Our body is a true miracle. However, it can only function if the proteins produced on the basis of the DNA do not have any defects and fulfill their tasks as workers and building materials of the cells as planned. But sometimes misspellings occur in DNA. These errors are called mutations.
Defects can affect single bases, gene segments or even whole sets of chromosomes
-Damage can occur in different places in the. If they don’t fix them, mutations occur:
- Genome mutations refer to entire chromosomes or sets of chromosomes that have been multiplied or lost. You may be familiar with Down syndrome, also called. In these people, the 21. not in duplicate, as is normal, but in triplicate. Genome mutations are also known in plants in agriculture, but there they are often deliberately triggered or bred. With the multiplication of the entire set of chromosomes, wild plants became larger and more vigorous cultivated plants. The garden strawberry, for example, has roughly the same chromosomes as the wild strawberry, but in quadruplicate! But there are also wild plants that naturally have a multiple set of chromosomes.
- Chromosomal mutations are changes in individual chromosomes. For example, pieces of chromosomes may be lost or duplicated. Sometimes a part of a chromosome turns upside down or two chromosomes merge into one large chromosome. One example of a chromosomal mutation is cat cry syndrome (the disease is called this because affected infants often cry like cats due to a malformation of the larynx), in which part of chromosome 5 is missing.
- Gene mutations occur when the base sequence (i.e. the ) of individual genes is altered. One or more may be lost, multiplied, or “sneak” into a series of letters. This leads to a change in the reading frame of the genetic code, so that the wrong amino acids are used for protein construction. This usually has bad consequences for the body. An example of this is cystic fibrosis: on chromosome 7, some bases have been lost, so that the body now produces a protein that is no longer functional – viscous mucus forms in the lungs, which severely impairs the function of the organ.
- Gene mutations can also occur when one base is replaced by another (e.g.B. an adenine for a cytosine). This can lead to the insertion of a single wrong one in the produced one. Often this is harmless, because certain amino acids can be exchanged for others without negative consequences. Sometimes, however, the protein produced is altered, as for example in sickle cell disease. In this disease, due to a point mutation glutamate → valine, the protein is altered so that the red blood cells look sickle-shaped. In homozygous carriers, where both of the gene are altered, this leads to life-threatening circulatory disorders, while in heterozygous carriers the disease produces no or much weaker symptoms. Interestingly, sickle cell disease is particularly widespread in Africa and the Middle East; the reason is thought to be that it protects heterozygous carriers against malaria to a certain extent. Apparently, in malaria areas, this gene modification is such a great advantage for heterozygotes that it could be established in the population, although it is a serious disadvantage for homozygotes.
Only defects in the germ cells are inherited
One in a cell is passed on to the daughter cells. If only affected by the mutation, the person gets sick, but does not pass the mutation on to his or her offspring. For example, tumors arise from defective cells that proliferate without control.
However, if (i.e. sperm or egg cells) carry a mutation, this is passed on from parent to child during reproduction. In cystic fibrosis, the child must have the corresponding mutation from both parents for the disease to occur (recessive ). For other diseases, it is sufficient if only one parent passes on the mutation (dominant inherited disease).
Mutations do not always have to be bad
However, unrepaired mutations do not always have to have dire consequences. Many mutations happen in areas of DNA that are irrelevant to protein production and thus have no consequences. In addition, our body has two copies of each chromosome (one from the mother and one from the father). If there is a mutation on one of them, often the second, healthy chromosome can compensate for the error. In the next generation, of course, there is a risk of inheriting the mutation twice (once from the mother and once from the father).
Last but not least: The fact that spontaneous changes occur in the genetic material is an important mechanism of the ! For if a living being suddenly becomes more successful than its fellow species through a mutation, it has better chances of survival and produces more offspring. By passing on positive mutations to offspring, better-adapted populations – or even new species – are created.