Variations in organisms occur by different mechanisms of genetic recombinations and genetic mutations. These variations make natural selection possible. And natural selection acts over many generations. It can increase the proportion of mutants in the population.
Most of the variations are produced by the environment. Thus, environment has a great role in affecting gene expression. In gametes, crossing over plays the role for recombinants. These produce variations.
If variations are positive, they are supported by nature. And if variations or mutations are harmful, they are eliminated. Hence, variation leads to evolution.
What is Variation?
Genetic variation is necessary to the processes of natural selection and biological evolution. The genetic variations that occur in a population occur by chance, however, the process of natural selection does not. Variation means the distinctions (morphological, physiological, cytological, and behaviouristic) among the individuals of the same species and the offspring of the same parents.
Variation is essential in the process of evolution of a species, as genetic diversity is an aspect enabling natural selection to occur. That is, particular variants are selected for and against based on the environment. Different versions of a gene (or variations) that are present within the population are called alleles.
Causes of Variation
A mutation is a change in the DNA sequence. These variations in gene series can often be useful to an organism. Most mutations that lead to hereditary variation produce traits that provide neither an advantage nor disadvantage. Anomalies lead to hereditary variation by altering genes and alleles in a population.
Likewise called gene migration, gene flow presents new genes into a population as organisms move into a new environment. New gene combinations are made possible by the accessibility of new alleles in the gene pool. Gene frequencies might also be changed by the migration of organisms in or out of a population.
Recombinations in Sexual Reproduction
Sexual reproduction promotes hereditary variation by producing different gene combinations. Meiosis is the process by which sex cells or gametes are created. The genetic recombination of genes also occurs during crossing over or the switching of gene sections in homologous chromosomes during meiosis.
Types of Variations
Somatic or Somatogenic Variations:
The variations affect the somatic or body cells of the organisms. They are likewise called adaptations or acquired characters since they are acquired by an individual during its life time. However, these are non-inheritable. They are triggered by three elements– environment, usage, and disuse of organs, and mindful efforts.
- Environmental Factors:
The environmental elements are medium, light, temperature, nutrition, wind, supply of water, and so on. The ecological factors cause only slight adjustments in animals but in plants, the modifications are much more conspicuous.
- Use and Disuse of Organs
This is mainly observed in higher animals. The organ which is put to constant use establishes more while the organ less pre-owned develops a little bit. For example, the blacksmith developing a larger bicep in the arm that works the hammer.
- Conscious Efforts:
Variations due to mindful efforts are observed only in those animals which have intelligence. Getting an education, training of some pets, etc. are some of the examples of conscious efforts.
Germinal or Blastogenic Variations
They are produced in the cells of an organism and are inheritable. They might be already present in forefathers or may be formed unexpectedly. Appropriately, the germinal variations are of two types, continuous and discontinuous.
- Continuous variation
This explains variation in which lots of alleles have little effect on the phenotype. There is no clear separation into unique categories, as measurements are on a continuous scale. Human height is an example of continuous variation. It varies from that of the fastest individual on the planet to that of the tallest person. Any height is possible in between these ranges. So, it is a continuous variation. For any species, a characteristic that changes slowly over a variety of ranges shows continuous variation. Examples of such attributes are:
This explains variation in which various alleles of one gene have a large result on the phenotype of the organism. With this type of variation, individuals can be grouped into distinct classes. A characteristic of any species with only a minimal variety of possible ranges shows alternate variation. The human blood group is an example of discontinuous variation. In the ABO blood group system, only four blood groups are possible (A, B, AB, or O). There are no ranges in between, so this is a discontinuous variation.
Here are some examples:
- blood group
- colors of birds within species
The effect of variation
With altering, allele frequencies come altering genotype and phenotype frequencies. Different genotypes can be associated (discreetly or dramatically) with positive or negative effects on fitness because of the environment. For that reason, a few of these phenotypes/genotypes are favored, and these individuals can reach reproductive age and pass down their genetic information, biasing the population towards a specific phenotype, and changing allele frequencies in the gene pool.