What is Evolution?

Evolution is known as continuous changes that occur to adjust organisms in their changing environment over many generations. Various theories have been proposed to illustrate the origin of life and organic evolution. The most accepted one is the theory of natural selection by Charles Darwin. According to his postulate, organisms undergo a struggle for existence due to overproduction. To survive in nature, they acquire variations. The inheritable variations are selected by nature, and it leads to the survival of the fittest.

What is Evolutionary Genetics?

Evolutionary genetics is the branch of biology that involves a detailed study of evolution in terms of genetic variation and traits. The changes that occurred millions of years due to evolution are viewed by considering the evolution of genetic material. It deals with the study of the genome sequence of population, speciation, and adaptation of organisms. The evolutionary forces such as natural selection, mutation, and genetic drift bring changes in the environment and competition to give rise to new variations in the organism.

History of Evolutionary Genetics

Evolutionary genetics is studied as a branch of biology. It has emerged from integrating the theory of genetics proposed by Gregor Mendel and Darwin's theory of natural selection. Julian Huxley, in 1949, combined these unrelated topics and called it modern synthesis; it also comprised paleontology, ecology, and molecular biology. The theoretical works conducted by R.A Fisher, J.B.S Haldane, and H.J Muller inspired forming modern synthesis. E.B Ford invented the field of ecological genetics and studied natural selection and variations in population.

Evolution of Genome structure

The new varieties of the genome are the result of recombination and mutation in genes. The following stages give a detailed explanation of the evolution of genes in organisms.

• Genomes of primitive earth: The early condition of the earth was not suitable for living entities. The abiogenesis theory and chemosynthetic theory from Oparin and Haldane suggest that organisms were evolved from inorganic substances of the primitive earth. The molecules of life, such as amino acids (alanine, glycine, and valine), were found in the experiments of Miller and Urey. So, it is believed that such amino acids went through various reactions, and units of genomes, including purines, pyrimidines, and sugars, were formed.
• RNA-centered life: Ribonucleic acid (RNA) was the genetic material before the formation of deoxyribonucleic acid (DNA). RNA stored genetic material, self-replicated, and resulted in more production of cellular organisms. This theory is called the RNA world hypothesis proposed by Carl Woese, Francis Crick, and Leslie Orgel in the 1960s. The RNA came into existence when biomolecules started to accumulate. The operation of natural selection gave rise to a more efficient replicating system. These primitive cells were working with the help of the ribozyme’s catalytic activities.
• Origin of DNA genomes: DNA genomes were originated with the evolution of protein enzymes. They replaced the RNA world eventually. These cells were called genomes or protogenomes. The deoxyribonucleotide became dominant over ribonucleotides. Thymine enabled the DNA to attain its stable form. DNA also attained a double-stranded structure with the help of its repairing mechanism.
• Prokaryotes: The single-celled organisms were most likely to evolve first on the earth. They were present in the form of biofilms or microbial mats. In the beginning, prokaryotes obtained their energy from hydrothermal vents. They were anaerobic before the great oxygen event. The origin of cyanobacteria in the earth led to the formation of oxygen.
• Eukaryotes: The oxygen molecules started to deposit in the environment, and organisms developed nuclear envelopes to prevent DNA molecule oxidation. The development of the nuclear envelope gave rise to eukaryotic organisms. These organisms represent the complex double-stranded DNA of the present day.

Forces of evolution that act on genes

• Gene flow: Gene flow is the result of the exchange of genes between two different populations. The transfer of alleles from one population to another causes the origin of a new variety of traits. The gene flow depends on the rate of migration of the species.
• Genetic drift: Genetic drift occurs in the population when they are separated or drifted. The random change in alleles causes the formation of new traits or species. In genetic drift, the smaller population always tends to extinct. 
• Mutation: The mutation results from the insertion, deletion, and moving of genes from one sequence to another. The change in genome structure brings new traits to the species. Mutation might cause harmful changes in the organism. The beneficial mutated traits selected through natural selection are passed onto the next generation.
• Natural selection: When organisms adapt new traits, they are favored by nature, and these are inheritable. The force of nature brings changes in the genomes of the organisms. The discontinued variants are considered harmful to the species, and these are not favored by nature, thus are not inherited. 

Speciation in Evolutionary Genetics

Speciation is the development of a population community through an evolutionary process. The formation of complex species is conducted via two modes. Darwin illustrated the importance of natural selection in developing new traits and their role in forming species. Speciation forms both geographically and genetically. 

The geographic model of speciation 

• Allopatric speciation: The formation of new species occurs when the habitat of the living organisms is separated, for example, the formation of mountains. During this condition, the population undergoes genetic drift or mutation and evolves into two different species. Phenotypic or genotypic variation in the organisms separates them as different species. An example of such speciation is found in Darwin's finches.
• Peripatric speciation: This speciation occurs due to habitat destruction, but only a small population gets separated from the main population. It is considered a subcategory of allopatric speciation. This type of species is an example of the founder effect of genetic drift. Their survival rate is less. 
• Parapatric speciation: When partially separated populations inbreed, they show less survival rate due to heterozygosity and limited gene flow. Gradually the natural selection and new recombinants give rise to new species. 
• Sympatric speciation: Sympatric speciation occurs when multiple species originate from a single ancestor, for example, cichlids and rock lizards.

The genetic model of speciation

• Formation of species by polyploidy: The new species formation takes place when inter-related species mate. Recent studies suggest that many of the present-day diploid organisms have polyploid ancestors formed from polyploidization. The successful reproduction and occurrence of the gene pool result in new species. Triploid progenies are formed from the mating of haploid and diploid gametes. The triploid progenies formed are unstable and sterile. These triploid organisms usually show the asexual mode of reproduction and cannot interbreed with their diploid ancestors.
• Hybrid speciation: The recombinant genes produced by the mating of two genes result in both traits. This new trait sometimes emerges as the most potential trait to fit in the environment. Hybrid species generated new species in animals as polyploidy occurs only in plants and lower organisms that reproduce asexually.
• Gene transposition: Theodosius Dobzhansky introduced the gene transposition concept. According to him, when alleles or parts of the chromosomes separate from their original chromosomes, new traits are originated. The changes in the location of genes give rise to the different genome sequences, which results in the birth of new species.

Adaptation in Evolutionary Genetics

The fundamental questions of biology are addressable by the study of adaptation at the molecular level. Organisms eventually develop certain characters for better living in the environment. Adaptations occur to meet the competition of food, shelter, and mates. The adaptation in organisms can occur in various forms. Those forms are as follows: 

• Adaptation from the habitat change: The changes in the environment lead to either genetic change or extinction in organisms. The genetic changes in the organisms help in better adaptation to the new environment. Most of the organisms move to different habitats during this condition, and it is called habitat tracking.
• Genetic change: Organisms change their genome sequence due to mutation. When these genes are inheritable, they are selected by nature and give rise to a new variety of genus or species. Organisms' genetic change always occurs due to the influence of their circumstances. For example,  mutation influences color change due to air pollution in melanic moths or peppered moths. Therefore, radiation and carcinogenic or toxic elements present in the environment cause mutation. Abnormal cell division is another cause. 

• Co-adaptation: Co-adaptation or co-evolution is the result of mutualism or symbiotic relationships between organisms. Two dependent organisms acquire the required characters for their symbiotic relationship. For example, insects have developed pollen baskets for flowers' pollination.
• Mimicry: Various organisms exhibit anti-predator adaption, and this adaptation is called mimicry for better survival. The butterflies of the genus Caligo have an eye-like structure on their wings. These appearances exactly resemble the eyes of an owl. The other examples include the appearance of wasps in honeybees and warning coloration. 

Applications of Evolutionary Genetics

The study of evolution in the perception of genetics, including population genetics and polygenetic analysis, helps to improve human welfare. The molecular-level analysis helps to produce vaccines for various diseases and improve gene therapy and genetic engineering. Evolutionary genetics assist in tracing disease-causing organisms and their destroying mechanism. It is also applicable in treatment studies for bacterial antibiotic resistance, virulence, and many protozoan diseases.

Common Mistakes

Students might get confused about evolutionary genetics and population genetics. Evolutionary genetics represents the evolution of genes over time, whereas population genetics deals with changes of traits within the population. These two topics are studied together to understand the change in gene frequencies and speciation.

Context and Applications

• Bachelor of Science in Biology
• Master of Science in Zoology
• Master of Science in Botany
• Master of Science in Molecular Biology

Related Concepts

• Evolutionary Biology
• Genetics
• Molecular Biology
• Ecology
• Cytogenetics

Practice Problems

Q1: Which of the following is not an evolutionary force?

(a) Mutation

(b) Genetic drift

(c) Equilibrium of population

(d) Natural selection

Correct choice: (c)

Q2: Sympatric speciation occurs when ________.

(a) habit destruct

(b) geographical area separate

(c) inbreed

(d) the origin of multiple species from a single ancestor

Correct choice: (d)

Q3: Which factor of genetics supports evolution?

(a) Genetic variation

(b) Recombination

(c) Somatic mutation

(d) All of the above

Correct Choice: (d)

Q4: The basic molecule of life is ___________.

(a) inorganic molecules

(b) lipids

(c) carbohydrates

(d) proteins

Correct Choice: (d)

Q5: The organisms with nuclear membranes are __________.

(a) eukaryotes

(b) prokaryotes

(c) bacteria

(d) virus

Correct Choice: (a)