(GIST OF SCIENCE REPORTER) Beneficial Gene Mutations
Beneficial Gene Mutations
The words ‘gene mutation’ often ring alarm bells. This is because gene mutations are popularly associated with many debilitating and life-threatening diseases. So, as a concept, ‘beneficial mutations’ are hard to believe. But beneficial mutations do occur in all living beings, including humans. Many people carry such mutations, though they may be unaware. And scientists are studying them to develop super drugs for diseases that plague humans.
Mutations are defined as alterations in the DNA sequence or the genetic code. Mutations can occur in many ways: change of a single base from one form to another (point mutations), deletions or insertions of one or more bases (frameshift mutations), and structural and numerical changes in the chromosomes which contain the genes (chromosomal
If mutations occur in germ cells, they may be passed on to the offspring. This means every cell in the offspring carries this mutation. If only one of the parents had a mutation in a gene, then the offspring will have one mutated copy of the gene, the other copy being normal. If both the parents carried a mutation in the same gene, then the offspring will have both copies mutated.
Mutations are caused by some type of errors that occur during natural biochemical processes such as DNA duplication during cell division. External agents like chemical pollutants, UV and X-radiations can also cause mutations. Though cells have an extensive network of DNA repair systems to address such situations, some mutations do escape. Geneticists say that we are all born with some mutations inherited from our parents. In addition, we may also acquire mutations during our lifetime.
Majority of the mutations are known to be neutral in the sense that they do not produce any discernible effects; they remain undetected unless genetically analysed. Some mutations are detrimental and cause diseases such as cystic fibrosis, sickle cell anaemia, Tay-Sachs disease, phenylketonuria, colour-blindness, and a few others. Some forms of cancers are also due to inherited mutations.
However, mutations can also improve an existing useful function (gain-of-function mutations), or turn off functions that become pathological (loss-of-function mutations) and thus can be beneficial to the individual inheriting them. These mutations produce characteristics that enable the individual to better adapt to a changing environment. Hence, they are passed on to the offspring at an increased rate by natural selection, which at the same time weeds out the deleterious ones.
Now, how are beneficial mutations detected?
Geneticists examine sick people genetically to determine the cause for their sickness. For example, sickle cell anaemia is found to be the result of a point mutation in which just one base in the DNA sequence for the gene that codes for a sub-unit of haemoglobin has been changed. Because of this small change, the structure of the haemoglobin molecule, which is responsible for carrying oxygen in the blood, changes shape – instead of being round, it takes a curved shape like a sickle.
A sickle-shaped haemoglobin molecule is less efficient in carrying oxygen and also blocks the flow of blood in the arteries, leading to the disease. Likewise, genetic causes of several other diseases like coronary artery diseases including heart attacks, Type 2 diabetes, Parkinson’s disease, Alzheimer’s dementia, etc. are now well established. Many of these diseases are caused by mutations in not just one gene but in many coordinating genes and also carry several risk factors like obesity, age, lifestyle, etc.
Geneticists are now looking at the elderly population, who in spite of having some risk factors are free from some of these chronic diseases. What makes them so? It is generally presumed that such people are not obese, have perfect genome, no disease-causing mutations, follow healthy lifestyle practices like regular exercise, non-smoking and vegetarianism.