Chromosomal aberrations

Alteration of the chromosome structure through loss, exchange or duplication of segments, whereby both chromatids of a chromosome are affected. With the exception of deficiencies (loss of chromosome ends), chromosome aberrations are caused by illegitimate crossing over, i.e. crossing over at non-homologous sites (e.g. after exposure to radiation, by chemical mutagens). Crossing over leads to deletion (loss of a middle piece), inversion (exchange of the two ends) or formation of ring chromosomes.

Large changes in the chromosomes are referred to as structural chromosomal aberrations or chromosomal mutations.

Four different types of chromosome mutations are possible:

• Duplication: Larger sections of the chromosome are copied more than once, making the chromosome considerably longer. Duplication of part of chromosome 15 leads to a form of autism.
• Inversion: Part of the chromosome is cut out and reinserted in the wrong direction. This leads to a reversed order of the genes. If the inversion affects the centromere, it is called pericentric; if it is outside the centromere, it is called paracentric.
• Deletion: Large sections of the chromosome are lost
• Translocation: Parts between non-homologous chromosomes are swapped.