The Significance of Spontaneity Mutations and Its Sources

Spontaneity of Mutations

Evolution refers to the continuous and gradual process of change that occurs over a period of time. During evolution, characteristics of living organisms undergo changes and lead to the formation of new species. Scientists have predicted that the earth is around 4.6 billion years old.

Around 3 billion years ago, the first life on earth appeared. These were tiny unicellular prokaryotes. Around 2 billion years ago, these tiny prokaryotic cells evolved into larger cells that contained a nucleus. Over the course of evolution, tiny prokaryotic cells eventually grew into larger cells and transformed into organelles (example: mitochondria).

Multicellular organisms began to evolve about a billion years ago. It is also anticipated that various animals and plants have been evolving for the past 500 million years.

History of Evolutionary Thoughts

It is anticipated that the emergence of thoughts about the process of evolution of species began during the fourth century BC. Several theories of evolution have been proposed by various scientists. Most importantly, Greek philosophers Plato and Aristotle provided their views on the evolution of species on Earth.

They believed that each organism on earth had been created in its present form, and they remain unchanged. Various evolutionary theories have been proposed by different scientists at different time periods. French biologist Jean Baptiste Lamarck (1744-1829), has proposed that living things could transfer the acquired traits to their offspring.

Later, this idea was opposed by biologists. Darwinism is the most widely accepted theory of biological evolution. It was proposed by Charles Darwin (1809 – 1882), the British naturalist.

Mutations and Evolution

The word ‘mutation’ has been derived from the Latin word “mutare” (meaning: to change). Mutation refers to sudden changes that occur in the DNA sequence (genetic material) of an organism. These changes are inheritable, and they could affect the phenotype of an organism. In nature, mutation is considered to be an important biological process.

Mutation can produce useful or harmful effects. They act as an important source of genetic variation. Mutation of DNA sequence leads to the formation of new alleles. Mutations are very important factors in evolution. They are the major cause of diversity among organisms.

Types of Mutations – Based on Mode of Origin

Based on the mode of origin, mutations could be broadly classified into:

1. Spontaneous Mutations
2. Induced Mutations

Spontaneous Mutations:

Spontaneous mutations are also known as background mutations. Spontaneous mutations are natural and occur suddenly without any known reasons. Replication errors, metabolic errors, or development errors are considered to be the causatives of spontaneous mutations. Naturally occurring spontaneous mutations lead to variations in species.

In a natural environment, ultraviolet radiation from sunlight acts as a mutagen that causes spontaneous mutation. All types of point mutations (SNP – Single Nucleotide Polymorphism) are examples of spontaneous mutations.

Example: Sickle cell anemia in human

Spontaneous mutations result in several changes in the phenotypic characteristics of an organism.

Induced Mutations:

Induced mutations occur in the presence of known mutagens. These mutations are purposefully induced by certain external mutagens. When living organisms are exposed to abnormal artificial environmental factors like radiation, certain chemicals, or certain physical conditions, mutations get induced in them.

Example: Several types of cancer are caused by prolonged exposure to radiation.

Sources of Spontaneous Mutations

The following are the major sources that cause spontaneous mutations:

1. DNA replication errors
2. Spontaneous lesions
3. Oxidative damage
4. Transposons

DNA Replication Errors:

Errors that may happen during the replication of DNA are referred to as replication errors. The most common type of replication errors are—insertion, deletion, and substitution of bases.

Spontaneous Lesions

Spontaneous lesion refers to DNA damage that occurs naturally. Depurination and deamination are the most frequently observed spontaneous lesions.

Oxidative Damage

An increased amount of free radicals are formed due to chemical substances, radiations or cellular respiration. Increased concentration of these free radicals causes oxidative damage to DNA which in turn results in spontaneous mutations.

Transposons

Transposons act as mutagens that cause spontaneous mutations. Insertion of a transposon into any segment of a functional gene results in an alteration of the gene function.