Classification of elementary evolutionary factors
Evolutionary factors are traditionally divided into two large groups depending on their functions and impact on the population.
1. Main EEFs Their main function is to ensure the emergence of completely new alleles, chromosomes, and entire chromosome sets. This group includes:
- Mutation process.
- Population waves.
- Isolation.
- Natural selection.
2. Additional EEFs These processes do not create fundamentally new material, but actively change the frequencies of existing alleles and the general genetic structure of the population. Phenomena such as the Baldwin effect and the bottleneck effect are associated with the action of these factors. This group includes:
- Migration (also known as gene flow).
- Meiotic drive and other accompanying mechanisms.
Mutations and genetic environment
Organisms in which an arising mutation manifests phenotypically are called mutants. At the same time, the nature of its manifestation strongly depends on the specific group of organisms.
An important contribution to the understanding of these processes was made by Ronald Fisher, who published the work "The Genetical Theory of Natural Selection" in 1930. According to his theory, the external manifestation of any gene directly depends on its genetic environment. This environment is formed due to complex gene interactions of the pleiotropy and polygeny type.
A key role in this process is played by recombination. It creates fundamentally new gene combinations, forming an environment that allows a hidden mutation to finally manifest itself in the phenotype. Only after this does the mutation fall under the action of natural selection.
The result of the action of selection boils down to two directions:
- Elimination of those gene combinations that make life or reproduction difficult for the individual.
- Preservation of selectively neutral and advantageous combinations, which are subsequently subjected to reproduction and constant testing by environmental conditions.
Types of carriers and germline mutations
In population genetics, several important concepts related to the manifestation of traits are distinguished:
- Mutation carriers are organisms that are heterozygous for a recessive mutant allele. Their main feature is that the mutation does not manifest itself in their phenotype at all, and consequently, is not subjected to the pressure of natural selection.
- Selectively neutral mutations are genetic changes that are not subject to any noticeable action of selection.
Important rule: when constructing evolutionary models, researchers consider exclusively germline mutations (arising in germ cells). Genetic mosaics are not taken into account in evolutionary calculations.
Interrelation of population genetics and the environment with examples
The action of evolutionary factors can be traced at the intersection of population genetics and immunity. For example, there is a proven correlation between a person's blood type and their resistance to infections.
Historically, people with a certain blood type could not produce a sufficient amount of anti-plague antibodies, which is why they died. A striking example of the work of selection is the population of Native Americans: they were practically unaffected by plague, and to date, the frequency of the $I^0$ allele in their population is more than 90%.
Another powerful evolutionary factor is population waves (demographic explosions). For example, the Siberian moth (Dendrolimus sibiricus) is capable of abruptly increasing its population size by 12 million times. In the course of its development, it goes through classical stages: larva, pupa, and adult insect.
Briefly: answers to topical questions
What is the essence of the bottleneck effect in population genetics?
The bottleneck effect consists in a sharp reduction in population size due to various causes. This phenomenon belongs to additional elementary evolutionary factors that randomly change allele frequencies and genetic structure.
Consequences of the effect:
- Decrease in genetic diversity.
- Depletion of the gene pool.
During the subsequent recovery of the population size, gene and allele frequencies turn out to be altered. They no longer correspond to the genetic parameters of the original population.
What is the Baldwin effect in the context of evolutionary changes?
The Baldwin effect represents the process of consolidation of adaptations and the creation of phenotypic variability for natural selection based on epigenetic mechanisms. Changes in gene expression arising under the influence of the environment can be transmitted to a number of generations.
Example of the mechanism at the symbiotic level:
- Behavioral shift — search for new food sources (an analogue of destabilization).
- Change in selection — a new diet changes the selection pressure on the organism and microbiome.
- Assimilation — adaptation is consolidated in the genome of the "superorganism".
What are the mechanisms of occurrence of meiotic drive?
The mechanism of meiotic drive consists in the deviation of the ratio of gametes produced by a heterozygote from standard Mendelian segregation in favor of one of the alleles.
Stages of the process using oogenesis as an example:
- A mutant allele arises in the population alongside the wild-type allele.
- During meiosis in females, only one egg cell is formed from four haploid cells, while three polar bodies die.
- The mutant allele enters the egg cell more often than the wild-type one.
As a result, positive selection pressure arises regarding the mutant allele, which leads to its fixation in the population.
What causes the formation of genetic mosaics in living organisms?
In the cited sources, mosaicism is described as a result of chromosome nondisjunction at early stages of zygote division — using the mosaic variant of Down syndrome as an example.
In evolutionary models, genetic mosaics are not taken into account, since only germline mutations are considered.
For the mosaic variant of Down syndrome, it is indicated that the intellectual deficit is significantly less pronounced. When embryos with mosaicism are detected during preimplantation genetic testing, a consultation with a medical geneticist is necessary to resolve the issue of the feasibility of transferring such an embryo.
To memorize the four main evolutionary factors (Mutations, Isolation, Waves, Selection), use the phrase: "World Changes Arise Through Selection."
Class and exam questions
What are elementary evolutionary factors?
These are probabilistic (stochastic) processes occurring within populations. They are the primary sources of intra-population variability.
What is the core of Ronald Fisher's theory?
Fisher proved that gene expression depends on its genetic environment. Recombination creates new gene combinations, allowing a mutation to manifest in the phenotype and fall under natural selection.
Why do mutation carriers escape natural selection?
Carriers are heterozygous for a recessive allele. Because of this, the mutation does not manifest in their phenotype, and selection simply cannot affect it.
Are genetic mosaics accounted for in evolution?
No, in classical evolutionary models, only germline mutations transmitted to offspring are taken into account.
What else to study on this topic
- Recombination mechanisms and the formation of the genetic environment
- Gene interaction: pleiotropy and polygeny
- Baldwin effect and the bottleneck effect
- Meiotic drive and migration as evolutionary factors
- Population wave dynamics using the example of Dendrolimus sibiricus
Master the entire topic in the "Biology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Elementary evolutionary factors" and 3,793 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 130 video lessons in the subject
Other topics in «Elementary evolutionary factors»
Free video lessons: BiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.