## Mutations and their effects on organisms

As mentioned previously, DNA damage, if not repaired, can lead to mutations, which is a change in the nucleotide sequence of DNA. The effect of the mutation then depends on several factors: If the mutation originated in a non-coding region (outside the region of a gene that codes for a protein) its effect is usually not present. Such a mutation can only be detected by DNA sequencing. However, if it has arisen in the gene region, its effect may still be seen, depending on whether it is a substitution or a displacement mutation (Figure 5.4).

The effect of the mutation also depends on the cell in which the mutation arose. If it originated in a somatic (body) cell, the mutation cannot be passed onto future generations, and manifests itself only in that cell and its daughter cells. Thus, such a mutation affects only the organism in which the cell is located. In contrast, a mutation in a germ cell (a sperm or egg) is passed onto the next generation and will affect the offspring. An example of such a mutation is the mutation causing haemophilia that originated in a member of the English royal family, Queen Victoria, and was passed down through generations.

The term "mutation" has a negative connotation for most people. However, mutations can also lead to the emergence of new traits that are beneficial to humans, especially when it comes to food, which can give fruit and vegetables new size, taste or colour. An example of this is the somatic mutation in apples that led to the creation of the ‘Delicious’ variety, which can be red or yellow in colour. The possibility of vegetative propagation of plants makes it possible to preserve and use this mutation. The mutation that leads to sickle cell anaemia also cannot be considered only a negative mutation, since people who are heterozygous for the mutation (i.e., are carriers of the disease) have resistance to malaria (since the mutant red blood cells cannot be attacked by the Plasmodium parasite that causes this disease. You can read more about this in Chapter 11 - Plants as inspiration in biomedicine. For this reason, sickle cell anaemia is very common in some populations, especially in areas heavily affected by malaria.

So far, we have only talked about mutations that occur at the level of one or more nucleotides. However, a large group of mutations consist of changes at the level of the chromosomes, where one or more can be multiplied (so-called chromosomal aberrations). These changes occur mainly as a result of cell division disorders, when chromosomes are incorrectly distributed into daughter cells. The result is germ cells with an extra chromosome or, conversely, a chromosome missing from the germ cell. The likelihood of incorrect chromosome division increases with the age of the mother, since germ cell embryos are formed during intrauterine development of females. However, in humans only trisomies of some chromosomes (13, 18, 21 and X) are known, as others have such severe effects on the organism that foetuses with such anomalies die during embryonic development. A well-known example of duplication of a chromosome in humans is trisomy of chromosome 21, known as Down’s Syndrome.

In addition to the change in the number of individual chromosomes, the duplication of entire sets of chromosomes (polyploidy) can also occur under certain circumstances. This occurs mainly in plants and can also be achieved specifically through breeding. One of the consequences of polyploidy is an increase in the volume of the cell and thus of the entire organism, which is why polyploid species are often used as food in agriculture (e.g. wheat, banana, etc.). In animals, polyploidy occurs less frequently however examples can be found in some amphibians and fish.