Polymorphism occurs when in one form there are several different physical forms or types of individuals. Take, for example, the birch moth - a nocturnal insect that teachers often use in the lessons of evolutionary biology and natural selection. These moths are an excellent example of polymorphism in nature. Although two butterflies belong to the same species, they can look completely different from each other.
The meaning of the term
In biology, polymorphism (from the Greek: “poly”, which means “a lot” and “morph”, which means “form”) can be applied to biochemical, morphological and behavioral characteristics, but it must be intermittent. This is also a common variation in DNA sequence for a population group.
Monomorphism is known (only one form is present) and dimorphism (two), as for polymorphism in biology and genetics, this term is very specific. It does not apply to character traits with continuous change, for example, growth (although it may be inherited). Earlobes are either fused or not (polymorphism with inheritance), and growth does not have precisely defined changing values.
Polymorphism is an expression of the genetic diversity of a species. It gives each species flexibility and adaptability in the environment. In addition, it is a basis for the population level, based on the action of natural selection, leading to a change in the frequency of alleles, and then microevolution. Polymorphism is not only the variability that can be observed in the environment, but also the division of labor into effective social organization and the use of natural resources. In many polymorphic species, a social organization brings together discrete members similar to the harmony observed among different organs of one biological organism, thereby ensuring the well-being of the entire population and the species as a whole.
Types of Polymorphism
The main types of the phenomenon: sexual dysmorphism and allelic polymorphism.
Sexual dimorphism occurs when physical differences are found between male and female members of the same species. For example, in the photo below - male and female of one species of ducks. Allelic polymorphism occurs when multiple alleles are expressed in a population. These are different versions of features or physical characteristics.
Adaptation (transitional) polymorphism occurs in the presence of two alleles in the gene pool. Moreover, one gene gradually replaces another. This is due to the strong environmental impact, which stimulates the elimination of one allele from the gene pool.
Balanced polymorphism occurs when there are two alleles in the gene pool. The frequency of their repetition does not change. This is due to selective pressure promoting the coexistence of two alleles (heterozygous advantage) through stabilizing selection.
Examples of polymorphism
There are many examples of polymorphism in biology. These are various types of human blood (A, B, AB or O), and sexual dimorphism (male or female).
The intermittent division of labor in a colony of ants or bees, such as the queen, reproductive males, workers, soldiers, is also a type of polymorphism. This social organization harmoniously unites individual members, as if they were different organs of one biological organism.
Adaptation: light and dark moth color options. This is a direction of selection determined by the environment.
Balanced: sickle cell anemia in African countries (heterozygotes do not increase anemia, but are resistant to malaria).
Genetic polymorphism
Variations in the body's DNA sequence without any phenotypic effect are called neutral polymorphisms. Examples thereof may include single nucleotide polymorphisms (SNPs) and restriction fragment length polymorphisms (RFLPs). In SNP, one of the nucleotides of the codon undergoes changes without turning into a codon of various amino acids. RFLP is a polymorphism, usually due to SNP, and is characterized by a change in the length of the DNA sequence.
Two or more equally acceptable alternatives are needed to classify polymorphism in biology. The least common allele should have a frequency of 1% or more. Otherwise, it is considered a mutation.