Ancon sheep

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Ancon sheep
Conservation statusExtinct
Other namesOtter sheep
Country of originUnited States
Traits
Weight
  • Male:
    45 lb (20 kg)
Wool colorWhite
Face colorWhite
Notes
Dwarf

Ancon sheep (also called "Otter" sheep) were a grouping of domestic sheep with long bodies and very short legs, with the fore-legs being crooked. The term is generally applied to a line of sheep bred from a single affected lamb born in 1791 in Massachusetts, USA. The breed was artificially selected and maintained for its desirable inability to jump over fences. [1] It was allowed to go extinct in 1876 when it was no longer required. [2]

The name "Ancon" has also been applied to other strains of sheep arising from individuals with the same phenotype, such as a Norwegian stock bred from a single individual born in 1919, and a Texan, USA stock bred from a single individual born in 1962. These lineages were also allowed to go extinct after scientists no longer needed them for genetic research. [2] [3]

Excavations in Leicester, UK have also revealed metacarpals, metatarsals and phalanges characteristic of Ancon sheep that date to approximately AD 1500, thereby demonstrating that the phenotype has arisen independently at least four times. [2]

The unique features of ancon sheep are caused by a recessive dwarf mutation, which often results in crippling. The specific effect of the mutation is to cause chondrodystrophy. [2] [4]

Significance to the history of biology

Despite the Ancon's small numbers the sheep's contribution to the history of biology has been substantial. Several chapters in Charles Darwin's On the Origin of Species refer to the Ancon as an example of his argument that offspring inherit independent characteristics from their parents. The notion is perhaps best understood by the claim it denounces: the long-held belief among naturalists and breeders that inherited traits were a "blending" of the traits of each parent. [5] If that were true, the offspring of an Ancon and a common sheep would have a height between those of the parents. Instead, the resulting offspring were either Ancon or common, thus supporting Darwin's contention.

Darwin's review of the Ancon sheep helped lead to the establishment of an early consensus view of the sheep's role in understanding biology. Darwin referred to the Ancon as a "sport", or a new species or breed born suddenly from a prior species (as a form of phylogenetic variation, not to be confused with the "sporting plant" referred to in the study of botany) as opposed to a new species developing gradually over a long period of time through the natural selection of multiple traits.

Darwin believed that this was possible because the Ancon sheep were born and bred in captivity. In his 1868 work The Variation of Animals and Plants Under Domestication , Darwin argued that sudden mutations such as the Ancon are rare to non-existent outside of captivity. In his view, species change through the mutation and natural selection of minor traits which, when added up over time, gradually establish new species. [6] Later scholars supporting Darwin's view also pointed out that the Ancon sheep had essentially a single trait - their short legs - which also made rapid mutation unusually likely, since other species and breeds are set apart from their progenitors by many traits. [7]

Related Research Articles

<span class="mw-page-title-main">Heredity</span> Passing of traits to offspring from the species parents or ancestor

Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

<span class="mw-page-title-main">Mendelian inheritance</span> Type of biological inheritance

Mendelian inheritance is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized by William Bateson. These principles were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.

<span class="mw-page-title-main">Hybrid (biology)</span> Offspring of cross-species reproduction

In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different varieties, subspecies, species or genera through sexual reproduction. Generally, it means that each cell has genetic material from two different organisms, whereas an individual where some cells are derived from a different organism is called a chimera. 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, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are.

<span class="mw-page-title-main">Breed</span> Specific group of domestic animals

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 slightly deviating definitions. Breeds are formed through genetic isolation and either natural adaptation to the environment or selective breeding, or a combination of the two. Despite the centrality of the idea of "breeds" to animal husbandry and agriculture, no single, scientifically accepted definition of the term exists. A breed is therefore not an objective or biologically verifiable classification but is instead a term of art amongst groups of breeders who share a consensus around what qualities make some members of a given species members of a nameable subset.

<span class="mw-page-title-main">Dog breeding</span> Mating selected dogs for specific qualities

Dog breeding is the practice of mating selected dogs with the intention of maintaining or producing specific qualities and characteristics. When dogs reproduce without such human intervention, their offspring's characteristics are determined by natural selection, while "dog breeding" refers specifically to the artificial selection of dogs, in which dogs are intentionally bred by their owners. Breeding relies on the science of genetics, hence a breeder who is knowledgeable on canine genetics, health, and the intended purpose of the dogs attempts to breed suitable dogs.

<span class="mw-page-title-main">Zebroid</span> Offspring of a zebra and any other equine

A zebroid is the offspring of any cross between a zebra and any other equine to create a hybrid. In most cases, the sire is a zebra stallion. The offspring of a donkey sire and zebra dam, called a donkra, and the offspring of a horse sire and a zebra dam, called a hebra, do exist, but are rare and are usually sterile. Zebroids have been bred since the 19th century. Charles Darwin noted several zebra hybrids in his works.

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 maintain health and viability of organisms, irresponsible crossbreeding can also produce organisms of inferior quality or dilute a purebred gene pool to the point of extinction of a given breed of organism.

<span class="mw-page-title-main">Domestication of vertebrates</span>

The domestication of vertebrates is the mutual relationship between vertebrate animals including birds and mammals, and the humans who have influence on their care and reproduction.

Inbreeding depression is the reduced biological fitness that has the potential to result from inbreeding. The loss of genetic diversity that is seen due to inbreeding, results from small population size. Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. Inbreeding depression is often the result of a population bottleneck. In general, the higher the genetic variation or gene pool within a breeding population, the less likely it is to suffer from inbreeding depression, though inbreeding and outbreeding depression can simultaneously occur.

Chondrodystrophy refers to a skeletal disorder caused by one of myriad genetic mutations that can affect the development of cartilage. As a very general term, it is only used in the medical literature when a more precise description of the condition is unavailable.

<span class="mw-page-title-main">Test cross</span> Concept in classical genetics

Under the law of dominance in genetics, an individual expressing a dominant phenotype could contain either two copies of the dominant allele or one copy of each dominant and recessive allele. By performing a test cross, one can determine whether the individual is heterozygous or homozygous dominant.

Telegony is a theory of heredity holding that offspring can inherit the characteristics of a previous mate of the female parent; thus the child of a woman might partake of traits of a previous sexual partner. Experiments in the late 19th century on several species failed to provide evidence that offspring would inherit any character from their mother's previous mates. It was superseded by the rediscovery of Mendelian inheritance and the Boveri–Sutton chromosome theory. Encyclopædia Britannica says telegony “must now be classed as superstitions."

Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity.

<span class="mw-page-title-main">Labrador Retriever coat colour genetics</span> Genetics behind Labrador Retriever coat colour

The genetic basis of coat colour in the Labrador Retriever has been found to depend on several distinct genes. The interplay among these genes is used as an example of epistasis.

Foundation stock or foundation bloodstock refers to animals that are the progenitors, or foundation, of a breed or of a given bloodline within such. Many modern breeds can be traced to specific, named foundation animals, but a group of animals may be referred to collectively as foundation bloodstock when one distinct population provides part of the underlying genetic base for a new distinct population.

<span class="mw-page-title-main">Popular sire effect</span>

The popular sire effect occurs when an animal with desirable attributes is bred repeatedly. In dog breeding, a male dog that wins respected competitions becomes highly sought after, as breeders believe the sire possesses the genes necessary to produce champions. However, the popular sire effect is not just down to wanting to produce a champion. For example, in Staffordshire Bull Terriers there are several popular sires who are used by breeders to produce specific colours that are not favoured in the show ring. The popular sire is often bred extensively with many females. This can cause undetected, undesirable genetic traits in the stud to spread rapidly within the gene pool. It can also reduce genetic diversity by the exclusion of other males.

This article considers the history of zoology since the theory of evolution by natural selection proposed by Charles Darwin in 1859.

Classical genetics is the branch of genetics based solely on visible results of reproductive acts. It is the oldest discipline in the field of genetics, going back to the experiments on Mendelian inheritance by Gregor Mendel who made it possible to identify the basic mechanisms of heredity. Subsequently, these mechanisms have been studied and explained at the molecular level.

This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. Overlapping and related terms can be found in Glossary of cellular and molecular biology, Glossary of ecology, and Glossary of biology.

References

  1. McFadden, Johnjoe; Al-Khalili, Jim (2014). Life on the Edge : The Coming of Age of Quantum Biology (1st ed.). New York. p. 210. ISBN   978-0-307-98681-8. OCLC   914329162.{{cite book}}: CS1 maint: location missing publisher (link)
  2. 1 2 3 4 Gidney, Louisa (May–June 2007). "Earliest Archaeological Evidence of the Ancon Mutation in Sheep from Leicester, UK". International Journal of Osteoarchaeology. 17 (3): 318–321. doi:10.1002/oa.872. ISSN   1099-1212.
  3. Shelton, Maurice (1968). "A recurrence of the Ancon dwarf in Merino sheep". Journal of Heredity. 59 (5): 267–268. doi:10.1093/oxfordjournals.jhered.a107714. PMID   5753237.
  4. Chang, T. K. (1949). "Crippling in chondrodystrophic (Ancon) sheep". Growth. 13 (3): 299–307. PMID   18142372.
  5. Schwartz, Karlene; Vogel, Jane (Dec 1994). "Unraveling the Yarn of the Ancon Sheep" . BioScience. 44 (11). Oxford University Press: 764–768. doi:10.2307/1312585. ISSN   0006-3568. JSTOR   1312585 . Retrieved 2014-07-03. Ancon sheep are important to the history of biology because Charles Darwin used them to support his argument that animals inherit parental traits without blending: "When turnspit dogs and Ancon sheep, both of which have dwarfed limbs, are crossed with common breeds, the offspring are not intermediate in structure, but take after either parent." Before Darwin's day, many plant and animal breeders assumed that parental traits would mingle in the offspring.
  6. Schwartz, Jeffrey (January 13–16, 2005). "A Cultural History of Heredity III: 19th and Early 20th Centuries" (PDF). Darwinism versus Evo–Devo: a late–nineteenth century debate. A Cultural History of Heredity III: 19th and Early 20th Centuries. Max Planck Institute for the History of Science. pp. 67–84. Retrieved 7 March 2013.
  7. Eigenmann, C.H. (1895). "The Study of Variation". Proceedings of the Indiana Academy of Science. 5: 265–278. Retrieved 2014-03-07.