biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditar ...

, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...

. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigor, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar worki ...

, attention is focused on the numbers of

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...

s. In taxonomy, a key question is how closely related the parent

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

are. Species are reproductively isolated by strong barriers to hybridisation, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

and others after it. Similar barriers exist in plants, with differences in flowering times, pollen vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and the structure of the chromosomes. A few animal species and many plant species, however, are the result of

hybrid speciation Hybrid speciation is a form of speciation where hybridization between two different species leads to a new species, reproductively isolated from the parent species. Previously, reproductive isolation between two species and their parents was tho ...

, including important crop plants such as

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeolog ...

, where the number of chromosomes has been doubled.

Human impact on the environment Human impact on the environment (or anthropogenic impact) refers to changes to biophysical environments and to ecosystems, biodiversity, and natural resources caused directly or indirectly by humans. Modifying the environment to fit the needs ...

has resulted in an increase in the interbreeding between regional species, and the proliferation of

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived the ...

worldwide has also resulted in an increase in hybridisation. This genetic mixing may threaten many species with extinction, while genetic erosion from

monoculture In agriculture, monoculture is the practice of growing one crop species in a field at a time. Monoculture is widely used in intensive farming and in organic farming: both a 1,000-hectare/acre cornfield and a 10-ha/acre field of organic kale a ...

in crop plants may be damaging the gene pools of many species for future breeding. A form of often intentional human-mediated hybridisation is the crossing of wild and domesticated species. This is common in both traditional

horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...

and modern

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peop ...

; many commercially useful fruits, flowers, garden herbs, and trees have been produced by hybridisation. One such flower, '' Oenothera lamarckiana'', was central to early genetics research into mutationism and polyploidy. It is also more occasionally done in the livestock and pet trades; some well-known wild × domestic hybrids are

beefalo Beefalo constitute a hybrid offspring of domestic cattle (''Bos taurus''), usually a male in managed breeding programs, and the American bison (''Bison bison''), usually a female in managed breeding programs. The breed was created to combine the ...

and

wolfdog A wolfdog is a canine produced by the mating of a domestic dog (''Canis familiaris'') with a gray wolf (''Canis lupus''), eastern wolf (''Canis lycaon''), red wolf (''Canis rufus''), or Ethiopian wolf (''Canis simensis'') to produce a h ...

s. Human

selective breeding 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 ma ...

domesticated animals This page gives a list of domesticated animals, also including a list of domestication of animals, animals which are or may be currently undergoing the process of domestication and animals that have an extensive relationship with humans beyond simp ...

and

plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

has resulted in the development of distinct

breeds A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist several slig ...

(usually called

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...

s in reference to plants);

crossbreed A crossbreed is an organism with purebred parents of two different breeds, varieties, or populations. ''Crossbreeding'', sometimes called "designer crossbreeding", is the process of breeding such an organism, While crossbreeding is used to mai ...

s between them (without any wild

stock In finance, stock (also capital stock) consists of all the shares by which ownership of a corporation or company is divided.Longman Business English Dictionary: "stock - ''especially AmE'' one of the shares into which ownership of a company ...

) are sometimes also imprecisely referred to as "hybrids". Hybrid humans existed in prehistory. For example, Neanderthals and anatomically modern humans are thought to have interbred as recently as 40,000 years ago. Mythological hybrids appear in human culture in forms as diverse as the Minotaur, blends of animals, humans and mythical beasts such as

centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as bein ...

s and

sphinx A sphinx ( , grc, σφίγξ , Boeotian: , plural sphinxes or sphinges) is a mythical creature with the head of a human, the body of a lion, and the wings of a falcon. In Greek tradition, the sphinx has the head of a woman, the haunches o ...

es, and the

Nephilim The Nephilim (; ''Nəfīlīm'') are mysterious beings or people in the Hebrew Bible who are large and strong. The word ''Nephilim'' is loosely translated as ''giants'' in some translations of the Hebrew Bible, but left untranslated in others. ...

of the Biblical apocrypha described as the wicked sons of

fallen angel In the Abrahamic religions, fallen angels are angels who were expelled from heaven. The literal term "fallen angel" never appears in any Abrahamic religious texts, but is used to describe angels cast out of heaven"Mehdi Azaiez, Gabriel Said ...

s and attractive women.

Etymology

The term hybrid is derived from Latin ', used for crosses such as of a tame sow and a wild boar. The term came into popular use in English in the 19th century, though examples of its use have been found from the early 17th century. Conspicuous hybrids are popularly named with

portmanteau word A portmanteau word, or portmanteau (, ) is a blend of wordsliger and tigon).

As seen by different disciplines

Animal and plant breeding

From the point of view of animal and plant breeders, there are several kinds of hybrid formed from crosses within a species, such as between different

. Single cross hybrids result from the cross between two true-breeding organisms which produces an F1 hybrid (first filial generation). The cross between two different

homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

lines produces an F1 hybrid that is

heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

; having two alleles, one contributed by each parent and typically one is dominant and the other

recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...

. Typically, the F1 generation is also phenotypically homogeneous, producing offspring that are all similar to each other. Double cross hybrids result from the cross between two different F1 hybrids (i.e., there are four unrelated grandparents). Three-way cross hybrids result from the cross between an F1 hybrid and an inbred line. Triple cross hybrids result from the crossing of two different three-way cross hybrids. Top cross (or "topcross") hybrids result from the crossing of a top quality or pure-bred male and a lower quality female, intended to improve the quality of the offspring, on average. Population hybrids result from the crossing of plants or animals in one

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using ...

with those of another population. These include interspecific hybrids or crosses between different breeds. In

, the term stable hybrid is used to describe an annual plant that, if grown and bred in a small

free of external

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

(e.g., an air-filtered greenhouse) produces offspring that are "true to type" with respect to phenotype; i.e., a true-breeding organism.

Biogeography

Hybridisation can occur in the

hybrid zone A hybrid zone exists where the ranges of two interbreeding species or diverged intraspecific lineages meet and cross-fertilize. Hybrid zones can form ''in situ'' due to the evolution of a new lineage but generally they result from secondary cont ...

s where the geographical ranges of species, subspecies, or distinct genetic lineages overlap. For example, the butterfly ''

Limenitis arthemis ''Limenitis arthemis,'' the red-spotted purple or white admiral, is a North American butterfly species in the cosmopolitan genus ''Limenitis''. It has been studied for its evolution of mimicry, and for the several stable hybrid wing patterns wi ...

'' has two major subspecies in North America, ''L. a. arthemis'' (the white admiral) and ''L. a. astyanax'' (the red-spotted purple). The white admiral has a bright, white band on its wings, while the red-spotted purple has cooler blue-green shades. Hybridisation occurs between a narrow area across New England, southern Ontario, and the Great Lakes, the "suture region". It is at these regions that the subspecies were formed. Other hybrid zones have formed between described species of plants and animals.

Genetics

From the point of view of genetics, several different kinds of hybrid can be distinguished. A genetic hybrid carries two different

allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

s of the same

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

, where for instance one allele may code for a lighter coat colour than the other. A structural hybrid results from the fusion of

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s that have differing structure in at least one chromosome, as a result of structural abnormalities. A numerical hybrid results from the fusion of gametes having different haploid numbers of chromosomes. A permanent hybrid results when only the heterozygous

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

occurs, as in '' Oenothera lamarckiana'', because all homozygous combinations are lethal. In the early history of genetics, Hugo de Vries supposed these were caused by mutation.

Taxonomy

From the point of view of

taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

, hybrids differ according to their parentage. Hybrids between different subspecies (such as between the Dog and Eurasian wolf) are called intra-specific hybrids. Interspecific hybrids are the offspring from interspecies mating; these sometimes result in hybrid speciation. Intergeneric hybrids result from matings between different genera, such as between

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated sh ...

and

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of ...

s. Interfamilial hybrids, such as between chickens and guineafowl or

pheasant Pheasants ( ) are birds of several genera within the family Phasianidae in the order Galliformes. Although they can be found all over the world in introduced (and captive) populations, the pheasant genera native range is restricted to Eurasia ...

s, are reliably described but extremely rare. Interordinal hybrids (between different orders) are few, but have been engineered between the

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) ...

Strongylocentrotus purpuratus ''Strongylocentrotus purpuratus'', the purple sea urchin, lives along the eastern edge of the Pacific Ocean extending from Ensenada, Mexico, to British Columbia, Canada. This sea urchin species is deep purple in color, and lives in lower int ...

'' (female) and the sand dollar ''

Dendraster excentricus ''Dendraster excentricus'', also known as the eccentric sand dollar, sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a species of sand dollar in the family Dendrasteridae. It is a flattened, burrowing sea urchin found in ...

'' (male).

Biology

Expression of parental traits

When two distinct types of organisms breed with each other, the resulting hybrids typically have intermediate traits (e.g., one plant parent has red flowers, the other has white, and the hybrid, pink flowers). Commonly, hybrids also combine traits seen only separately in one parent or the other (e.g., a

bird hybrid A bird hybrid is a bird that has two different species as parents. The resulting bird can present with any combination of characteristics from the parent species, from totally identical to completely different. Usually, the bird hybrid shows int ...

might combine the yellow head of one parent with the orange belly of the other).

Mechanisms of reproductive isolation

Interspecific hybrids are bred by mating individuals from two species, normally from within the same genus. The offspring display traits and characteristics of both parents, but are often sterile, preventing gene flow between the species. Sterility is often attributed to the different number of chromosomes between the two species. For example, donkeys have 62

chromosomes A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million ...

s have 64 chromosomes, and mules or

hinnies A hinny is a domestic equine hybrid, the offspring of a male horse (a stallion) and a female donkey (a jenny). It is the reciprocal cross to the more common mule, which is the product of a male donkey (a jack) and a female horse (a mare). The h ...

have 63 chromosomes. Mules, hinnies, and other normally sterile interspecific hybrids cannot produce viable gametes, because differences in chromosome structure prevent appropriate pairing and segregation during

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...

, meiosis is disrupted, and viable sperm and eggs are not formed. However, fertility in female mules has been reported with a donkey as the father. A variety of mechanisms limit the success of hybridisation, including the large genetic difference between most species. Barriers include morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization; others after it.Strickberger, M. 1978. ''Genética''. Omega, Barcelona, España, p.: 874–879. .Futuyma, D. 1998. ''Evolutionary biology'' (3ª edición). Sinauer, Sunderland. In plants, some barriers to hybridisation include blooming period differences, different pollinator vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the chromosomes.

Speciation

A few animal species are the result of hybridization. The Lonicera fly is a natural hybrid. The American red wolf appears to be a hybrid of the

gray wolf The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly u ...

and the coyote, although its taxonomic status has been a subject of controversy. The European edible frog is a semi-permanent hybrid between

pool frog The pool frog (''Pelophylax lessonae'') is a European frog in the family Ranidae. Its specific name was chosen by the Italian herpetologist Lorenzo Camerano in 1882, in order to honour his master Michele Lessona. Description The pool frog ...

s and

marsh frog The marsh frog (''Pelophylax ridibundus'') is a species of water frog native to Europe and parts of western Asia. Description The marsh frog is the largest type of frog in most of its range, with males growing to a size around 100 mm (3.9 ...

s; its population requires the continued presence of at least one of the parent species. Cave paintings indicate that the European bison is a natural hybrid of the

aurochs The aurochs (''Bos primigenius'') ( or ) is an extinct cattle species, considered to be the wild ancestor of modern domestic cattle. With a shoulder height of up to in bulls and in cows, it was one of the largest herbivores in the Holocene ...

and the steppe bison.

Plant Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

hybridization is more commonplace compared to animal hybridization. Many

crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydropo ...

species are hybrids, including notably the polyploid

s: some have four sets of chromosomes (tetraploid) or six (hexaploid), while other wheat species have (like most

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

organisms) two sets (

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respecti ...

), so hybridization events likely involved the doubling of chromosome sets, causing immediate genetic isolation. Hybridization may be important in speciation in some plant groups. However, homoploid hybrid speciation (not increasing the number of sets of chromosomes) may be rare: by 1997, only 8 natural examples had been fully described. Experimental studies suggest that hybridization offers a rapid route to speciation, a prediction confirmed by the fact that early generation hybrids and ancient hybrid species have matching genomes, meaning that once hybridization has occurred, the new

hybrid genome Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...

can remain stable. Many

s are known where the ranges of two species meet, and hybrids are continually produced in great numbers. These hybrid zones are useful as biological model systems for studying the mechanisms of speciation. Recently DNA analysis of a bear shot by a hunter in the North West Territories confirmed the existence of naturally-occurring and fertile grizzly–polar bear hybrids.

Hybrid vigour

Salvia jurisicii x nutans - Flickr - peganum

Hybridization between reproductively isolated species often results in hybrid offspring with lower fitness than either parental. However, hybrids are not, as might be expected, always intermediate between their parents (as if there were blending inheritance), but are sometimes stronger or perform better than either parental lineage or variety, a phenomenon called heterosis, hybrid vigour, or heterozygote advantage. This is most common with plant hybrids. A

transgressive phenotype In genetics, transgressive segregation is the formation of extreme phenotypes, or transgressive phenotypes, observed in segregated hybrid populations compared to phenotypes observed in the parental lines. The appearance of these transgressive (ex ...

is a phenotype that displays more extreme characteristics than either of the parent lines.

Plant breeders Plant breeding is the science of changing the traits of plants in order to produce desired characteristics. It has been used to improve the quality of nutrition in products for humans and animals. The goals of plant breeding are to produce cr ...

use several techniques to produce hybrids, including line breeding and the formation of complex hybrids. An economically important example is hybrid

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. ...

(corn), which provides a considerable seed yield advantage over open pollinated varieties. Hybrid seed dominates the commercial maize seed market in the United States, Canada and many other major maize-producing countries. In a hybrid, any trait that falls outside the range of parental variation (and is thus not simply intermediate between its parents) is considered heterotic. ''Positive heterosis'' produces more robust hybrids, they might be stronger or bigger; while the term ''negative heterosis'' refers to weaker or smaller hybrids. Heterosis is common in both animal and plant hybrids. For example, hybrids between a lion and a tigress (" ligers") are much larger than either of the two progenitors, while " tigons" (lioness × tiger) are smaller. Similarly, the hybrids between the common pheasant ('' Phasianus colchicus'') and domestic fowl ('' Gallus gallus'') are larger than either of their parents, as are those produced between the common pheasant and hen golden pheasant ('' Chrysolophus pictus''). Spurs are absent in hybrids of the former type, although present in both parents.

Human influence

Anthropogenic hybridization

Hybridization is greatly influenced by human impact on the environment, through effects such as

habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...

and species introductions. Such impacts make it difficult to conserve the genetics of populations undergoing introgressive hybridization. Humans have introduced species worldwide to environments for a long time, both intentionally for purposes such as

biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically als ...

, and unintentionally, as with accidental escapes of individuals. Introductions can drastically affect populations, including through hybridization.

Management

Aquilegia pubescens-formosa hybrid-swarm flowers close

There is a kind of continuum with three semi-distinct categories dealing with anthropogenic hybridization: hybridization without introgression, hybridization with widespread introgression (backcrossing with one of the parent species), and

hybrid swarm A hybrid swarm is a population of hybrids that has survived beyond the initial hybrid generation, with interbreeding between hybrid individuals and backcrossing with its parent types. Such population are highly variable, with the genetic and ...

s (highly variable populations with much interbreeding as well as backcrossing with the parent species). Depending on where a population falls along this continuum, the management plans for that population will change. Hybridization is currently an area of great discussion within

wildlife management Wildlife management is the management process influencing interactions among and between wildlife, its habitats and people to achieve predefined impacts. It attempts to balance the needs of wildlife with the needs of people using the best availab ...

and habitat management. Global climate change is creating other changes such as difference in population distributions which are indirect causes for an increase in anthropogenic hybridization. Conservationists disagree on when is the proper time to give up on a population that is becoming a hybrid swarm, or to try and save the still existing pure individuals. Once a population becomes a complete mixture, the goal becomes to conserve those hybrids to avoid their loss. Conservationists treat each case on its merits, depending on detecting hybrids within the population. It is nearly impossible to formulate a uniform hybridization policy, because hybridization can occur beneficially when it occurs "naturally", and when hybrid swarms are the only remaining evidence of prior species, they need to be conserved as well.

Genetic mixing and extinction

Regionally developed ecotypes can be threatened with

extinction Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...

when new alleles or genes are introduced that alter that ecotype. This is sometimes called genetic mixing. Hybridization and introgression, which can happen in natural and hybrid populations, of new genetic material can lead to the replacement of local

genotypes The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

if the hybrids are more fit and have breeding advantages over the indigenous ecotype or species. These hybridization events can result from the introduction of non-native genotypes by humans or through habitat modification, bringing previously isolated species into contact. Genetic mixing can be especially detrimental for rare species in isolated habitats, ultimately affecting the population to such a degree that none of the originally genetically distinct population remains.

Effect on biodiversity and food security

In agriculture and

animal husbandry Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, star ...

, the

Green Revolution The Green Revolution, also known as the Third Agricultural Revolution, was a period of technology transfer initiatives that saw greatly increased crop yields and agricultural production. These changes in agriculture began in developed countrie ...

's use of conventional hybridization increased yields by breeding " high-yielding varieties". The replacement of locally indigenous breeds, compounded with unintentional cross-pollination and crossbreeding (genetic mixing), has reduced the gene pools of various wild and indigenous breeds resulting in the loss of

genetic diversity Genetic diversity is the total number of Genetics, genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. ...

. Since the indigenous breeds are often well-adapted to local extremes in climate and have immunity to local pathogens, this can be a significant genetic erosion of the gene pool for future breeding. Therefore, commercial plant geneticists strive to breed "widely adapted" cultivars to counteract this tendency.

Different taxa

In animals

Mammals

Familiar examples of

equid hybrid Equid hybrids, also called hybrid equines, are created from the crossing of members from the horse family such as a horse, donkey and zebra.Equid Hybrids. (2014, June). Retrieved from http://www.best-top10-list.com/view/article/2811/equid-hybridsHYB ...

s are the mule, a cross between a female horse and a male donkey, and the hinny, a cross between a female donkey and a male horse. Pairs of complementary types like the mule and hinny are called reciprocal hybrids. Polar bears and

brown bear The brown bear (''Ursus arctos'') is a large bear species found across Eurasia and North America. In North America, the populations of brown bears are called grizzly bears, while the subspecies that inhabits the Kodiak Islands of Alaska is ...

s are another case of a hybridizing species pairs, and

introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Intro ...

among non-sister species of bears appears to have shaped the Ursidae family tree. Among many other mammal crosses are hybrid camels, crosses between a bactrian camel and a dromedary. There are many examples of felid hybrids, including the liger. The oldest known animal hybrid bred by humans is the kunga equid hybrid produced as a draft animal and status symbol 4500 years ago to ancient Syria. The first known instance of hybrid speciation in marine mammals was discovered in 2014. The clymene dolphin (''Stenella clymene'') is a hybrid of two Atlantic species, the spinner and striped dolphins. In 2019, scientists confirmed that a skull found 30 years earlier was a hybrid between the

beluga whale The beluga whale () (''Delphinapterus leucas'') is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus ''Delphinapterus''. It is also known as the whi ...

and narwhal; dubbed the narluga.

Birds

Cagebird breeders sometimes breed bird hybrids known as

mules A mule is the offspring of a female horse and a male donkey. Mule, Mules, MULE or The Mule can also refer to: Animals * Mule (sheep), in British sheep farming, a cross between a meat ram and a hardy mountain ewe * Mule deer (''Odocoileus hemio ...

between species of finch, such as

goldfinch Goldfinch or The Goldfinch may refer to: Birds * European goldfinch, ''Carduelis carduelis'' * Some species of the genus '' Spinus'': ** American goldfinch, ''Spinus tristis'' ** Lawrence's goldfinch, ''Spinus lawrencei'' ** Lesser goldfinc ...

× canary.

Amphibians

Among amphibians, Japanese giant salamanders and Chinese giant salamanders have created hybrids that threaten the survival of Japanese giant salamanders because of competition for similar resources in Japan.

Fish

Among fish, a group of about fifty natural hybrids between Australian blacktip shark and the larger common blacktip shark was found by Australia's eastern coast in 2012. Russian sturgeon and American paddlefish were hybridized in captivity when sperm from the paddlefish and eggs from the sturgeon were combined, unexpectedly resulting in viable offspring. This hybrid is called a

sturddlefish The sturddlefish is a hybrid of the American paddlefish (''Polyodon spathula'') and the Russian sturgeon (''Acipenser gueldenstaedtii''), accidentally created by researchers in 2019 and announced in 2020. Obtaining living hybrids through breeding ...

Cephalochordates

The two genera Asymmetron and

Branchiostoma ''Branchiostoma'' is one of the few living genus, genera of lancelets (order (biology), order Amphioxiformes). It is the type (zoology), type genus of family (biology), family Branchiostomatidae. These small vaguely eel- or snake-like animals a ...

are able to produce viable hybrid offspring, even if none have lived into adulthood so far, despite the parents' common ancestor living tens of millions of years ago.

Insects

Among insects, so-called killer bees were accidentally created during an attempt to breed a strain of bees that would both produce more honey and be better adapted to tropical conditions. It was done by crossing a European honey bee and an

African bee The East African lowland honey bee (''Apis mellifera scutellata'') is a subspecies of the western honey bee. It is native to central, southern and eastern Africa, though at the southern extreme it is replaced by the Cape honey bee (''Apis melli ...

. The ''

Colias eurytheme ''Colias eurytheme'', the orange sulphur, also known as the alfalfa butterfly and in its larval stage as the alfalfa caterpillar, is a butterfly of the family Pieridae, where it belongs to the lowland group of " clouded yellows and sulphurs" sub ...

'' and '' C. philodice'' butterflies have retained enough genetic compatibility to produce viable hybrid offspring. Hybrid speciation may have produced the diverse '' Heliconius''

butterflies Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group comprises t ...

, but that is disputed. The two closely related harvester ant species Pogonomyrmex barbatus and Pogonomyrmex rugosus have evolved to depend on hybridization. When a queen fertilize her eggs with sperm from males of her own species, the offspring is always new queens. And when she fertilize the eggs with sperm from males of the other species, the offspring is always sterile worker ants (and because ants are haplodiploid, unfertilized eggs become males). Without mating with males of the other species, the queens are unable to produce workers, and will fail to establish a colony of their own. File:Zeedonk 800.jpg, A " zonkey", a zebra/donkey hybrid File:Jaglion.jpg, A " jaglion", a jaguar/lion hybrid File:Goldfinch Canary hybrid.JPG, A domestic canary/goldfinch hybrid

In plants

Plant species hybridize more readily than animal species, and the resulting hybrids are fertile more often. Many plant species are the result of hybridization, combined with

polyploidy Polyploidy is a condition in which the cells of an organism have more than one pair of (homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...

, which duplicates the chromosomes. Chromosome duplication allows orderly meiosis and so viable seed can be produced. Plant hybrids are generally given names that include an "×" (not in italics), such as ''Platanus'' × ''acerifolia'' for the London plane, a natural hybrid of '' P. orientalis'' (oriental plane) and '' P. occidentalis'' (American sycamore). The parent's names may be kept in their entirety, as seen in ''

Prunus persica × Prunus americana ''Prunus persica'' × ''Prunus americana'' is the hybrid between the peach ''Prunus persica'' (often a nectarine) and the wild American plum ''Prunus americana''. Hybrids were obtained in the 1940s at the University of Minnesota, and have been ...

'', with the female parent's name given first, or if not known, the parent's names given alphabetically. Plant species that are genetically compatible may not hybridize in nature for various reasons, including geographical isolation, differences in flowering period, or differences in pollinators. Species that are brought together by humans in gardens may hybridize naturally, or hybridization can be facilitated by human efforts, such as altered flowering period or artificial pollination. Hybrids are sometimes created by humans to produce improved plants that have some of the characteristics of each of the parent species. Much work is now being done with hybrids between crops and their wild relatives to improve disease-resistance or

climate resilience Climate resilience is defined as the "capacity of social, economic and ecosystems to cope with a hazardous event or trend or disturbance".IPCC, 2022Summary for Policymakers .-O. Pörtner, D.C. Roberts, E.S. Poloczanska, K. Mintenbeck, M. Tignor, ...

for both agricultural and horticultural crops. Some crop plants are hybrids from different genera (intergeneric hybrids), such as Triticale, × ''Triticosecale'', a wheat–

rye Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is a member of the wheat tribe (Triticeae) and is closely related to both wheat (''Triticum'') and barley (genus ''Hordeum''). Rye grain is u ...

hybrid. Most modern and ancient wheat breeds are themselves hybrids; bread wheat, ''Triticum aestivum'', is a hexaploid hybrid of three wild grasses. Several commercial fruits including loganberry (''Rubus'' × ''loganobaccus'') and

grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit i ...

(''Citrus'' × ''paradisi'') are hybrids, as are garden herbs such as peppermint (''Mentha'' × ''piperita''), and trees such as the London plane (''Platanus'' × ''acerifolia''). Among many natural plant hybrids is '' Iris albicans'', a sterile hybrid that spreads by rhizome division, and '' Oenothera lamarckiana'', a flower that was the subject of important experiments by Hugo de Vries that produced an understanding of polyploidy. File:Trilliumhybrid2.jpg, A sterile hybrid between '' Trillium cernuum'' and '' T. grandiflorum'' File:Lily Lilium 'Citronella' Flower.jpg, An ornamental lily hybrid known as ''Lilium'' 'Citronella' Sterility in a non-polyploid hybrid is often a result of chromosome number; if parents are of differing chromosome pair number, the offspring will have an odd number of chromosomes, which leaves them unable to produce chromosomally-balanced gametes. While that is undesirable in a crop such as wheat, for which growing a crop that produces no seeds would be pointless, it is an attractive attribute in some fruits. Triploid

banana A banana is an elongated, edible fruit – botanically a berry (botany), berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa (genus), Musa''. In some countries, Cooking banana, bananas used for ...

s and

watermelon Watermelon (''Citrullus lanatus'') is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 var ...

s are intentionally bred because they produce no seeds and are also

parthenocarpic In botany and horticulture, parthenocarpy is the natural or artificially induced production of fruit without fertilisation of ovules, which makes the fruit seedless. Stenospermocarpy may also produce apparently seedless fruit, but the seeds are ac ...

In humans

There is evidence of hybridisation between modern humans and other species of the genus ''

Homo ''Homo'' () is the genus that emerged in the (otherwise extinct) genus '' Australopithecus'' that encompasses the extant species ''Homo sapiens'' (modern humans), plus several extinct species classified as either ancestral to or closely relat ...

''. In 2010, the Neanderthal genome project showed that 1–4% of DNA from all people living today, apart from most

Sub-Saharan African Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the African ...

s, is of Neanderthal heritage. Analyzing the genomes of 600 Europeans and East Asians found that combining them covered 20% of the Neanderthal genome that is in the modern human population. Ancient human populations lived and interbred with Neanderthals,

Denisovans The Denisovans or Denisova hominins ) are an extinct species or subspecies of archaic human that ranged across Asia during the Lower and Middle Paleolithic. Denisovans are known from few physical remains and consequently, most of what is kn ...

, and at least one other extinct ''Homo'' species. Thus, Neanderthal and Denisovan DNA has been incorporated into human DNA by introgression. In 1998, a complete prehistorical skeleton found in

Portugal Portugal, officially the Portuguese Republic, In recognized minority languages of Portugal: :* mwl, República Pertuesa is a country located on the Iberian Peninsula, in Southwestern Europe, and whose territory also includes the Macaronesian ...

, the

Lapedo child Lagar Velho 1, also known as the Lagar Velho boy or Lapedo child, is a complete prehistorical skeleton found in Portugal, believed to be a hybrid that had a Neanderthal parent and an anatomically modern human parent. In 1998, this discovery of an ...

, had features of both anatomically modern humans and

Neanderthal Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While ...

s. Some ancient human skulls with especially large nasal cavities and unusually shaped braincases represent human-Neanderthal hybrids. A 37,000- to 42,000-year-old human jawbone found in Romania's Oase cave contains traces of Neanderthal ancestry from only four to six generations earlier. All genes from Neanderthals in the current human population are descended from Neanderthal fathers and human mothers.

Mythology

Folk tales and myths sometimes contain mythological hybrids; the Minotaur was the offspring of a human,

Pasiphaë In ancient Greek religion and Greek mythology, Pasiphaë (; grc-gre, Πασιφάη, Pasipháē, lit=wide-shining derived from πάσι (archaic dative plural) "for all" and φάος/φῶς ''phaos/phos'' "light") was a queen of Crete, and wa ...

, and a white bull. More often, they are composites of the physical attributes of two or more kinds of animals, mythical beasts, and humans, with no suggestion that they are the result of interbreeding, as in the

(man/horse), chimera (goat/lion/snake),

hippocamp The hippocampus or hippocamp, also ''hippokampos'' (plural: hippocampi or hippocamps; grc, ἱππόκαμπος, from , "horse" and , "sea monster"

(fish/horse), and

(woman/lion). The

Old Testament The Old Testament (often abbreviated OT) is the first division of the Christian biblical canon, which is based primarily upon the 24 books of the Hebrew Bible or Tanakh, a collection of ancient religious Hebrew writings by the Israelites. The ...

mentions a first generation of half-human hybrid giants, the

, while the

apocryphal Apocrypha are works, usually written, of unknown authorship or of doubtful origin. The word ''apocryphal'' (ἀπόκρυφος) was first applied to writings which were kept secret because they were the vehicles of esoteric knowledge considered ...

Book of Enoch describes the Nephilim as the wicked sons of

s and attractive women.

Notes

References

External links

Artificial Hybridisation
– Artificial Hybridisation in orchids

Evolution Revolution: Two Species Become One, Study Says (nationalgeographic.com)

nbsp;– Creation of new species through hybridization was thought to be common only in plants, and rare in animals.
What is a human admixed embryo?
{{DEFAULTSORT:Hybrid (Biology) Biology terminology Botanical nomenclature Evolutionary biology Population genetics Breeding

Etymology

As seen by different disciplines

Animal and plant breeding

Biogeography

Genetics

Taxonomy

Biology

Expression of parental traits

Mechanisms of reproductive isolation

Speciation

Hybrid vigour

Human influence

Anthropogenic hybridization

Management

Genetic mixing and extinction

Effect on biodiversity and food security

Different taxa

In animals

Mammals

Birds

Amphibians

Fish

Cephalochordates

Insects

In plants

In humans

Mythology

See also

Notes

References

External links