Schematic representation of the events leading to the mosaicism in cases 1 and 6. A) In case 1, there was likely a recombination between the two paternal homologous chromosomes 13, followed by a duplication of part of the recombined chromosome. A subsequent non-disjunction resulted in a trisomic zygote, that lead to a normal and an abnormal cell line through two trisomy rescue events. B) The mosaicism in case 6 presumably originated from a translocation between chromosome 1 and chromosome 20 during meiosis I, with segregation of a normal and a derivative chromosome 20 to the zygote. This results in a zygote which is trisomic for chromosome 20p and 1q and could lead to the mosaicism seen in this case by trisomy rescue of the derivative chromosome (normal cells) and trisomy rescue of a normal chromosome 20 (abnormal cells).