There are a huge number of different life forms on planet Earth, and there are not even two identical animals or plants on it. Different species are very different from each other, but even among very similar at first glance individuals of the same species there are no two completely identical to each other.
And what is most surprising, all of the above is true not only for creatures that reproduce sexually, but also for those who reproduce vegetatively, and even for clones.
So why do living organisms on Earth owe such an individuality? The fact is that from the moment of its formation - no matter in the form of a zygote or a daughter process - the body begins to change. And he changes all his life - until his death. This property of all living things has been called variability.
However, variability does not always proceed according to the same program, and therefore, as it was studied, scientists identified types of variability.
So, variability can be both individual (occurring with one being), and group (occurring with the whole group). The first is the most common.
Geographic variability is also distinguished as a separate species, the distinguishing feature of which is the fact that changes with the creature occur under the influence of external factors of a certain territory.
The types of variability are also divided according to the degree of transformation: if it is complete, radical, then this is qualitative variability, and if the transformation is only partial, incomplete, then this is quantitative variability.
If a living creature is affected by certain external factors that provoke the transformation of attributes, then this is directed variability, and if the transformation occurs spontaneously, then this is non-directed variability. In addition, there is ontogenetic variability, which is a change that occurs throughout the development and life of the organism.
Despite the fact that there are so many options for the possible transformation of characteristics characteristic of a creature, not all the qualities acquired by him are transferred to his descendants. Therefore, the following types of variability are also distinguished : hereditary and non-hereditary (modification).
However, this does not end there. It is hereditary and non-hereditary types of variation that are divided into subspecies. These subspecies differ in a whole complex of characters and properties. And they are called, for convenience, forms.
So, the following forms of variability are distinguished : modification and genotypic. Modification, also called phenotypic, is manifested by the fact that in different individuals of the same species, the phenotype changes under the influence of the environment. The changes received by organisms are individual; they are not inherited.
For example, if the dandelion root is cut in half and planted under different conditions (one half in the mountains, the other in the lowland), then by the time the plants reach puberty, it will be obvious that the plant phenotype is radically different. A dandelion grown in the mountains will be stunted; its leaves and flower will not be large. But the plant grown in the valley, by contrast, will be tall, and its leaves - large. And if the descendants of these plants are grown under the same conditions, then there will be no differences between them.
The main significance of this modification is the ability of a living organism to adapt to its current environment.
Genotypic variation is fundamentally different from modification, since as a result of it it is not the phenotype that changes, but the genotype, and a new, acquired trait is inherited. Genotypic variation is divided into two subspecies: combinational and mutational (mutation).
Combinational variability is the emergence of new properties in a descendant due to any new gene combinations in his parents. So, for example, when crossing sweet peas with white flowers, their offspring may have a purple color.
A mutation is a sudden, but at the same time, steady change in the genetic material of the body itself, transmitted to descendants. Mutations are individual and directed.