much more easy. Due to this new approach, the lignin from the trees not only breaks apart when treated with a mild base at temperatures of 100 degrees C, but the trees maintained their growth potential and strength.
Genetic modification can allow trees to cope with abiotic stresses such that their geographic range is broadened. Freeze-tolerant GM eucalyptus trees for use in southern US plantations are being tested in open air sites with such an objective in mind. ArborGen, a tree biotechnology company and joint venture of pulp and paper firms Rubicon, MeadWestvaco and International Paper is leading this research; until now the cultivation of eucalyptus has only been possible on the southern tip of Florida, freeze-tolerance would extend the cultivation range northwards. Orchard trees require a rootstock with reduced vigour to allow them to remain small. Genetic modification could allow the elimination of the rootstock, by making the tree less vigorous, hence reducing its height when mature. Research is being done into. In Brazil, field trials of fast growing GM eucalyptus are underway, they are set to conclude in 2015-2016 with commercialization to result. FuturaGene, a biotechnology company owned by Suzano, a Brazilian pulp and
The phenotype of an organism is the composite of the organism's observable characteristics or traits, including its morphology or physical form and structure. An organism's phenotype results from two basic factors: the expression of an organism's genetic code, or its genotype, the influence of environmental factors, which may interact, further affecting phenotype; when two or more different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented polymorphism is Labrador Retriever coloring. Richard Dawkins in 1978 and again in his 1982 book The Extended Phenotype suggested that bird nests and other built structures such as caddis fly larvae cases and beaver dams can be considered as "extended phenotypes"; the genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces. The distinction is similar to that proposed by August Weismann, who distinguished between germ plasm and somatic cells.
The genotype-phenotype distinction should not be confused with Francis Crick's central dogma of molecular biology, a statement about the directionality of molecular sequential information flowing from DNA to protein, not the reverse. The term "phenotype" has sometimes been incorrectly used as a shorthand for phenotypic difference from wild type, bringing the absurd statement that a mutation has no phenotype. Despite its straightforward definition, the concept of the phenotype has hidden subtleties, it may seem that anything dependent on the genotype is a phenotype, including molecules such as RNA and proteins. Most molecules and structures coded by the genetic material are not visible in the appearance of an organism, yet they are observable and are thus part of the phenotype, it may seem that this goes beyond the original intentions of the concept with its focus on the organism in itself. Either way, the term phenotype includes inherent traits or characteristics that are observable or traits that can be made visible by some technical procedure.
A notable extension to this idea is the presence of "organic molecules" or metabolites that are generated by organisms from chemical reactions of enzymes. Another extension adds behavior to the phenotype. Behavioral phenotypes include cognitive and behavioral patterns; some behavioral phenotypes may characterize psychiatric syndromes. Phenotypic variation is a fundamental prerequisite for evolution by natural selection, it is the living organism as a whole that contributes to the next generation, so natural selection affects the genetic structure of a population indirectly via the contribution of phenotypes. Without phenotypic variation, there would be no evolution by natural selection; the interaction between genotype and phenotype has been conceptualized by the following relationship: genotype + environment → phenotype A more nuanced version of the relationship is: genotype + environment + genotype & environment interactions → phenotype Genotypes have much flexibility in the modification and expression of phenotypes.
The plant Hieracium umbellatum is found growing in two different habitats in Sweden. One habitat is rocky, sea-side cliffs, where the plants are bushy with broad leaves and expanded inflorescences; these habitats alternate along the coast of Sweden and the habitat that the seeds of Hieracium umbellatum land in, determine the phenotype that grows. An example of random variation in Drosophila flies is the number of ommatidia, which may vary between left and right eyes in a single individual as much as they do between different genotypes overall, or between clones raised in different environments; the concept of phenotype can be extended to variations below the level of the gene that affect an organism's fitness. For example, silent mutations that do not change the corresponding amino acid sequence of a gene may change the frequency of guanine-cytosine base pairs; these base pairs have a higher thermal stability than adenine-thymine, a property that might convey, among organisms living in high-temperature environments, a selective advantage on variants enriched in GC content.
Richard Dawkins described a phenotype that included all effects that a gene has on its surroundings, including other organisms, as an extended phenotype, arguing that "An animal's behavior tends to maximize the survival of the genes'for' that behavior, whether or not those genes happen to be in the body of the particular animal performing it." For instance, an organism such as a beaver modifies its environment by building a beaver dam. When a bird feeds a brood parasite such as a cuckoo, it is unwittingly extending its phenotype.
Marker assisted selection or marker aided selection is an indirect selection process where a trait of interest is selected based on a marker linked to a trait of interest, rather than on the trait itself. This process has been extensively researched and proposed for plant and animal breeding as of 2013 "breeding programs based on DNA markers for improving quantitative traits in plants are rare". For example, using MAS to select individuals with disease resistance involves identifying a marker allele, linked with disease resistance rather than the level of disease resistance; the assumption is that the marker associates at high frequency with the gene or quantitative trait locus of interest, due to genetic linkage. MAS can be useful to select for traits that are difficult or expensive to measure, exhibit low heritability and/or are expressed late in development. At certain points in the breeding process the specimens are examined to ensure that they express the desired trait; the majority of MAS work in the present era uses DNA-based markers.
However, the first markers that allowed indirect selection of a trait of interest were morphological markers. In 1923, Sax first reported association of a inherited genetic marker with a quantitative trait in plants when he observed segregation of seed size associated with segregation for a seed coat color marker in beans. In 1935, Rasmusson demonstrated linkage of flowering time in peas with a inherited gene for flower color. Markers may be: Morphological - These markers are detectable by eye, by simple visual inspection. Examples of this type of marker include the presence or absence of an awn, leaf sheath coloration, grain color, aroma of rice etc. In well-characterized crops like maize, pea, barley or wheat, tens or hundreds of genes that determine morphological traits have been mapped to specific chromosome locations. Biochemical- A protein that can be extracted and observed. Cytological - The chromosomal banding produced by different stains. DNA-based- Including microsatellites, restriction fragment length polymorphism, random amplification of polymorphic DNA, amplified fragment length polymorphism, single nucleotide polymorphisms.
The following terms are less relevant to discussions of MAS in plant and animal breeding, but are relevant in molecular biology research: Positive selectable markers are selectable markers that confer selective advantage to the host organism. An example would be antibiotic resistance, which allows the host organism to survive antibiotic selection. Negative selectable markers are selectable markers that eliminate or inhibit growth of the host organism upon selection. An example would be thymidine kinase. A distinction can be made between screenable markers. Most MAS uses screenable markers rather than selectable markers; the gene of interest directly causes production of protein or RNA that produce a desired trait or phenotype, whereas markers are genetically linked to the gene of interest. The gene of interest and the marker tend to move together during segregation of gametes due to their proximity on the same chromosome and concomitant reduction in recombination between the marker and gene of interest.
For some traits, the gene of interest has been discovered and the presence of desirable alleles can be directly assayed with a high level of confidence. However, if the gene of interest is not known, markers linked to the gene of interest can still be used to select for individuals with desirable alleles of the gene of interest; when markers are used there may be some inaccurate results due to inaccurate tests for the marker. There can be false positive results when markers are used, due to recombination between the marker of interest and gene. A perfect marker would elicit no false positive results; the term'perfect marker' is sometimes used when tests are performed to detect a SNP or other DNA polymorphism in the gene of interest, if that SNP or other polymorphism is the direct cause of the trait of interest. The term'marker' is still appropriate to use when directly assaying the gene of interest, because the test of genotype is an indirect test of the trait or phenotype of interest. An ideal marker: Easy recognition of all possible phenotypes from all different alleles Demonstrates measurable differences in expression between trait types or gene of interest alleles, early in the development of the organism Testing for the marker does not have variable success depending on the allele at the marker locus or the allele at the target locus.
Low or null interaction among the markers allowing the use of many at the same time in a segregating population Abundant in number Polymorphic Morphological markers are associated with several general deficits that reduce their usefulness including: the delay of marker expression until late into the development of t
Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion while the lower part is called the rootstock; the success of this joining requires that the vascular tissue grow together and such joining is called inosculation. The technique is most used in asexual propagation of commercially grown plants for the horticultural and agricultural trades. In most cases, one plant is selected for its roots and this is called the stock or rootstock; the other plant is selected for its stems, flowers, or fruits and is called the scion or cion. The scion contains the desired genes to be duplicated in future production by the stock/scion plant. In stem grafting, a common grafting method, a shoot of a selected, desired plant cultivar is grafted onto the stock of another type. In another common form called bud grafting, a dormant side bud is grafted onto the stem of another stock plant, when it has inosculated it is encouraged to grow by pruning off the stem of the stock plant just above the newly grafted bud.
For successful grafting to take place, the vascular cambium tissues of the stock and scion plants must be placed in contact with each other. Both tissues must be kept alive until the graft has "taken" a period of a few weeks. Successful grafting only requires. Research conducted in Arabidopsis thaliana hypocotyls have shown that the connection of phloem takes place after 3 days of initial grafting, whereas the connection of xylem can take up to 7 days. Joints formed by grafting are not as strong as formed joints, so a physical weak point still occurs at the graft because only the newly formed tissues inosculate with each other; the existing structural tissue of the stock plant does not fuse. Precocity: The ability to induce fruitfulness without the need for completing the juvenile phase. Juvenility is the natural state through which a seedling plant must pass before it can become reproductive. In most fruiting trees, juvenility may last between 5 and 9 years, but in some tropical fruits e.g. Mangosteen, juvenility may be prolonged for up to 15 years.
Grafting of mature scions onto rootstocks can result in fruiting in as little as two years. Dwarfing: To induce dwarfing or cold tolerance or other characteristics to the scion. Most apple trees in modern orchards are grafted on to dwarf or semi-dwarf trees planted at high density, they provide more fruit per unit of land, higher quality fruit, reduce the danger of accidents by harvest crews working on ladders. Care must be taken when planting semi-dwarf trees. If such a tree is planted with the graft below the soil the scion portion can grow roots and the tree will still grow to its standard size. Ease of propagation: Because the scion is difficult to propagate vegetatively by other means, such as by cuttings. In this case, cuttings of an rooted plant are used to provide a rootstock. In some cases, the scion may be propagated, but grafting may still be used because it is commercially the most cost-effective way of raising a particular type of plant. Hybrid breeding: To speed maturity of hybrids in fruit tree breeding programs.
Hybrid seedlings may take ten or more years to fruit on their own roots. Grafting can reduce the time to shorten the breeding program. Hardiness: Because the scion has weak roots or the roots of the stock plants are tolerant of difficult conditions. E.g. many Western Australian plants are sensitive to dieback on heavy soils, common in urban gardens, are grafted onto hardier eastern Australian relatives. Grevilleas and eucalypts are examples. Sturdiness: To provide a strong, tall trunk for certain ornamental shrubs and trees. In these cases, a graft is made at a desired height on a stock plant with a strong stem; this is used to raise'standard' roses, which are rose bushes on a high stem, it is used for some ornamental trees, such as certain weeping cherries. Disease/pest resistance: In areas where soil-borne pests or pathogens would prevent the successful planting of the desired cultivar, the use of pest/disease tolerant rootstocks allow the production from the cultivar that would be otherwise unsuccessful.
A major example is the use of rootstocks in combating Phylloxera. Pollen source: To provide pollenizers. For example, in planted or badly planned apple orchards of a single variety, limbs of crab apple may be grafted at spaced intervals onto trees down rows, say every fourth tree; this takes care of pollen needs at blossom time, yet does not confuse pickers who might otherwise mix varieties while harvesting, as the mature crab apples are so distinct from other apple varieties. Repair: To repair damage to the trunk of a tree that would prohibit nutrient flow, such as stripping of the bark by rodents that girdles the trunk. In this case a bridge graft may be used to connect tissues receiving flow from the roots to tissues above the damage that have been severed from the flow. Where a water sprout, basal shoot or sapling of the same species is growing nearby, any of these can be grafted to the area above the damage by a method called inarch grafting; these alternatives to scions must be of the correct length to span the gap of the wound.
Changing cultivars: To change the cultivar in a fruit orchard to a more profitable cultivar, called top working. It may be faster to graft a new cultivar onto existing limbs of established trees than to replant an entire orchard. Maintain consistency: Apples are notorious for their genetic variability differing in multiple characteristics, such as, size and flavor, of fruits located on the same tree. In the commercia
Backcrossing is a crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity, closer to that of the parent. It is used in animal breeding and in production of gene knockout organisms. Backcrossed hybrids are sometimes described with acronym "BC", for example, an F1 hybrid crossed with one of its parents can be termed a BC1 hybrid, a further cross of the BC1 hybrid to the same parent produces a BC2 hybrid. If the recurrent parent is an elite genotype, at the end of the backcrossing programme an elite genotype is recovered; as there is no "new" recombination, the elite combination is not lost. Works poorly for quantitative traits Is more restricted for recessive traits In practice, sections of genome from the non-recurrent parents are still present and can have unwanted traits associated with them For wide crosses, limited recombination may maintain thousands of ‘alien’ genes within the elite cultivar Many backcrosses are required to produce a new cultivar which can take many years York radiate groundsel is a occurring hybrid species of Oxford ragwort and common groundsel.
It is thought to have arisen from a backcrossing of the F1 hybrid with S. vulgaris. Again, the pure tall and pure dwarf pea plants when crossed in the parental generation, they produce all heterozygote tall pea plants in the first filial generation; the cross between first filial heterozygote tall pea plant and pure tall or pure dwarf pea plant of the parental generation is an example for the back-crossing between two plants. In this case, the filial generation formed after the back cross may have a phenotype ratio of 1:1 if the cross is made with recessive parent or else all offspring may be having phenotype of dominant trait if back cross is with parent having dominant trait; the former of these traits is called a test cross. In plants, inbred backcross lines refers to lines of plants derived from the repeated backcrossing of a line with artificially recombinant DNA with the wild type, operating some kind of selection that can be phenotypical or through a molecular marker. Backcrossing may be deliberately employed in animals to transfer a desirable trait in an animal of inferior genetic background to an animal of preferable genetic background.
In gene knockout experiments in particular, where the knockout is performed on cultured stem cell lines, but is required in an animal with a different genetic background, the knockout animal is backcrossed against the animal of the required genetic background. As the figure shows, each time that the mouse with the desired trait is crossed with a mouse of a constant genetic background, the average percentage of the genetic material of the offspring, derived from that constant background increases; the result, after sufficient reiterations, is an animal with the desired trait in the desired genetic background, with the percentage of genetic material from the original stem cells reduced to a minimum. Due to the nature of meiosis, in which chromosomes derived from each parent are randomly shuffled and assigned to each nascent gamete, the percentage of genetic material deriving from either cell-line will vary between offspring of a single crossing but will have an expected value; the genotype of each member of offspring may be assessed to choose not only an individual that carries the desired genetic trait, but the minimum percentage of genetic material from the original stem cell line.
A consomic strain is an inbred strain with one of its chromosomes replaced by the homologous chromosome of another inbred strain via a series of marker-assisted backcrosses. Introgression The Plant Breeding and Genomics Community of Practice on eXtension - education and training materials for plant breeders and allied professionals
Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are related genetically. By analogy, the term is used in human reproduction, but more refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity. Inbreeding results in homozygosity, which can increase the chances of offspring being affected by deleterious or recessive traits; this leads to at least temporarily decreased biological fitness of a population, its ability to survive and reproduce. An individual who inherits such deleterious traits is colloquially referred to as inbred; the avoidance of expression of such deleterious recessive alleles caused by inbreeding, via inbreeding avoidance mechanisms, is the main selective reason for outcrossing. Crossbreeding between populations often has positive effects on fitness-related traits, but sometimes leads to negative effects known as outbreeding depression.
However increased homozygosity increases probability of fixing beneficial alleles and slightly decreases probability of fixing deleterious alleles in population. Inbreeding can result in purging of deleterious alleles from a population through purifying selection. Inbreeding is a technique used in selective breeding. For example, in livestock breeding, breeders may use inbreeding when trying to establish a new and desirable trait in the stock and for producing distinct families within a breed, but will need to watch for undesirable characteristics in offspring, which can be eliminated through further selective breeding or culling. Inbreeding helps to ascertain the type of gene action affecting a trait. Inbreeding is used to reveal deleterious recessive alleles, which can be eliminated through assortative breeding or through culling. In plant breeding, inbred lines are used as stocks for the creation of hybrid lines to make use of the effects of heterosis. Inbreeding in plants occurs in the form of self-pollination.
Inbreeding can influence gene expression which can prevent inbreeding depression. Offspring of biologically related persons are subject to the possible effects of inbreeding, such as congenital birth defects; the chances of such disorders are increased when the biological parents are more related. This is because such pairings have a 25% probability of producing homozygous zygotes, resulting in offspring with two recessive alleles, which can produce disorders when these alleles are deleterious; because most recessive alleles are rare in populations, it is unlikely that two unrelated marriage partners will both be carriers of the same deleterious allele. It should be noted that for each homozygous recessive individual formed there is an equal chance of producing a homozygous dominant individual — one devoid of the harmful allele. Contrary to common belief, inbreeding does not in itself alter allele frequencies, but rather increases the relative proportion of homozygotes to heterozygotes. In the short term, incestuous reproduction is expected to increase the number of spontaneous abortions of zygotes, perinatal deaths, postnatal offspring with birth defects.
The advantages of inbreeding may be the result of a tendency to preserve the structures of alleles interacting at different loci that have been adapted together by a common selective history. Malformations or harmful traits can stay within a population due to a high homozygosity rate, this will cause a population to become fixed for certain traits, like having too many bones in an area, like the vertebral column of wolves on Isle Royale or having cranial abnormalities, such as in Northern elephant seals, where their cranial bone length in the lower mandibular tooth row has changed. Having a high homozygosity rate is problematic for a population because it will unmask recessive deleterious alleles generated by mutations, reduce heterozygote advantage, it is detrimental to the survival of small, endangered animal populations; when deleterious recessive alleles are unmasked due to the increased homozygosity generated by inbreeding, this can cause inbreeding depression. There may be other deleterious effects besides those caused by recessive diseases.
Thus, similar immune systems may be more vulnerable to infectious diseases. Inbreeding history of the population should be considered when discussing the variation in the severity of inbreeding depression between and within species. With persistent inbreeding, there is evidence that shows that inbreeding depression becomes less severe; this is associated with the unmasking and elimination of deleterious recessive alleles. However, inbreeding depression is not a temporary phenomenon because this elimination of deleterious recessive alleles will never be complete. Eliminating deleterious mutations through inbreeding under moderate selection is not as effective. Fixation of alleles most occurs through Muller's ratchet, when an asexual population's genome accumulates deleterious mutations that are irreversible. Despite all its disadvantages, inbreeding can have a variety of advantages, such as reducing the recombination load, allowing the expression of recessive advantageous phenotypes, it has been proposed th
Purebreds called purebreeds, are cultivated varieties or cultivars of an animal species, achieved through the process of selective breeding. When the lineage of a purebred animal is recorded, that animal is said to be pedigreed; the term purebred is confused with the proper noun Thoroughbred, which refers to a specific breed of horse, one of the first breeds for which a written national stud book was created since the 18th century. Thus a purebred animal should never be called a "thoroughbred" unless the animal is a registered Thoroughbred horse. In the world of selective animal breeding, to "breed true" means that specimens of an animal breed will breed true-to-type when mated like-to-like. A puppy from two purebred dogs of the same breed, for example, will exhibit the traits of its parents, not the traits of all breeds in the subject breed's ancestry. However, breeding from too small a gene pool direct inbreeding, can lead to the passing on of undesirable characteristics or a collapse of a breed population due to inbreeding depression.
Therefore, there is a question, heated controversy, as to when or if a breed may need to allow "outside" stock in for the purpose of improving the overall health and vigor of the breed. Because pure-breeding creates a limited gene pool, purebred animal breeds are susceptible to a wide range of congenital health problems; this problem is prevalent in competitive dog breeding and dog show circles due to the singular emphasis on aesthetics rather than health or function. Such problems occur within certain segments of the horse industry for similar reasons; the problem is further compounded. The opposite effect to that of the restricted gene pool caused by pure-breeding is known as hybrid vigor, which results in healthier animals. A pedigreed animal is one; this is tracked by a major registry. The number of generations required varies from breed to breed, but all pedigreed animals have papers from the registering body that attest to their ancestry; the word "pedigree" appeared in the English language in 1410 as "pee de Grewe", "pedegrewe" or "pedegru", each of those words being borrowed to the Middle French "pié de grue", meaning "crane foot".
This comes from a visual analogy between the trace of the bird's foot and the three lines used in the English official registers to show the ramifications of a genealogical tree. Sometimes the word purebred is used synonymously with pedigreed, but purebred refers to the animal having a known ancestry, pedigree refers to the written record of breeding. Not all purebred animals have their lineage in written form. For example, until the 20th century, the Bedouin people of the Arabian peninsula only recorded the ancestry of their Arabian horses via an oral tradition, supported by the swearing of religiously based oaths as to the asil or "pure" breeding of the animal. Conversely, some animals may have a recorded pedigree or a registry, but not be considered "purebred". Today the modern Anglo-Arabian horse, a cross of Thoroughbred and Arabian bloodlines, is considered such a case. A purebred dog is a dog of a modern breed of dog, with written documentation showing the individual purebred dog's descent from its breeds' foundation stock.
In dogs, the term breed is used two ways: loosely, to refer to dog landraces of dog. Purebred dogs are breeds in the second sense. New breeds of dog are being created, there are many websites for new breed associations and breed clubs offering legitimate registrations for new or rare breeds; when dogs of a new breed are "visibly similar in most characteristics" and have reliable documented descent from a "known and designated foundation stock" they can be considered members of a breed, and, if an individual dog is documented and registered, it can be called purebred. The domestication of the horse resulted in a small number of domesticated stallions being crossed on wild mares that had adapted to local conditions; this produced horses of four basic body types, once thought to be wild prototypes, but now considered to be landraces. Many of these animals were bred true to original type by selected breeding, though emphasizing certain inherent traits to a greater degree than others. In other cases, horses of different body types were cross bred until a desired characteristic was achieved and bred true.
Written and oral histories of various animals or pedigrees of certain types of horse have been kept throughout history, though breed registry stud books trace only to about the 13th century, at least in Europe, when pedigrees were tracked in writing, the practice of declaring a type of horse to be a breed or a purebred became more widespread. Certain horse breeds, such as the Andalusian horse and the Arabian horse, are claimed by aficionados of the respective breeds to be ancient, near-pure descendants from an ancient wild prototype, though mapping of the horse genome as well as the mtDNA and y-DNA of various breeds has disproved such claims. A cat whose ancestry is formally registered is called a purebred cat. Technically, a purebred cat is one whose ancestry