Role of acrocentric cen-pter satellite DNA in Robertsonian translocation and chromosomal non-disjunction.

The centromeres and short arms of the human acrocentric chromosomes have in common several families of tandemly repeated DNA. Recent analyses have revealed that, within some of these families, clearly distinct subfamilies have evolved that are unique to one or a subset of the different acrocentric chromosomes. The existence and maintenance of subfamilies common to different chromosomes entail a process of regular exchange between the non-homologous chromosomes. This process is suggested for the evolution of an alpha satellite subfamily recently found on chromosomes 13, 14 and 21. The presence of this alpha subfamily may allow pairing between these chromosomes leading to the observed non-random participation of these chromosomes in t(13q14q) and t(14q21q) Robertsonian translocations. The available data also indicate a very similar molecular organisation of the cen-pter region for chromosomes 13 and 21. This latter feature may further allow the two chromosomes to undergo a relatively extensive degree of meiotic pairing (in a manner analogous to that seen in the pseudoautosomal regions of the X and Y chromosomes), thus predisposing these two chromosomes to errors in meiotic segregation and non-disjunction.