Misplaced Pages

#188811

55-564: The Aegidienberger has a short, muscular, and upright neck with a head that is carried proudly. Overall, it has a strong and sturdy build. The Aegidienberger is a cross between two breeds foreign to Germany, the Peruvian Paso and the Icelandic horse. Selection was specifically for the ability to perform the tölt , a fast ambling gait ; horses without this ability are excluded from registration. A breed society or interest group,

110-446: A purebred gene pool to the point of extinction of a given breed of organism. Cats: The many newly developed and recognized breeds of domestic cat are crossbreeds between existing, well-established breeds (sometimes with limited hybridization with some wild species), to either combine selected traits from the foundation stock , or propagate a rare mutation without excessive inbreeding . However, some nascent breeds such as

165-469: A "breed" rather than a crossbreed. There are disadvantages to creating designer crossbreeds, notably the potential that the cross will be of inferior quality or that it will not produce as consistent a result as would breeding purebred animals. For example, the Poodle is a frequent breed used in creation of designer crossbreeds, due to its non-shedding coat, but that trait does not always breed true when it

220-514: A 75/25 cross, or a BC1 or F1b " backcross ." The breeding of two crossbreeds of the same combination of breeds, creating an F2 cross, an animal that is still a 50–50 cross, but it is the second filial generation of the combination. An F2 cross bred to an F2 cross creates an F3 cross. Similarly, an F2 animal bred to an F1 animal creates an F2b backcross. F3 crosses and greater are called "multi-generational" crosses. In dog breeding, three generations of reliable documented breeding can be considered

275-672: A class of non-coding small RNAs which repress the translation of messenger RNAs (mRNAs) or cause degradation of mRNAs. In hybrid plants, most miRNAs have non-additive expression (it might be higher or lower than the levels in the parents). This suggests that the small RNAs are involved in the growth, vigor and adaptation of hybrids. 'Heterosis without hybridity' effects on plant size have been demonstrated in genetically isogenic F1 triploid (autopolyploid) plants, where paternal genome excess F1 triploids display positive heterosis, whereas maternal genome excess F1s display negative heterosis effects. Such findings demonstrate that heterosis effects, with

330-502: A commercial hybrid in a single step, the single-cross hybrids. Single-cross hybrids are made from just two original parent inbreds. They are generally more vigorous and also more uniform than the earlier double-cross hybrids. The process of creating these hybrids often involves detasseling . Temperate maize hybrids are derived from two main heterotic groups: 'Iowa Stiff Stalk Synthetic', and nonstiff stalk. Hybrid rice sees cultivation in many countries, including China, India, Vietnam, and

385-412: A crossbreed though the term "mixed breed" is technically more accurate. Outcrossing is a type of crossbreeding used within a purebred breed to increase the genetic diversity within the breed, particularly when there is a need to avoid inbreeding . In animal breeding, crossbreeds are crosses within a single species, while hybrids are crosses between different species. In plant breeding terminology,

440-401: A detailed study of purebred Cocker Spaniels, purebred Basenjis, and hybrids between them. They found that hybrids ran faster than either parent, perhaps due to heterosis. Other characteristics, such as basal heart rate, did not show any heterosis—the dog's basal heart rate was close to the average of its parents—perhaps due to the additive effects of multiple genes. Sometimes people working on

495-669: A dog-breeding program find no useful heterosis. All this said, studies do not provide definitive proof of hybrid vigor in dogs. This is largely due to the unknown heritage of most mixed breed dogs used. Results vary wildly, with some studies showing benefit and others finding the mixed breed dogs to be more prone to genetic conditions. In 2014, a study undertaken by the Centre for Integrative Ecology at Deakin University in Geelong, Victoria, concluded that intraspecific hybrids between

550-405: A generation having traits of both parents. Sheep: The large number of breeds of sheep, which vary greatly, creates an opportunity for crossbreeding to be used to tailor production of lambs to the goal of the individual stockman. Llamas: Results of crossbreeding classic and woolly breeds of llama are unpredictable. The resulting offspring displays physical characteristics of either parent, or

605-523: A genome dosage-dependent epigenetic basis, can be generated in F1 offspring that are genetically isogenic (i.e. harbour no heterozygosity). It has been shown that hybrid vigor in an allopolyploid hybrid of two Arabidopsis species was due to epigenetic control in the upstream regions of two genes, which caused major downstream alteration in chlorophyll and starch accumulation. The mechanism involves acetylation or methylation of specific amino acids in histone H3 ,

SECTION 10

#1732782631189

660-435: A hybrid inherits traits from its parents that are not fully compatible, fitness can be reduced. This is a form of outbreeding depression , the effects of which are similar to inbreeding depression. Since the early 1900s, two competing genetic hypotheses, not necessarily mutually exclusive, have been developed to explain hybrid vigor. More recently, an epigenetic component of hybrid vigor has also been established. When

715-543: A large scale for use by farmers. Donald F. Jones at the Connecticut Agricultural Experiment Station , New Haven invented the first practical method of producing a high-yielding hybrid maize in 1914–1917. Jones' method produced a double-cross hybrid, which requires two crossing steps working from four distinct original inbred lines. Later work by corn breeders produced inbred lines with sufficient vigor for practical production of

770-417: A maintainer line, and a restorer line. The second generation was widely adopted in the 1990s. Instead of a CMS line, it uses an environment-sensitive genic male sterile line (EGMS), which can have its sterility reversed based on light or temperature. This removes the need for a maintainer, making the hybridization and breeding process more efficient (albeit still high-maintenance). Second generation lines show

825-508: A mix of characteristics from both, periodically producing a fleeced llama. The results are increasingly unpredictable when both parents are crossbreeds, with possibility of the offspring displaying characteristics of a grandparent, not obvious in either parent. Dogs: A crossbred dog is a cross between two (sometimes more) known breeds, and is usually distinguished from a mixed-breed dog , which has ancestry from many sources, some of which may not be known. Crossbreeds are popular, due to

880-455: A more psychoactive cannabis . Nearly all field corn ( maize ) grown in most developed nations exhibits heterosis. Modern corn hybrids substantially outyield conventional cultivars and respond better to fertilizer . Corn heterosis was famously demonstrated in the early 20th century by George H. Shull and Edward M. East after hybrid corn was invented by Dr. William James Beal of Michigan State University based on work begun in 1879 at

935-465: A mutt or a mongrel , its entire pedigree is known to descend from specific known animals. While the term is best known when applied to certain dog crossbreeds , other animals such as cattle, horses, birds and cats may also be bred in this fashion. Some crossbred breeders start a freestanding breed registry to record designer crossbreds, other crossbreds may be included in an "appendix" to an existing purebred registry. either form of registration may be

990-531: A population is small or inbred, it tends to lose genetic diversity. Inbreeding depression is the loss of fitness due to loss of genetic diversity. Inbred strains tend to be homozygous for recessive alleles that are mildly harmful (or produce a trait that is undesirable from the standpoint of the breeder). Heterosis or hybrid vigor, on the other hand, is the tendency of outbred strains to exceed both inbred parents in fitness. Selective breeding of plants and animals, including hybridization, began long before there

1045-432: A protein closely associated with DNA, which can either activate or repress associated genes. One example of where particular genes may be important in vertebrate animals for heterosis is the major histocompatibility complex (MHC). Vertebrates inherit several copies of both MHC class I and MHC class II from each parent, which are used in antigen presentation as part of the adaptive immune system. Each different copy of

1100-500: A true-breeding population and have a closed stud book . Other types of recognized crossbreeding include that within the American Quarter Horse , which will register horses with one Thoroughbred parent and one registered Quarter Horse parent in the "Appendix" registry, and allow such animals full breed registration status as Quarter Horses if they meet a certain performance standard. Another well-known crossbred horse

1155-420: A yak and an American bison ). The Incas recognized that hybrids of Lama glama (llama) and Vicugna pacos (alpaca) resulted in a hybrid with none of the advantages of either parent. At one time it was thought that dogs and wolves were separate species, and the crosses between dogs and wolves were called wolf hybrids. Today wolves and dogs are both recognized as Canis lupus , but the old term "wolf hybrid"

SECTION 20

#1732782631189

1210-450: A yield increase of 5-10% over first generation lines. The third and current generation uses a nuclear male sterile line (NMS). Third generation lines have a recessive sterility gene, and their cultivation is more lenient towards maintainer lines and environmental conditions. Additionally, transgenes are only present in the maintainer, so hybrid plants can benefit from hybrid vigor without requiring special oversight. The concept of heterosis

1265-399: Is a self-pollinating species, it requires the use of male-sterile lines to generate hybrids from separate lineages. The most common way of achieving this is using lines with genetic male-sterility, as manual emasculation is not optimal for large-scale hybridization. The first generation of hybrid rice was developed in the 1970s. It relies on three lines: a cytoplasmic male sterile (CMS) line,

1320-870: Is also applied in the production of commercial livestock . In cattle, crosses between Black Angus and Hereford produce a cross known as a " Black Baldy ". In swine , "blue butts" are produced by the cross of Hampshire and Yorkshire. Other, more exotic hybrids (two different species, so genetically more dissimilar), such as " beefalo " which are hybrids of cattle and bison, are also used for specialty markets. Within poultry , sex-linked genes have been used to create hybrids in which males and females can be sorted at one day old by color. Specific genes used for this are genes for barring and wing feather growth. Crosses of this sort create what are sold as Black Sex-links, Red Sex-links, and various other crosses that are known by trade names. Commercial broilers are produced by crossing different strains of White Rocks and White Cornish,

1375-431: Is often called a "moggie". A horse of unknown bloodlines is called a grade horse . A designer crossbreed or designer breed is a crossbred animal with purebred parents, usually registered with a breed registry , but from two different breeds . These animals are the result of a deliberate decision to create a specific crossbred animal. Less often, the animal may have more than two pure breeds in its ancestry, but unlike

1430-445: Is part of a designer cross. Also, because breeders of crossbred animals may be less careful about genetic testing and weeding out undesirable traits, certain deleterious dominant genes may still be passed on to a crossbreed offspring. In an F2 cross, recessive genetic traits may also return if the parent animals were both carriers of an undesired trait. Hybrid vigor Heterosis , hybrid vigor , or outbreeding enhancement

1485-423: Is still used. A mixed-breed animal is defined as having undocumented or unknown parentage, while a crossbreed generally has known, usually purebred parents of two distinct breeds or varieties. A dog of unknown parentage is often called a mixed-breed dog, "mutt" or " mongrel ." A cat of unknown parentage is often referred to as a domestic short-haired or domestic long-haired cat generically, and in some dialects

1540-479: Is the Anglo-Arabian , which may be produced by a purebred Arabian horse crossed on a Thoroughbred, or by various crosses of Anglo-Arabians with other Anglo-Arabians, as long as the ensuing animal never has more than 75% or less than 25% of each breed represented in its pedigree. A hybrid animal is one with parentage of two separate species, differentiating it from crossbred animals, which have parentage of

1595-525: Is the improved or increased function of any biological quality in a hybrid offspring. An offspring is heterotic if its traits are enhanced as a result of mixing the genetic contributions of its parents. The heterotic offspring often has traits that are more than the simple addition of the parents' traits, and can be explained by Mendelian or non-Mendelian inheritance . Typical heterotic/hybrid traits of interest in agriculture are higher yield, quicker maturity, stability, drought tolerance etc. In proposing

1650-412: Is the main cause for the fitness advantages of heterosis, then there should be an over-expression of certain genes in the heterozygous offspring compared to the homozygous parents. On the other hand, if dominance is the cause, fewer genes should be under-expressed in the heterozygous offspring compared to the parents. Furthermore, for any given gene, the expression should be comparable to the one observed in

1705-455: The Aegean cat are developed entirely from a local landrace population. Most experimental cat breeds are crossbreeds. Cattle: In cattle, there are systems of crossbreeding. In many crossbreeds, one animal is larger than the other. One is used when the purebred females are particularly adapted to a specific environment, and are crossed with purebred bulls from another environment to produce

Aegidienberger - Misplaced Pages Continue

1760-635: The Flynn effect , the steady rise in IQ test scores around the world during the 20th century, though a review of nine studies found that there is no evidence to suggest inbreeding has an effect on IQ. The term heterosis often causes confusion and even controversy, particularly in selective breeding of domestic animals , because it is sometimes (incorrectly) claimed that all crossbred plants and animals are "genetically superior" to their parents, due to heterosis, . but two problems exist with this claim: An example of

1815-490: The Interessengemeinschaft und Förderverein für Aegidienbergerpferde , was formed in 1994. In the twenty-four years from 1997 to 2020, numbers reported for the breed have never exceeded 60; in 2020 the breeding population was reported to be 29, consisting of 23 mares and 6 stallions. Its conservation status is critical. The Aegidienberger was bred to be a comfortable riding horse with the tölt gait of

1870-421: The warmblood breeds used in the sport horse disciplines, usually registered in an open stud book by a studbook selection procedure that evaluates conformation, pedigree and, in some animals, a training or performance standard. Most warmblood breeds began as a cross of draft horse breeds on Thoroughbreds , but have, in some cases, developed over the past century to the point where they are considered to be

1925-638: The 1980s, as experimental evidence has mounted, the dominance theory has made a comeback. Crow wrote: The current view ... is that the dominance hypothesis is the major explanation of inbreeding decline and [of] the high yield of hybrids. There is little statistical evidence for contributions from overdominance and epistasis . But whether the best hybrids are getting an extra boost from overdominance or favorable epistatic contributions remains an open question. An epigenetic contribution to heterosis has been established in plants, and it has also been reported in animals. MicroRNAs (miRNAs), discovered in 1993, are

1980-678: The Cornish providing a large frame and the Rocks providing the fast rate of gain. The hybrid vigor produced allows the production of uniform birds at a marketable carcass weight at 6–9 weeks of age. Likewise, hybrids between different strains of White Leghorn are used to produce laying flocks that provide the majority of white eggs for sale in the United States. In 2013, a study found that mixed breeds live on average 1.2 years longer than pure breeds. John Scott and John L. Fuller performed

2035-477: The Icelandic, but rather larger and with better adaptation to warmer climates. This equine-related article is a stub . You can help Misplaced Pages by expanding it . Cross-breed A crossbreed is an organism with purebred parents of two different breeds, varieties, or populations. A domestic animal of unknown ancestry, where the breed status of only one parent or grandparent is known, may also be called

2090-571: The Philippines. Compared to inbred lines, hybrids produce approximately 20% greater yield, and comprise 45% of rice planting area in China. Rice production has seen enormous rise in China due to heavy uses of hybrid rice. In China, efforts have generated a super hybrid rice strain ('LYP9') with a production capability around 15 tons per hectare. In India also, several varieties have shown high vigor, including 'RH-10' and 'Suruchi 5401'. Since rice

2145-417: The ambiguous value judgements imposed on hybrids and hybrid vigor is the mule . While mules are almost always infertile, they are valued for a combination of hardiness and temperament that is different from either of their horse or donkey parents. While these qualities may make them "superior" for particular uses by humans, the infertility issue implies that these animals would most likely become extinct without

2200-451: The belief that they have increased vigor without loss of attractiveness of the dog. Certain planned crossbreeding between purebred dogs of different breeds are now widely known as "designer dogs" and can produce puppies worth more than their purebred parents, due to a high demand. Horses: Crossbreeding horses is often done with the intent of ultimately creating a new breed of horse. One type of modern crossbreeding in horses created many of

2255-584: The cause, though, of autoimmune diseases. Crosses between inbreds from different heterotic groups result in vigorous F1 hybrids with significantly more heterosis than F1 hybrids from inbreds within the same heterotic group or pattern. Heterotic groups are created by plant breeders to classify inbred lines, and can be progressively improved by reciprocal recurrent selection. Heterosis is used to increase yields, uniformity, and vigor. Hybrid breeding methods are used in maize , sorghum , rice , sugar beet , onion , spinach , sunflowers , broccoli and to create

Aegidienberger - Misplaced Pages Continue

2310-503: The chance that any particular pathogen will be recognised, and means that more antigenic proteins on any pathogen are likely to be recognised, giving a greater range of T-cell activation, so a greater response. This also means that the immunity acquired to the pathogen is against a greater range of antigens, meaning that the pathogen must mutate more before immunity is lost. Thus, hybrids are less likely to succumb to pathogenic disease and are more capable of fighting off infection. This may be

2365-628: The field of genetics . Population geneticist James Crow (1916–2012) believed, in his younger days, that overdominance was a major contributor to hybrid vigor. In 1998 he published a retrospective review of the developing science. According to Crow, the demonstration of several cases of heterozygote advantage in Drosophila and other organisms first caused great enthusiasm for the overdominance theory among scientists studying plant hybridization. But overdominance implies that yields on an inbred strain should decrease as inbred strains are selected for

2420-419: The first step in recording and tracking pedigrees in order to develop a new breed. The purpose of creating designer crossbreds is usually one or more of the following reasons: Breeders of designer crossbreds borrow the technical language from hybrid plant breeding: A first generation, 50–50 crossbred is an F1 cross . Subsequent generations may see a purebred animal crossed back on a crossbred, creating

2475-416: The fitter of the two parents. In any case, outcross matings provide the benefit of masking deleterious recessive alleles in progeny. This benefit has been proposed to be a major factor in the maintenance of sexual reproduction among eukaryotes, as summarized in the article Evolution of sexual reproduction . Which of the two mechanisms are the "main" reason for heterosis has been a scientific controversy in

2530-438: The genes is able to bind and present a different set of potential peptides to T-lymphocytes . These genes are highly polymorphic throughout populations, but are more similar in smaller, more closely related populations. Breeding between more genetically distant individuals decreases the chance of inheriting two alleles that are the same or similar, allowing a more diverse range of peptides to be presented. This, therefore, increases

2585-443: The performance of their hybrid crosses, as the proportion of harmful recessives in the inbred population rises. Over the years, experimentation in plant genetics has proven that the reverse occurs, that yields increase in both the inbred strains and the hybrids, suggesting that dominance alone may be adequate to explain the superior yield of hybrids. Only a few conclusive cases of overdominance have been reported in all of genetics. Since

2640-404: The same species. Hybrids are usually, but not always, sterile. One of the most ancient types of hybrid animal is the mule , a cross between a female horse and a male donkey . The liger is a hybrid cross between a male lion and female tiger . The yattle is a cross between a cow and a yak . Other crosses include the tigon (between a male tiger and female lion) and yakalo (between

2695-405: The subspecies Platycercus elegans flaveolus and P. e. elegans of the crimson rosella ( P. elegans ) were more likely to fight off diseases than their pure counterparts. Human beings are all extremely genetically similar to one another. Michael Mingroni has proposed heterosis, in the form of hybrid vigor associated with historical reductions of the levels of inbreeding, as an explanation of

2750-418: The term crossbreed is uncommon, and no universal term is used to distinguish hybridization or crossing within a population from those between populations, or even those between species. Crossbreeding is the process of breeding such an organism. It can be beneficially used to maintain health and viability of organisms. However, irresponsible crossbreeding can also produce organisms of inferior quality or dilute

2805-466: The term heterosis to replace the older term heterozygosis , G.H. Shull aimed to avoid limiting the term to the effects that can be explained by heterozygosity in Mendelian inheritance. The physiological vigor of an organism as manifested in its rapidity of growth, its height and general robustness, is positively correlated with the degree of dissimilarity in the gametes by whose union the organism

SECTION 50

#1732782631189

2860-489: The urging of Charles Darwin . Dr. Beal's work led to the first published account of a field experiment demonstrating hybrid vigor in corn, by Eugene Davenport and Perry Holden , 1881. These various pioneers of botany and related fields showed that crosses of inbred lines made from a Southern dent and a Northern flint, respectively, showed substantial heterosis and outyielded conventional cultivars of that era. However, at that time such hybrids could not be economically made on

2915-579: The word 'heterosis' be adopted. Heterosis is often discussed as the opposite of inbreeding depression , although differences in these two concepts can be seen in evolutionary considerations such as the role of genetic variation or the effects of genetic drift in small populations on these concepts. Inbreeding depression occurs when related parents have children with traits that negatively influence their fitness largely due to homozygosity . In such instances, outcrossing should result in heterosis. Not all outcrosses result in heterosis. For example, when

2970-423: Was an understanding of underlying scientific principles. In the early 20th century, after Mendel's laws came to be understood and accepted, geneticists undertook to explain the superior vigor of many plant hybrids. Two competing hypotheses, which are not mutually exclusive, were developed: Dominance and overdominance have different consequences for the gene expression profile of the individuals. If overdominance

3025-467: Was formed … The more numerous the differences between the uniting gametes — at least within certain limits — the greater on the whole is the amount of stimulation … These differences need not be Mendelian in their inheritance … To avoid the implication that all the genotypic differences which stimulate cell-division, growth and other physiological activities of an organism are Mendelian in their inheritance and also to gain brevity of expression I suggest … that

#188811