“polymorphism”的概念、定义、翻译、参考文献-科学参考

polymorphism

Chemistry

The existence of chemical substances in two (dimorphism) or more physical forms. See allotropy.

Computer

1. A feature of inheritance that allows a subclass object to be treated as if it were one of its superclasses. Where the subclass and the superclass have different implementations of a method, that of the subclass is used. Polymorphism is a major contributor to the power of object-orientated languages.
2. A feature of several modern high-level programming languages that allows arguments to procedures and functions to vary systematically over a whole class of data types, rather than being restricted to a single type. A simple example would be a function to find the length of a list. The code for such a function should be the same for lists of integers, lists of Booleans, or lists of anything. In a language like Algol, however, the argument to such a function must have a single type; hence to handle both lists of integers and lists of Booleans, two functions would have to be defined. This can be avoided in languages that support polymorphic types like ‘list of alpha’, where alpha is a type variable standing for an arbitrary type. A polymorphic function is one that takes one or more arguments of polymorphic types.
Polymorphism was first used in the ML language. Its implementations in modern languages are usually called generics (Ada, Java, C#, VB.NET) or templates (C++).

Biology

The existence of two or more distinctly different forms (morphs) within a plant or animal species, particularly due to genetic differences. Two forms of genetic polymorphism exist: transient polymorphism, in which a particular form is in the process of spreading through a population, causing the relative proportion of phenotypes to alter; and balanced polymorphism, in which two or more forms coexist in a stable ratio within a population, each form possessing both advantageous and disadvantageous characteristics. An example of balanced polymorphism is the occurrence of sickle-cell disease, a genetic disease that principally affects Black populations of central Africa and is characterized by an abnormal form of the blood pigment haemoglobin (haemoglobin S) and sickle-shaped red blood cells. Three different types of individual occur in such populations: those who have two alleles (AA) for normal haemoglobin and therefore do not suffer from the disease; those with one normal and one abnormal allele (AS), who are described as having the sickle-cell trait and generally suffer no symptoms; and those with two abnormal alleles (SS), who suffer a chronic and eventually fatal form of anaemia. Normally such a harmful allele would have been eliminated from the population by the process of natural selection, but it is maintained in this case because people with the sickle-cell trait are resistant to a severe form of malaria endemic in central Africa. They exhibit heterozygote advantage (see balancing selection). Environmental polymorphism is not due to genetic differences, an example being the caste system of social insects, in which the different morphs—i.e. workers, drones, and queens—are determined by the larvae receiving different types of food. Many authorities prefer the term polyphenism for this phenomenon. Compare mutation.
See also restriction fragment length polymorphism; single nucleotide polymorphism.

Geology and Earth Sciences

Ability of elements or compounds to exist in more than one crystal form, with each having the same chemical composition but different physical properties due to differences in the arrangement of atoms. Examples are graphite and diamond (both C); alpha and beta quartz (both SiO₂); and calcite (hexagonal) and aragonite (orthorhombic), both forms of CaCO₃. The terms ‘dimorphism’ and ‘trimorphism’ describe (respectively) two and three different forms.

单词	polymorphism
释义	polymorphism Chemistry The existence of chemical substances in two (dimorphism) or more physical forms. See allotropy. Computer 1. A feature of inheritance that allows a subclass object to be treated as if it were one of its superclasses. Where the subclass and the superclass have different implementations of a method, that of the subclass is used. Polymorphism is a major contributor to the power of object-orientated languages. 2. A feature of several modern high-level programming languages that allows arguments to procedures and functions to vary systematically over a whole class of data types, rather than being restricted to a single type. A simple example would be a function to find the length of a list. The code for such a function should be the same for lists of integers, lists of Booleans, or lists of anything. In a language like Algol, however, the argument to such a function must have a single type; hence to handle both lists of integers and lists of Booleans, two functions would have to be defined. This can be avoided in languages that support polymorphic types like ‘list of alpha’, where alpha is a type variable standing for an arbitrary type. A polymorphic function is one that takes one or more arguments of polymorphic types. Polymorphism was first used in the ML language. Its implementations in modern languages are usually called generics (Ada, Java, C#, VB.NET) or templates (C++). Biology The existence of two or more distinctly different forms (morphs) within a plant or animal species, particularly due to genetic differences. Two forms of genetic polymorphism exist: transient polymorphism, in which a particular form is in the process of spreading through a population, causing the relative proportion of phenotypes to alter; and balanced polymorphism, in which two or more forms coexist in a stable ratio within a population, each form possessing both advantageous and disadvantageous characteristics. An example of balanced polymorphism is the occurrence of sickle-cell disease, a genetic disease that principally affects Black populations of central Africa and is characterized by an abnormal form of the blood pigment haemoglobin (haemoglobin S) and sickle-shaped red blood cells. Three different types of individual occur in such populations: those who have two alleles (AA) for normal haemoglobin and therefore do not suffer from the disease; those with one normal and one abnormal allele (AS), who are described as having the sickle-cell trait and generally suffer no symptoms; and those with two abnormal alleles (SS), who suffer a chronic and eventually fatal form of anaemia. Normally such a harmful allele would have been eliminated from the population by the process of natural selection, but it is maintained in this case because people with the sickle-cell trait are resistant to a severe form of malaria endemic in central Africa. They exhibit heterozygote advantage (see balancing selection). Environmental polymorphism is not due to genetic differences, an example being the caste system of social insects, in which the different morphs—i.e. workers, drones, and queens—are determined by the larvae receiving different types of food. Many authorities prefer the term polyphenism for this phenomenon. Compare mutation. See also restriction fragment length polymorphism; single nucleotide polymorphism. Geology and Earth Sciences Ability of elements or compounds to exist in more than one crystal form, with each having the same chemical composition but different physical properties due to differences in the arrangement of atoms. Examples are graphite and diamond (both C); alpha and beta quartz (both SiO₂); and calcite (hexagonal) and aragonite (orthorhombic), both forms of CaCO₃. The terms ‘dimorphism’ and ‘trimorphism’ describe (respectively) two and three different forms.
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