What is "polymorphism"

Polymorphism \Pol`y*mor"phism\, n.

1. (Crystallog.) Same as Pleomorphism.

2. (Biol.)

   1. The capability of assuming different forms; the capability of widely varying in form.

   2. Existence in many forms; the coexistence, in the same locality, of two or more distinct forms independent of sex, not connected by intermediate gradations, but produced from common parents.

1839, from polymorph + -ism.

n. 1 The ability to assume different forms or shapes. 2 (context biology English) The coexistence, in the same locality, of two or more distinct forms independent of sex, not connected by intermediate gradations, but produced from common parents. 3 (context computer science English) The feature of object-oriented programming pertaining to the dynamic treatment of data elements based on their type, allowing for an instance of a method to have several definitions. (attention: en) 4 (context mathematics type theory English) The property of certain typed formal systems of allowing for the use of type variables and binders/quantifiers over those type variables; likewise, the property of certain expressions (within such typed formal systems) of making use of at least one such typed variable. 5 (context crystallography English) The ability of a solid material to exist in more than one form or crystal structure; pleomorphism. 6 (context genetics English) The regular existence of two or more different genotypes within a given species or population; also, variability of amino acid sequences within a gene's protein.

1. n. (chemistry) the existence of different kinds of crystal of the same chemical compound [syn: pleomorphism]

2. (biology) the existence of two or more forms of individuals within the same animal species (independent of sex differences)

Polymorphism, polymorphic or polymorph, from the Greek roots "poly" (many) and "morphe" (form, shape, structure), may refer to:

In programming languages and type theory, polymorphism (from Greek πολύς, polys, "many, much" and μορφή, morphē, "form, shape") is the provision of a single interface to entities of different types. A polymorphic type is one whose operations can also be applied to values of some other type, or types. There are several fundamentally different kinds of polymorphism:

• Ad hoc polymorphism: when a function denotes different and potentially heterogeneous implementations depending on a limited range of individually specified types and combinations. Ad hoc polymorphism is supported in many languages using function overloading.
• Parametric polymorphism: when code is written without mention of any specific type and thus can be used transparently with any number of new types. In the object-oriented programming community, this is often known as generics or generic programming. In the functional programming community, this is often shortened to polymorphism.
• Subtyping (also called subtype polymorphism or inclusion polymorphism): when a name denotes instances of many different classes related by some common superclass. In the object-oriented programming community, this is often simply referred to as polymorphism.

The interaction between parametric polymorphism and subtyping leads to the concepts of variance and bounded quantification.

Polymorphism in biology and zoology is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. In order to be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population (one with random mating).

Three mechanisms may cause polymorphism:

• Genetic polymorphism - where the phenotype of each individual is genetically determined.
• A conditional development strategy, where the phenotype of each individual is set by environmental cues.
• A mixed development strategy, where the phenotype is randomly assigned during development.

Polymorphism as used in zoology and biology involves morphs of the phenotype, and the term polyphenism can be used to clarify that the different forms arise from the same genotype. The term genetic polymorphism is also used somewhat differently by geneticists and molecular biologists to describe certain mutations in the genotype, such as SNPs (with detection methods RFLPs and AFLPs), that may not always correspond to a phenotype but always corresponds to a branch in the genetic tree. See below.

Polymorphism is common in nature; it is related to biodiversity, genetic variation and adaptation; it usually functions to retain variety of form in a population living in a varied environment. The most common example is sexual dimorphism, which occurs in many organisms. Other examples are mimetic forms of butterflies (see mimicry), and human hemoglobin and blood types.

According to the theory of evolution, polymorphism results from evolutionary processes, as does any aspect of a species. It is heritable and is modified by natural selection. In polyphenism, an individual's genetic make-up allows for different morphs, and the switch mechanism that determines which morph is shown is environmental. In genetic polymorphism, the genetic make-up determines the morph. Ants exhibit both types in a single population.

Polymorphism also refers to the occurrence of structurally and functionally more than two different types of individuals, called zooids within the same organism. It is a characteristic feature of Cnidarians. For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae.

In materials science, polymorphism is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements. The complete morphology of a material is described by polymorphism and other variables such as crystal habit, amorphous fraction or crystallographic defects. Polymorphism is relevant to the fields of pharmaceuticals, agrochemicals, pigments, dyestuffs, foods, and explosives.

When polymorphism exists as a result of difference in crystal packing, it is called packing polymorphism. Polymorphism can also result from the existence of different conformers of the same molecule in conformational polymorphism. In pseudopolymorphism the different crystal types are the result of hydration or solvation. This is more correctly referred to as solvomorphism as different solvates have different chemical formulae. An example of an organic polymorph is glycine, which is able to form monoclinic and hexagonal crystals. Silica is known to form many polymorphs, the most important of which are; α-quartz, β-quartz, tridymite, cristobalite, coesite, and stishovite. A classical example is the pair of minerals, calcite and aragonite, both forms of calcium carbonate.

An analogous phenomenon for amorphous materials is polyamorphism, when a substance can take on several different amorphous modifications.