Selective breeding

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Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant males and females will sexually reproduce and have offspring together. Selective breeding_sentence_0

Domesticated animals are known as breeds, normally bred by a professional breeder, while domesticated plants are known as varieties, cultigens, cultivars, or breeds. Selective breeding_sentence_1

Two purebred animals of different breeds produce a crossbreed, and crossbred plants are called hybrids. Selective breeding_sentence_2

Flowers, vegetables and fruit-trees may be bred by amateurs and commercial or non-commercial professionals: major crops are usually the provenance of the professionals. Selective breeding_sentence_3

In animal breeding, techniques such as inbreeding, linebreeding, and outcrossing are utilized. Selective breeding_sentence_4

In plant breeding, similar methods are used. Selective breeding_sentence_5

Charles Darwin discussed how selective breeding had been successful in producing change over time in his 1859 book, On the Origin of Species. Selective breeding_sentence_6

Its first chapter discusses selective breeding and domestication of such animals as pigeons, cats, cattle, and dogs. Selective breeding_sentence_7

Darwin used artificial selection as a springboard to introduce and support the theory of natural selection. Selective breeding_sentence_8

The deliberate exploitation of selective breeding to produce desired results has become very common in agriculture and experimental biology. Selective breeding_sentence_9

Selective breeding can be unintentional, e.g., resulting from the process of human cultivation; and it may also produce unintended – desirable or undesirable – results. Selective breeding_sentence_10

For example, in some grains, an increase in seed size may have resulted from certain ploughing practices rather than from the intentional selection of larger seeds. Selective breeding_sentence_11

Most likely, there has been an interdependence between natural and artificial factors that have resulted in plant domestication. Selective breeding_sentence_12

History Selective breeding_section_0

Selective breeding of both plants and animals has been practiced since early prehistory; key species such as wheat, rice, and dogs have been significantly different from their wild ancestors for millennia, and maize, which required especially large changes from teosinte, its wild form, was selectively bred in Mesoamerica. Selective breeding_sentence_13

Selective breeding was practiced by the Romans. Selective breeding_sentence_14

Treatises as much as 2,000 years old give advice on selecting animals for different purposes, and these ancient works cite still older authorities, such as Mago the Carthaginian. Selective breeding_sentence_15

The notion of selective breeding was later expressed by the Persian Muslim polymath Abu Rayhan Biruni in the 11th century. Selective breeding_sentence_16

He noted the idea in his book titled India, which included various examples. Selective breeding_sentence_17

Selective breeding was established as a scientific practice by Robert Bakewell during the British Agricultural Revolution in the 18th century. Selective breeding_sentence_18

Arguably, his most important breeding program was with sheep. Selective breeding_sentence_19

Using native stock, he was able to quickly select for large, yet fine-boned sheep, with long, lustrous wool. Selective breeding_sentence_20

The Lincoln Longwool was improved by Bakewell, and in turn the Lincoln was used to develop the subsequent breed, named the New (or Dishley) Leicester. Selective breeding_sentence_21

It was hornless and had a square, meaty body with straight top lines. Selective breeding_sentence_22

These sheep were exported widely, including to Australia and North America, and have contributed to numerous modern breeds, despite the fact that they fell quickly out of favor as market preferences in meat and textiles changed. Selective breeding_sentence_23

Bloodlines of these original New Leicesters survive today as the English Leicester (or Leicester Longwool), which is primarily kept for wool production. Selective breeding_sentence_24

Bakewell was also the first to breed cattle to be used primarily for beef. Selective breeding_sentence_25

Previously, cattle were first and foremost kept for pulling ploughs as oxen, but he crossed long-horned heifers and a Westmoreland bull to eventually create the Dishley Longhorn. Selective breeding_sentence_26

As more and more farmers followed his lead, farm animals increased dramatically in size and quality. Selective breeding_sentence_27

In 1700, the average weight of a bull sold for slaughter was 370 pounds (168 kg). Selective breeding_sentence_28

By 1786, that weight had more than doubled to 840 pounds (381 kg). Selective breeding_sentence_29

However, after his death, the Dishley Longhorn was replaced with short-horn versions. Selective breeding_sentence_30

He also bred the Improved Black Cart horse, which later became the Shire horse. Selective breeding_sentence_31

Charles Darwin coined the term 'selective breeding'; he was interested in the process as an illustration of his proposed wider process of natural selection. Selective breeding_sentence_32

Darwin noted that many domesticated animals and plants had special properties that were developed by intentional animal and plant breeding from individuals that showed desirable characteristics, and discouraging the breeding of individuals with less desirable characteristics. Selective breeding_sentence_33

Darwin used the term "artificial selection" twice in the 1859 first edition of his work On the Origin of Species, in Chapter IV: Natural Selection, and in Chapter VI: Difficulties on Theory: Selective breeding_sentence_34

Animal breeding Selective breeding_section_1

Main article: Animal breeding Selective breeding_sentence_35

Animals with homogeneous appearance, behavior, and other characteristics are known as particular breeds or pure breeds, and they are bred through culling animals with particular traits and selecting for further breeding those with other traits. Selective breeding_sentence_36

Purebred animals have a single, recognizable breed, and purebreds with recorded lineage are called pedigreed. Selective breeding_sentence_37

Crossbreeds are a mix of two purebreds, whereas mixed breeds are a mix of several breeds, often unknown. Selective breeding_sentence_38

Animal breeding begins with breeding stock, a group of animals used for the purpose of planned breeding. Selective breeding_sentence_39

When individuals are looking to breed animals, they look for certain valuable traits in purebred stock for a certain purpose, or may intend to use some type of crossbreeding to produce a new type of stock with different, and, it is presumed, superior abilities in a given area of endeavor. Selective breeding_sentence_40

For example, to breed chickens, a breeder typically intends to receive eggs, meat, and new, young birds for further reproduction. Selective breeding_sentence_41

Thus, the breeder has to study different breeds and types of chickens and analyze what can be expected from a certain set of characteristics before he or she starts breeding them. Selective breeding_sentence_42

Therefore, when purchasing initial breeding stock, the breeder seeks a group of birds that will most closely fit the purpose intended. Selective breeding_sentence_43

Purebred breeding aims to establish and maintain stable traits, that animals will pass to the next generation. Selective breeding_sentence_44

By "breeding the best to the best," employing a certain degree of inbreeding, considerable culling, and selection for "superior" qualities, one could develop a bloodline superior in certain respects to the original base stock. Selective breeding_sentence_45

Such animals can be recorded with a breed registry, the organization that maintains pedigrees and/or stud books. Selective breeding_sentence_46

However, single-trait breeding, breeding for only one trait over all others, can be problematic. Selective breeding_sentence_47

In one case mentioned by animal behaviorist Temple Grandin, roosters bred for fast growth or heavy muscles did not know how to perform typical rooster courtship dances, which alienated the roosters from hens and led the roosters to kill the hens after mating with them. Selective breeding_sentence_48

A Soviet attempt to breed lab rats with higher intelligence led to cases of neurosis severe enough to make the animals incapable of any problem solving unless drugs like phenazepam were used. Selective breeding_sentence_49

The observable phenomenon of hybrid vigor stands in contrast to the notion of breed purity. Selective breeding_sentence_50

However, on the other hand, indiscriminate breeding of crossbred or hybrid animals may also result in degradation of quality. Selective breeding_sentence_51

Studies in evolutionary physiology, behavioral genetics, and other areas of organismal biology have also made use of deliberate selective breeding, though longer generation times and greater difficulty in breeding can make these projects challenging in such vertebrates as house mice. Selective breeding_sentence_52

Plant breeding Selective breeding_section_2

Main article: Plant breeding Selective breeding_sentence_53

Plant breeding has been used for thousands of years, and began with the domestication of wild plants into uniform and predictable agricultural cultigens. Selective breeding_sentence_54

High-yielding varieties have been particularly important in agriculture. Selective breeding_sentence_55

Selective plant breeding is also used in research to produce transgenic animals that breed "true" (i.e., are homozygous) for artificially inserted or deleted genes. Selective breeding_sentence_56

Selective breeding in aquaculture Selective breeding_section_3

Selective breeding in aquaculture holds high potential for the genetic improvement of fish and shellfish. Selective breeding_sentence_57

Unlike terrestrial livestock, the potential benefits of selective breeding in aquaculture were not realized until recently. Selective breeding_sentence_58

This is because high mortality led to the selection of only a few broodstock, causing inbreeding depression, which then forced the use of wild broodstock. Selective breeding_sentence_59

This was evident in selective breeding programs for growth rate, which resulted in slow growth and high mortality. Selective breeding_sentence_60

Control of the reproduction cycle was one of the main reasons as it is a requisite for selective breeding programs. Selective breeding_sentence_61

Artificial reproduction was not achieved because of the difficulties in hatching or feeding some farmed species such as eel and yellowtail farming. Selective breeding_sentence_62

A suspected reason associated with the late realisation of success in selective breeding programs in aquaculture was the education of the concerned people – researchers, advisory personnel and fish farmers. Selective breeding_sentence_63

The education of fish biologists paid less attention to quantitative genetics and breeding plans. Selective breeding_sentence_64

Another was the failure of documentation of the genetic gains in successive generations. Selective breeding_sentence_65

This in turn led to failure in quantifying economic benefits that successful selective breeding programs produce. Selective breeding_sentence_66

Documentation of the genetic changes was considered important as they help in fine tuning further selection schemes. Selective breeding_sentence_67

Quality traits in aquaculture Selective breeding_section_4

Aquaculture species are reared for particular traits such as growth rate, survival rate, meat quality, resistance to diseases, age at sexual maturation, fecundity, shell traits like shell size, shell colour, etc. Selective breeding_sentence_68

Selective breeding_unordered_list_0

  • Growth rate – growth rate is normally measured as either body weight or body length. This trait is of great economic importance for all aquaculture species as faster growth rate speeds up the turnover of production. Improved growth rates show that farmed animals utilize their feed more efficiently through a positive correlated response.Selective breeding_item_0_0
  • Survival rate – survival rate may take into account the degrees of resistance to diseases. This may also see the stress response as fish under stress are highly vulnerable to diseases. The stress fish experience could be of biological, chemical or environmental influence.Selective breeding_item_0_1
  • Meat quality – the quality of fish is of great economic importance in the market. Fish quality usually takes into account size, meatiness, and percentage of fat, colour of flesh, taste, shape of the body, ideal oil and omega-3 content.Selective breeding_item_0_2
  • Age at sexual maturation – The age of maturity in aquaculture species is another very important attribute for farmers as during early maturation the species divert all their energy to gonad production affecting growth and meat production and are more susceptible to health problems (Gjerde 1986).Selective breeding_item_0_3
  • Fecundity – As the fecundity in fish and shellfish is usually high it is not considered as a major trait for improvement. However, selective breeding practices may consider the size of the egg and correlate it with survival and early growth rate.Selective breeding_item_0_4

Finfish response to selection Selective breeding_section_5

Salmonids Selective breeding_section_6

Gjedrem (1979) showed that selection of Atlantic salmon (Salmo salar) led to an increase in body weight by 30% per generation. Selective breeding_sentence_69

A comparative study on the performance of select Atlantic salmon with wild fish was conducted by AKVAFORSK Genetics Centre in Norway. Selective breeding_sentence_70

The traits, for which the selection was done included growth rate, feed consumption, protein retention, energy retention, and feed conversion efficiency. Selective breeding_sentence_71

Selected fish had a twice better growth rate, a 40% higher feed intake, and an increased protein and energy retention. Selective breeding_sentence_72

This led to an overall 20% better Fed Conversion Efficiency as compared to the wild stock. Selective breeding_sentence_73

Atlantic salmon have also been selected for resistance to bacterial and viral diseases. Selective breeding_sentence_74

Selection was done to check resistance to Infectious Pancreatic Necrosis Virus (IPNV). Selective breeding_sentence_75

The results showed 66.6% mortality for low-resistant species whereas the high-resistant species showed 29.3% mortality compared to wild species. Selective breeding_sentence_76

Rainbow trout (S. gairdneri) was reported to show large improvements in growth rate after 7–10 generations of selection. Selective breeding_sentence_77

Kincaid et al. Selective breeding_sentence_78

(1977) showed that growth gains by 30% could be achieved by selectively breeding rainbow trout for three generations. Selective breeding_sentence_79

A 7% increase in growth was recorded per generation for rainbow trout by Kause et al. Selective breeding_sentence_80

(2005). Selective breeding_sentence_81

In Japan, high resistance to IPNV in rainbow trout has been achieved by selectively breeding the stock. Selective breeding_sentence_82

Resistant strains were found to have an average mortality of 4.3% whereas 96.1% mortality was observed in a highly sensitive strain. Selective breeding_sentence_83

Coho salmon (Oncorhynchus kisutch) increase in weight was found to be more than 60% after four generations of selective breeding. Selective breeding_sentence_84

In Chile, Neira et al. Selective breeding_sentence_85

(2006) conducted experiments on early spawning dates in coho salmon. Selective breeding_sentence_86

After selectively breeding the fish for four generations, spawning dates were 13–15 days earlier. Selective breeding_sentence_87

Cyprinids Selective breeding_sentence_88

Selective breeding programs for the Common carp (Cyprinus carpio) include improvement in growth, shape and resistance to disease. Selective breeding_sentence_89

Experiments carried out in the USSR used crossings of broodstocks to increase genetic diversity and then selected the species for traits like growth rate, exterior traits and viability, and/or adaptation to environmental conditions like variations in temperature. Selective breeding_sentence_90

Kirpichnikov et al. Selective breeding_sentence_91

(1974) and Babouchkine (1987) selected carp for fast growth and tolerance to cold, the Ropsha carp. Selective breeding_sentence_92

The results showed a 30–40% to 77.4% improvement of cold tolerance but did not provide any data for growth rate. Selective breeding_sentence_93

An increase in growth rate was observed in the second generation in Vietnam. Selective breeding_sentence_94

Moav and Wohlfarth (1976) showed positive results when selecting for slower growth for three generations compared to selecting for faster growth. Selective breeding_sentence_95

Schaperclaus (1962) showed resistance to the dropsy disease wherein selected lines suffered low mortality (11.5%) compared to unselected (57%). Selective breeding_sentence_96

Channel Catfish Selective breeding_section_7

Growth was seen to increase by 12–20% in selectively bred Iictalurus punctatus. Selective breeding_sentence_97

More recently, the response of the Channel Catfish to selection for improved growth rate was found to be approximately 80%, i.e., an average of 13% per generation. Selective breeding_sentence_98

Shellfish response to selection Selective breeding_section_8

Oysters Selective breeding_section_9

Selection for live weight of Pacific oysters showed improvements ranging from 0.4% to 25.6% compared to the wild stock. Selective breeding_sentence_99

Sydney-rock oysters (Saccostrea commercialis) showed a 4% increase after one generation and a 15% increase after two generations. Selective breeding_sentence_100

Chilean oysters (Ostrea chilensis), selected for improvement in live weight and shell length showed a 10–13% gain in one generation. Selective breeding_sentence_101

Bonamia ostrea is a protistan parasite that causes catastrophic losses (nearly 98%) in European flat oyster Ostrea edulis L. This protistan parasite is endemic to three oyster-regions in Europe. Selective breeding_sentence_102

Selective breeding programs show that O. edulis susceptibility to the infection differs across oyster strains in Europe. Selective breeding_sentence_103

A study carried out by Culloty et al. Selective breeding_sentence_104

showed that ‘Rossmore' oysters in Cork harbour, Ireland had better resistance compared to other Irish strains. Selective breeding_sentence_105

A selective breeding program at Cork harbour uses broodstock from 3– to 4-year-old survivors and is further controlled until a viable percentage reaches market size. Selective breeding_sentence_106

Over the years ‘Rossmore' oysters have shown to develop lower prevalence of B. ostreae infection and percentage mortality. Selective breeding_sentence_107

Ragone Calvo et al. Selective breeding_sentence_108

(2003) selectively bred the eastern oyster, Crassostrea virginica, for resistance against co-occurring parasites Haplosporidium nelson (MSX) and Perkinsus marinus (Dermo). Selective breeding_sentence_109

They achieved dual resistance to the disease in four generations of selective breeding. Selective breeding_sentence_110

The oysters showed higher growth and survival rates and low susceptibility to the infections. Selective breeding_sentence_111

At the end of the experiment, artificially selected C. virginica showed a 34–48% higher survival rate. Selective breeding_sentence_112

Penaeid shrimps Selective breeding_section_10

Selection for growth in Penaeid shrimps yielded successful results. Selective breeding_sentence_113

A selective breeding program for Litopenaeus stylirostris saw an 18% increase in growth after the fourth generation and 21% growth after the fifth generation. Selective breeding_sentence_114

Marsupenaeus japonicas showed a 10.7% increase in growth after the first generation. Selective breeding_sentence_115

Argue et al. Selective breeding_sentence_116

(2002) conducted a selective breeding program on the Pacific White Shrimp, Litopenaeus vannamei at The Oceanic Institute, Waimanalo, USA from 1995 to 1998. Selective breeding_sentence_117

They reported significant responses to selection compared to the unselected control shrimps. Selective breeding_sentence_118

After one generation, a 21% increase was observed in growth and 18.4% increase in survival to TSV. Selective breeding_sentence_119

The Taura Syndrome Virus (TSV) causes mortalities of 70% or more in shrimps. Selective breeding_sentence_120

C.I. Selective breeding_sentence_121

Oceanos S.A. in Colombia selected the survivors of the disease from infected ponds and used them as parents for the next generation. Selective breeding_sentence_122

They achieved satisfying results in two or three generations wherein survival rates approached levels before the outbreak of the disease. Selective breeding_sentence_123

The resulting heavy losses (up to 90%) caused by Infectious hypodermal and haematopoietic necrosis virus (IHHNV) caused a number of shrimp farming industries started to selectively breed shrimps resistant to this disease. Selective breeding_sentence_124

Successful outcomes led to development of Super Shrimp, a selected line of L. stylirostris that is resistant to IHHNV infection. Selective breeding_sentence_125

Tang et al. Selective breeding_sentence_126

(2000) confirmed this by showing no mortalities in IHHNV- challenged Super Shrimp post larvae and juveniles. Selective breeding_sentence_127

Aquatic species versus terrestrial livestock Selective breeding_section_11

Selective breeding programs for aquatic species provide better outcomes compared to terrestrial livestock. Selective breeding_sentence_128

This higher response to selection of aquatic farmed species can be attributed to the following: Selective breeding_sentence_129

Selective breeding_unordered_list_1

  • High fecundity in both sexes fish and shellfish enabling higher selection intensity.Selective breeding_item_1_5
  • Large phenotypic and genetic variation in the selected traits.Selective breeding_item_1_6

Selective breeding in aquaculture provide remarkable economic benefits to the industry, the primary one being that it reduces production costs due to faster turnover rates. Selective breeding_sentence_130

This is because of faster growth rates, decreased maintenance rates, increased energy and protein retention, and better feed efficiency. Selective breeding_sentence_131

Applying such genetic improvement program to aquaculture species will increase productivity to meet the increasing demands of growing populations. Selective breeding_sentence_132

Advantages and disadvantages Selective breeding_section_12

Selective breeding is a direct way to determine if a specific trait can evolve in response to selection. Selective breeding_sentence_133

A single-generation method of breeding is not as accurate or direct. Selective breeding_sentence_134

The process is also more practical and easier to understand than sibling analysis. Selective breeding_sentence_135

Selective breeding is better for traits such as physiology and behavior that are hard to measure because it requires fewer individuals to test than single-generation testing. Selective breeding_sentence_136

However, there are disadvantages to this process. Selective breeding_sentence_137

Because a single experiment done in selective breeding cannot be used to assess an entire group of genetic variances, individual experiments must be done for every individual trait. Selective breeding_sentence_138

Also, because of the necessity of selective breeding experiments to require maintaining the organisms tested in a lab or greenhouse, it is impractical to use this breeding method on many organisms. Selective breeding_sentence_139

Controlled mating instances are difficult to carry out in this case and this is a necessary component of selective breeding. Selective breeding_sentence_140

See also Selective breeding_section_13

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: breeding.