Simplified representation of the nature of the most relevant (epi)genetic alterations in (neuro-)oncology. Normal DNA is displayed at the top, with part of another chromosome to the right. At the bottom, altered DNA is represented. The depicted alterations are examples. The mutation shows a change from a cytosine (C)-guanine (G) base pair to a thymine (T)-adenosine (A) base pair. A copy number change may involve a loss/deletion or a gain/amplification, of which the latter is shown here (from 1 to 4 copies of a single gene). The depicted deletion now involves loss of part of 1 single gene, but a deletion may also concern loss of a partial or whole chromosome arm. A gene fusion, depicted as a fusion between genes that were already on the same chromosome arm, may also concern fusion between genes originating on different chromosome arms. The translocation shows the addition of part of 1 arm of a chromosome to the arm of another chromosome.