When they hear the word mutation, many people probably think first of hideously deformed creatures from horror movies and less of biology. Yet mutations play an important role everywhere in biology: for evolution, the emergence of new species, the emergence of new creatures, and ultimately in the emergence of many diseases. However, mutation takes place on a much smaller scale than in the movies: as a tiny change in a tiny spot of our genetic material in just one cell of our body. Such mutations happen thousands of times a day in our bodies. Therefore, for a mutation to ultimately result in an outwardly visible change, numerous coincidences really do have to come together.
What is mutation?
By definition, a mutation is a permanent change in our genetic material, which is passed on from the once mutated cell to its daughter cells as part of cell division. By definition, a mutation is a permanent change in our genetic material that is passed on from the once-mutated cell to its daughter cells as part of cell division. If this mutation happens in a sperm or egg cell of our germ line, the mutation may be passed on to the offspring and this is called a germ line mutation – creating biological diversity and evolution in the long run, but in the short run, and in the worst case, hereditary diseases. If the mutation happens in every other cell in the body, it is called a somatic mutation – in most cases this cell becomes dysfunctional and is sorted out by the immune system, in the worst case it breaks ranks, divides uncontrollably and becomes a tumor.
Functions and tasks
According to the cause, spontaneous and induced mutations can be distinguished. Spontaneous mutations occur without external cause and quasi constantly in our body. Every second, countless cell divisions take place in the human organism; each time, the DNA, i.e. our genetic material, must be duplicated for this purpose and distributed to the two daughter cells that are formed – it is clear that something goes wrong in the process! Furthermore, bases from the DNA can also spontaneously chemically decay and from the one base suddenly another one is formed, which suddenly results in a completely different information for the reading mechanisms. Induced mutations are caused by external influence and there are many suspects: The mutagenic effect is assured, for example, for radiation and many so-called carcinogenic substances such as nitrosamines from cured meat or benzpyrenes from cigarette smoke. Such induced mutations can probably not be completely prevented in this world, but a whole series of pollutants and risk factors are now known, the avoidance of which can reduce the risk of a mutation developing to a minimal residue:
Do not smoke, do not eat burnt meat, apply sunscreen before sunbathing, take X-rays only if absolutely necessary, protect against radiation at the workplace, etc. – in this way a large part of the mutations can be avoided at the cellular level. In the remaining cases, such a mutation is not a big deal: A large part of our DNA is irrelevant for the transmission of hereditary information anyway – a mutation there does not change the pattern of the read proteins at all. If a site of genetic information that codes for an important protein in cell metabolism does mutate, there are several protective barriers: Among other things, proteins constantly patrol our cells as “guardians of the genetic material”, which recognize mutations and – depending on their extent – either allow them to be repaired directly or, in the case of irreparability, simply initiate controlled cell death. The immune system then simply clears these cells and replaces them with new ones. If this protective mechanism fails and the DNA is finally read incorrectly, in most cases the result is nonsense, the cell becomes non-functional and remains with its nonsense protein until its cell death. Only if, by chance, a mutation at a crucial point results in something “sensible”, i.e. something that functions in whatever way, does this sometimes have major biological effects.
Diseases, ailments and disorders
If the mutated cell is a germ cell, for example, a sperm, and if this sperm should ultimately prevail in the race to fertilize an egg, then every smallest mutation in the genome can have major consequences: A different hair color, a centimeter more height, different intelligence, different interests, a different person – everything is conceivable. In this way, evolution has simply tried out certain human, animal and plant characteristics at random every now and then, and if they proved to be good, they prevailed. Also, every child is not simply the sum of mother and father, but at the same time the product of small mutations, which in turn give rise to completely new characteristics and keep the genetic material surprisingly interesting even within the family line. In addition, today’s medicine is also aware of a large number of defined mutations on certain genes that deviate so far from the human “normal” that they can be called hereditary diseases: In cystic fibrosis, for example, a single gene on chromosome 7 is minimally altered – with maximum effects on the quality of life and life expectancy of those affected. In Down syndrome, on the other hand, the number of chromosomes is mutated – instead of two copies of the 21st chromosome, there are three, which is why the disease is also called trisomy 21. There are many other examples of more severe hereditary diseases, which may also be passed on to the descendants of the affected person. Some of them are also inherited only recessively: this means that in most cases they are masked by a healthy partner chromosome and only appear as a disease when the partner chromosome is also mutated. Genetic diseases in the larger family circle can be an indication of the presence of such hidden mutations and justify a visit to the human geneticist before conceiving a child. Somatic mutations, meanwhile, are of greater relevance to those who are not newborns or parents-to-be: If any body cell mutates (which happens all the time, as I said), with a bit of bad luck it loses control over its cell division as a result. This is how cancer develops. This mutation is then also irreversible and is passed on to all daughter cells, so that these in turn want to continue to divide endlessly without taking into account any necessities or external influences on the part of the rest of the body. The tumor grows and grows – and hopefully is discovered quickly enough, as long as it can still be operated out without major collateral damage and has not yet spread metastases throughout the body.
