Mutations of our genome
Mutations of one’s own genetic information can have far-reaching consequences for the organism. A strict distinction must be made between “norm deviations” that can be passed on to the next generation and those that exist only in one or more selected cells. In genetics, one differentiates between “germline mutations” and “somatic mutations”.
Cut to the chase:
- Mutations of the genome can be passed on to the next generation, provided that this change also occurs in germ cells.
- One differentiates genome mutations, chromosome mutations and gene mutations. These types of mutations affect both germ cells and “normal” cells.
- Mutations of the genome are “natural” and for the time being not a problem, because some defense mechanisms are available. Up to momentous mutations, a large number of such changes must have occurred in the correct sections of the DNA. Especially mutation of so called protooncogenes to oncogenes can cause cancer.
- The causes of mutations vary greatly. Especially reactive chemical compounds occurring in our own metabolism damage our genetics.
- Everyone can take care to counteract mutations: avoid mutagenic substances or pathogens and be careful with UV radiation.
Mutations in germ cells can be passed on
Whether a mutation of the genome can be passed on to another generation depends primarily on the cell types involved. For a mutation to be passed on to one’s own children, it requires a mutation of genetic information in our germ cells (egg and sperm). If a mutation occurs in a simple body cell, for example in a liver cell, the changes and consequences are limited to the affected organism. However, both germline mutations and somatic mutations alter the genome in detail.
There are three types of DNA alteration
Our genetics can change in different ways. Here, one differentiates technically between genome mutations, chromosome mutations and gene mutations. In the context of genome mutations, numerical deviations in the total number of chromosomes can occur. Usually, each body cell has 46 chromosomes. Regarding genomic mutations, there can be deviations upwards or downwards. In the case of chromosomal mutations, on the other hand, there is a risk of major structural changes in individual chromosomes. Finally, gene mutations are the smallest changes on a chromosome, such as the deviation of individual nucleotides or nucleotide regions.
We are not masters of all mutations
Unfortunately, it is not possible to stop or prevent all causes that lead to mutations. Mutations, especially in the germ line, are strictly speaking part of evolution and have ensured over time that the overall construct Homo sapiens functions down to the smallest detail. At the same time, it must be noted that in the course of evolution, mechanisms have emerged that can decisively counteract these mutations and gene changes. These “genome guardians” include repair mechanisms in particular, but also other processes such as programmed cell death.
Metabolic errors cause mutations
Looking at the causes of mutations, it is striking that the majority of all mutations occur in the metabolism of the DNA itself. From a simple decay of DNA molecules to mutagenic chemicals to ionizing radiation or unexplained spontaneous mutations — the causes are manifold. Mutagenic chemicals are often reactive compounds produced in our own metabolism. Exogenously, such gene-modifying substances can be absorbed orally through inhalation or skin contact.
Usually, the resulting damage is compensated by our own system. However, some of these mutations slip through — they escape our defense systems. The establishment of new variants in the genome is also a normal process. A human collects about 14 new mutations in a blood stem cell every year. Most of these mutations are harmless. Before a mutation leads to relevant changes within a cell, numerous factors must be involved. In particular, the number of mutations, the affected genes and the working strength of our defense mechanisms play a role.
The causes of mutations vary greatly. Above all, reactive chemical compounds produced in our own metabolism damage our genetics.
Possible consequences of mutations
If relevant mutations occur, such as a numerical deviation of the fixed chromosome set, a cell is usually not viable and is eliminated. However, if such a process occurs in germ cells, abnormal sets of chromosomes may result in subsequent fertilization (such as trisomy 21). Mutations of individual gene segments can lead to an ineffectiveness of this gene and thus its function.
It is problematic when relevant mutations occur in so-called protooncogenes. These genes are able to “switch” to a so-called oncogene when altered and to promote survival and growth of the cell in a malignant sense through defective gene products. In the worst case, the cell degenerates and a tumor develops through proliferation. In addition, “loss of function”, i.e. a loss of function of the gene, can lead to specific disease patterns. If individual genes are already unusable in germ cells, so-called hereditary diseases occur in which the child is born with individual defects.
Influence of lifestyle
Even though mutations are natural, we can trigger or promote them through our lifestyle. For example, mutagenic substances (such as pesticides) and ionizing radiation (especially UV light) should be avoided, and care should be taken to maintain adequate hygiene, since infections with various microorganisms (such as HPV) in particular have mutagenic properties. One of the best-known measures is the intake of radical scavengers (such as selenium) to neutralize harmful free radicals produced during metabolism.
Text-Sources:
(1) Murken et al., Humangenetik, 9. Auflage, 2017
(2) Nordheim und Knippers, Molekulare Genetik, 11. Auflage, 2018
(3) Munk, Genetik, 2. Auflage, 2017
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