How genetically similar are humans

Why do scientists research mice?

In order for an animal to become a model organism for science, it must have several properties: It must be comparatively small and easy to keep. It should also reproduce quickly. Only under these conditions can scientific results be achieved with reasonable effort and in a relatively short time.

All of this applies to the mouse. With a life expectancy of two to three years, the entire life cycle can be examined much faster than, for example, in humans. Ten or more pups are born after a brief gestation of just three weeks. Mice also mate with close relatives. In this way, inbred lines can be created that are genetically very similar. This is important for scientists, as this is the only way to obtain exact and comparable results from their animal experiments.

In addition, for a long time scientists were only able to switch off individual genes in the mouse. Only in the last few years have new methods made this possible in other species as well. Hardly any other mammalian organism has been examined as thoroughly as the mouse today: its genome has been completely deciphered. The comparison of their genes with those of humans has shown that, despite their different appearance, mice are biologically very similar to humans: humans have 95 percent of the genes in the mouse's genetic makeup in a similar form. Many of the diseases in mice and humans have the same genetic cause.

Genetically Modified Mice

Researchers can switch genes in the genome of the mouse on or off at specific points in time during development and investigate the consequences. This allows conclusions to be drawn about the function of a gene. Mice with an altered variant of a gene often show similar tissue changes as human patients. This allows scientists to elucidate the origins of diseases in humans and their treatment. In 2015 were 55 percent of the mice kept at Max Planck Institutes are genetically modified.

In many cases, the genetically modified animals show no discernible changes. This is the case, for example, when a genetic defect is compensated for by other genes. Such genetic modifications have little or no effect on the animal and can only be detected with special methods or not at all.

Genetic changes rarely trigger symptoms of the disease: only three percent of the mice kept at Max Planck Institutes suffered from symptoms as a result of a deliberately induced mutation in 2015.

In principle, the scientists are obliged by legal requirements to keep the number of genetically modified test animals exposed to pollution as low as possible. You can minimize the number of such animals in various ways: for example, by breeding heterozygous animals - i.e. animals with only one disease-causing version of the gene - if the change only has a negative impact on animals that have two faulty gene copies.

If strains are to be expected in the event of a genetic change, the breeding of such animals is already classified as an animal experiment - regardless of which examinations are to be carried out on the animal later. Every scientist in Germany must therefore carry out an exposure assessment for a genetically modified strain. If the strain is expected or unexpected, he must have the breeding and keeping of this strain approved by the authorities.