The word "phenotype" is of Greek origin and is translated (literally) "discover", "reveal". What is the practical meaning of this concept?
What is a phenotype? Definition
A phenotype should be understood as a set of characteristics that are inherent in an individual at a particular stage of development. This set is formed on the basis of the genotype. For diploid organisms, the manifestation of dominant genes is characteristic. Defining more precisely what a phenotype is, one should talk about the totality of internal and external signs of an organism that were acquired in the process of individual development (ontogenesis).
General information
Despite a fairly precise definition of what a phenotype is, its concept has a number of uncertainties. Most of the structures and molecules that are encoded by the genetic material are not found in the external appearance of the organism. However, they are part of the phenotype. An example would be the blood phenotype of humans. In this regard, according to a number of authors, the definition should also include those characteristics that can be obtained using diagnostic, medical or technical procedures. Morea radical further extension may contain acquired behavior, and if necessary, the influence of the organism on the environment and other organisms. So, for example, the incisors and dam of beavers can be mistaken for their phenotype.
Key Features
Determining what a phenotype is, we can talk about some "removal" of genetic information towards environmental factors. As a first approximation, two characteristics should be considered:
- Dimension of the phenotype. This feature indicates the number of "outward" directions, which characterizes the number of environmental factors.
- The second sign indicates the level of sensitivity of the phenotype to environmental conditions. This degree is called range.
In combination, these characteristics indicate the richness and variety of the phenotype. The more multidimensional the set of individual characteristics, the more sensitive the signs and the farther they are from the genotype, the richer it is. So, for example, if we compare the phenotype of a bacterium, roundworm, frog, human, then the "we alth" in this chain increases. This means that the human phenotype is richer.
Historical background
In 1909, Wilhelm Johansen (a Danish scientist) for the first time - in combination with the concept of the genotype - proposed the definition of the phenotype. This made it possible to distinguish heredity from the result of its implementation. The idea of differences can also be traced back to the work of Mendel and Weismann. At the same time, the latter distinguished somatic andreproductive cells in multicellular organisms. The chromosome set received from the parents is contained in the cell nuclei. Chromosomes carry a complex of genes characteristic of a particular species in general and a particular organism in particular. Genes contain information about proteins that can be synthesized, as well as about the mechanisms that, in fact, determine and regulate synthesis. What then happens? During ontogenesis, genes are sequentially switched on and the proteins that they encode are synthesized. As a result, the formation and development of all the properties and characteristics of the organism that make up its phenotype occurs. In other words, a certain "product" is obtained from the implementation of the genetic program contained in the genotype.
Influence of external conditions on the development of individual traits
It should be noted that the genotype is not an unambiguous factor that determines the phenotype. To one degree or another, the formation of a set of individual characteristics will also depend on the environment of stay, that is, on external factors. Under different conditions, phenotypes have a sharp difference. So, for example, the type of butterflies "arashnia" gives two offspring per year. Those individuals that emerged from overwintered pupae (spring) differ sharply from those that appeared in the summer. The phenotype of the plant may also differ. For example, in the open space the pines are spreading, and in the forest they are slender and tall. In the water buttercup, the shape of the leaf depends on where it is - in the air or in the water.
Relationship between phenotypes and genotypes
The ability to change, which is provided by the genetic program, is called the norm of reaction. As a rule, the more diverse the conditions in which the species lives, the wider this norm. In the event that the environment differs sharply from that to which the species is adapted, a violation occurs in the development of organisms, and they die. The traits of the phenotype do not always reflect recessive alleles. But at the same time they are preserved and can pass to offspring. This information allows us to better understand the evolutionary process. Only phenotypes participate in natural selection, while genotypes are transmitted to offspring and remain further in the population. The interaction is not limited to the relationship between recessive and dominant alleles - many genes interact with each other.
