Healthy human cells have two (diploid) sets of chromosomes. However, it may also happens that cells have a tetraploid (quadruple) set. Usually, they do not divide further and die, but some cells can escape this fate. An international team of researchers, in which a research group from the Technische Universität Kaiserslautern (TUK) was involved, has now shown that many mutations occur in the cells immediately after they are formed. This is because they do not have enough proteins that are essential for the reproduction of the genetic material. The errors arising in this process lead to mutations and can promote tumor formation. The work has appeared in the journal Nature.