In my opinion, when it comes to the general public, mutations often have a negative connotation as they are usually being associated with genetic diseases and microbial and viral outbreaks. However, mutations are a source of change in living organisms. On a larger time scale, cumulative changes in the genetic material lead to the process of speciation and are one of the drivers of evolution.
Concept of Mutations
The concept of mutation has been popularized in cartoons and movies, just like cloning. For example, the entire film series X-Men has been based on the concept of genetic mutations. But, mutations, per se, don’t create dramatic changes, as is seen in such films. In nature, they are random. These random changes are usually small because complex organisms can’t undertake major genetic changes. Living organisms are intricate beings that have been perfectly balanced throughout millions of years of evolution. This balance is largely encoded by our genes. Therefore, even the smallest qualitative or quantitative changes can have significant consequences on the being that is the carrier of a particular mutation. There are many ways in which mutations can be categorized. The classification that will be used in this text is that mutations can be either germinal or somatic.
Somatic mutations are common and they happen in every living being. Our cells duplicate and split on a daily basis to maintain our tissues and organs, even when we’re no longer physically growing. In this process, DNA replicates and many safety mechanisms make sure that DNA is being correctly reproduced. However, sometimes these mechanisms fail and a cell with changes in genetic material is being produced. Even when this happens, there are special cells in our immune system that can recognize and terminate them. Unfortunately, in some cases, this isn’t enough. Consequently, the mutated cell survives and continues reproducing which leads to the creation of a mutated cell line. Usually, these cell lines are, what we colloquially call, cancer. Cancer is a very serious disease because mutations that lead to it usually enhance its ability to reproduce, e.g. mutations in one of the components of signal pathways that leads to overexpression of growth factors and receptors. As these cells reproduce, they mutate further because the repair system is impaired as well. On top of that, they use the exact same pathways, molecules and resources as the entire organism which makes them very difficult to target by therapy. Fortunately, such changes aren’t passed down to the offspring.
On the other hand, germinal changes are the ones that are very interesting to evolutionists. They happen in the reproductive cell line which means that they are being passed down on the offspring and further into the population. However, these changes still have to be minor to produce capable progeny. As we know, major abnormalities in genetic material lead to pregnancy loss, stillbirth, or offspring with significant disabilities. Such major changes usually refer to chromosomal abnormalities, but even small mutations in coding regions can have the same effect. However, sometimes even chromosomal abnormalities can lead to speciation in isolated populations. For example, translocations and inversions are sometimes evident when you compare karyotypes of evolutionary close species. Nevertheless, these events are rare. The most common changes in populations are point mutations. They lead to the change of one base pair in the code which doesn’t have to have any effect on the protein sequence due to the redundancy of the genetic code. The type of point mutation that usually leads to detrimental effects is frameshift when a base is accidentally added to or deleted from the reading frame. This type of change usually leads to the complete malfunction of a gene.
Mutations In The Context Of Evolution
So, when it has been put like this, you may wonder, what kind of mutations drive evolution? It seems like most of the changes are deleterious for living beings. Well, that is true and most mutations are harmful when it comes to their effect on fitness. A small amount of mutations belongs to beneficial and neutral ones. Since mutations are a random process, beneficial changes are even rarer than neutral ones. I also have to add that the effect of these mutations depends on the environment. For example, polar bears are white which helps them camouflage in the Arctic Circle, but this white colour would be a disadvantage in a forest with a temperate climate. Similarly, neutral mutations might become beneficial in a change of surroundings.
The interaction of external factors and genetic material is very complex and it has led to different evolutionary theories. The most famous is the theory of natural selection proposed by Darwin saying that beneficial mutations are the drivers of evolution. This theory proposes that an individual with a beneficial change will survive and/or reproduce more efficiently. Therefore, it would produce more offspring that would pass on this mutation. In this way, the most common changes in the population would be beneficial. However, molecular evolutionists disagreed. Motoo Kimura has proposed the theory of neutral selection saying the most common mutations are neutral and selectively neutral ones. Molecular evolutionists and population geneticist propose that neutral changes happen more often and that their destiny is decided by the random process of genetic drift. This theory doesn’t negate Darwin’s, it supports its emphasis on phenotype, but it adds that these positive changes are rare. Development in molecular genetics has given insight into the hidden/neutral diversity of the genetic code.