Mutation

Explanation

A genetic mutation is the permanent change or alteration in the DNA sequence of an organism. Mutation usually happens when the DNA gets damaged by environmental factors like exposure to ionizing radiation, where the affected cells reach an irreversible state with a permanently altered DNA sequence. Mutation can pass on to new cells through mitosis, where the DNA replication process causes them to inherit the damaged genes. As the DNA sequence is permanently altered, the resulting proteins from the codons will be different too. This may or may not be dangerous, depending on the significance of the protein function in the organism. For example, in humans, when the genes that are responsible for cell growth called oncogenes mutate, the cells start proliferating, resulting in a severe condition called cancer. Well known forms of this mutation in humans are skin cancer and lung cancer, where the exposure to UV rays alters the DNA in the skin cells, and exposure to tobacco smoke alters the DNA in the lung cells. Mutations generally occur due to the substitution, deletion, and insertion of single base pairs, where the modification leads to mutations like frameshift mutation and other types of point mutations.

When the essential genes of a cell are damaged, the cell usually tries to repair the damaged part of the DNA with several repair mechanisms. When the errors are not repaired in time during the DNA repair process, mutation succeeds and spreads through replication. In some cases, mutations are induced by the repair process itself. As dangerous as it sounds, mutation can also be beneficial in many cases and is an essential part of evolution. Throughout the life of a cell, DNA can undergo mutation several million times, and most are repaired at the same rate.

Frequently Asked Questions

How are mutations beneficial?

As mentioned earlier, some mutations turn out to be beneficial for the organism involved. This may be due to the external factors influencing it. A common type of beneficial mutation found in humans is the mutation of the genes that are responsible for the coding of the protein called haemoglobin. In countries like Burkina Faso, the natural selection amplified haemoglobin mutations turned out to be beneficial for the humans as they resisted the parasite Plasmodium falciparum that caused malaria. Therefore, beneficial mutations are significant in a way that ensures the survival of the organisms as a community, adapting to their environment.

As with many evolutionary 'solutions', this one comes with a trade-off. While these mutations (shown as the allele 'h' in this paragraph) enhance resistance to sickle cell anemia, an individual with TWO copies of the mutation (hh) is extremely anemic, and without modern medicine was doomed to die very young. For this reason, sickle cell alleles are common in populations where malaria is prevalent because the heterozygotes (H/h) have enhanced resistance to malaria with only very minor anemia. 'Wild type' (HH) individuals are highly susceptible to malaria. In populations without malaria, there is no advantage for Hh individuals, so the deaths of hh individuals removes the h allele from the population.

What are the differences between DNA damage and DNA mutation?

A DNA damage is an error in the base pairs of a single DNA strand that can be corrected or repaired by the enzymes by using the complementary pair as a template. But when both pairs are affected, or a template with the damaged sequence is selected for the replication process, DNA mutation occurs and causes a permanent change in the genome of the organism.

Can mutations be reversed?

In the recent years, gene therapy is used to modify the DNA of the human cells to treat various diseases caused by mutations. In general, a virus is genetically engineered to deliver the corrected DNA into the chromosome inside a target cell's nucleus. More recent developments from studying the CRISPR system allow us to edit and alter the gene in a DNA directly. A similar mutation that happens in DNA that corrects a previous point mutation is known as compensatory mutation. Compensatory mutations occur at a particular point on the DNA sequences such that it nulls or reverses the effect of the previous mutation.