Questions in ecology, evolutionary theory, population biology and other sciences often involve the concept of variability (both definite and indefinite). This is the cornerstone for understanding the origin of species, their ability to adapt to changing environmental conditions. These principles underlie modern breeding and molecular biology. Let's try to figure out what these concepts mean.
Types of variability
These concepts are also called non-hereditary and hereditary variability. What is the difference between definite and indefinite variability? The first occurs in a group of individuals as a response to external factors. It is regulated by the value of the reaction norm. As an example, we can recall the hibernation of a bear, the density of a dog's coat, the length of a dandelion stem. If you change the environmental conditions, then these signs may not appear. So, if you artificially create an abundance of food and a warm temperature all year round, then the bear will not sleep through the winter. A dog that lives indoors in winter will have much less undercoat than a chain yard dog. With constant lawn mowing, dandelionwill grow with a shorter stem length, which will allow it to form a peduncle and avoid cutting. Of course, such traits are not genetically inherited.
Hereditary variability occurs as spontaneous mutations within a group of individuals and is inherited through generations. However, not all mutations are beneficial. Most of them become useless or harmful. Only some changes will be supported by natural selection. This property is the basis of evolution, as it allows the organism to adapt to changes in the environment, to acquire qualities that contribute to survival. Let's dwell on this type in more detail.
History of the study of uncertain variability
When mentioning the factors influencing the origin of species, one cannot fail to mention the author of the book of the same name and the theory of evolution, Charles Darwin. Of course, at the moment this theory has been finalized and is called synthetic. However, the description of the basic concepts and the principle remained unchanged.
According to Darwin, indeterminate variability – is "infinitely varied minor features that distinguish individuals of the same species and which cannot be explained by inheritance from one of their parents or from more distant ancestors." He also spoke about the direct and indirect influence of the conditions of existence on the formation of a living organism, about the correlation of signs. At the same time, the concept of a gene did not yet exist, and the reasons for the appearance of datafeatures were not clear to this scientist. It is now known that inheritance is genetic in nature, and mutations occur in DNA all the time.
How does this mechanism work?
DNA replication is constantly getting errors. Normally, they must be removed by the immune system or the system of cellular apoptosis (programmed death). In the event of failure of these systems, this cell can survive and create copies of itself. If the organism is single-celled or changes have affected the sex cells, this defect will be inherited and passed on to other generations. This creates diversity in the population and guarantees the survival of the species and evolution in general.
Types of mutations
- Gene. Affect the structure of DNA at the nucleotide level. They are expressed in the loss, replacement of any nucleotide (human diseases such as phenylketonuria, sickle cell anemia can be cited as an example).
- Generative. Affect the genes of germ cells. Inherited through generations.
- Somatic. Mutations of non-sex cells. They are not inherited in animals, but are inherited in plants when propagated by a vegetative method (in in-vitro cell culture).
- Genomic. Associated with a change in the number of chromosomes in the nucleus. They can manifest as an increase in one or more chromosomes (in humans, Down's disease is associated with an extra chromosome) and as a multiplication of their number (polyploid plants are indicative: most modern wheat varieties are octoploid, that is, they have eight sets of chromosomes).
- Chromosomal.
Meaning
- The species does not always live in the same conditions. In the event of a change in living conditions, sometimes abrupt, for example, due to a natural disaster, resettlement to another continent, etc., the entire population may be subject to extinction. But some organisms may have mutations that were useless up to this point, but are now necessary for survival. This means that only these individuals will survive and give offspring with these traits. An example would be the constant battle between bacteria and antibiotics. The developed antibacterial agents are quite effective for a certain time, until the offspring of microorganisms with genes for resistance to this type of medication multiply. This forces the pharmaceutical industry to create new products and unwittingly stimulate bacteria to further evolve.
- Value in selection. It was this type of variation that Charles Darwin considered the basis for artificial selection. Mutations that appear initially, regardless of environmental factors, can be valuable to humans. So, for example, large-fruited tomato fruits are not useful for the plant itself - the branches will not withstand their weight without props and garters. But selection on this basis allowed us to obtain more productive varieties.
Definition: what is indeterminate variability in biology
Summing up the above, we summarize what this concept means in science. Indefinite variability in biology is a concept synonymous withmutations. It is hereditary in nature (as opposed to a definite one), while minor changes in the genome in the first generation accumulate and intensify in subsequent ones. This type of variability is also associated with changes in environmental factors, but not in the form of adaptations, but indirectly. Thus, it helps to adapt not to a specific organism, but to the taxon as a whole.
Examples of uncertain variability
Earlier in the article, particular examples of mutations that help to adapt to the environment were discussed. Consider several broad types of such variability in nature:
- Protective coloration. Occurs in many animals. In the process of natural selection, individuals with a more inconspicuous coloration in the surrounding landscape are less susceptible to attack by predators and, therefore, can produce more offspring. This feature is fixed in generations. At the same time, when environmental conditions change (for example, when a population moves to another habitat), the color maintained by selection may change.
- Signal coloring. As a result of changes in the genome, some insects have acquired bright colors that warn predators of venom glands. Non-venomous insects can also be colored this way to protect them from being eaten. This phenomenon is called mimicry.
- Body shape. The indirect influence of the environment supports individuals whose body shape is most adapted to it. So, the torpedo-shaped form, which helps in swimming, is characteristic of aquatic organisms. It is similar in dolphins, seals, penguins, fish, swimming beetles. Naturally, this form in these animals developed independently. It's just that in the process of evolution, those individuals that were best adapted to swimming survived and gave birth.
- Protection mechanisms. For example, the needles of a hedgehog, a porcupine - a modified hairline. Individuals that, due to a spontaneous mutation, received denser bristles, which can cause inconvenience to a predator, gained an advantage in reproduction. In the next generations, apparently, the selection supported the sharpness of the coat - this feature intensified.
Summing up
This type of variability does not guarantee the survival of the organism, but ensures the survival of the species in constantly changing environmental conditions. Indefinite variability is necessary for humans as a breeding tool. It contributes to the natural and artificial origin of new taxa. This is why uncertain variability is the basis of evolution.
