BIPARENTAL INHERITANCE OF CHROMOSOME-21 POLYMORPHIC MARKERS INDICATESTHAT SOME ROBERTSONIAN TRANSLOCATIONS T(2121) OCCUR POSTZYGOTICALLY

Robertsonian translocations between acrocentric chromosomes are the mo st common structural chromosomal rearrangements in humans and many oth er organisms, and several mechanisms for their formation have been pro posed. We have analyzed highly informative DNA polymorphisms in a fami ly with a non-mosaic de novo Robertsonian translocation 21q;21q, to de termine the parental origin of the two 21q arms of the rearranged chro mosome. The genotypes indicated a biparental origin, i.e. one 21q was paternal and the other maternal. These results imply that in some case s the formation of the rob(21q;21q) occurs in the zygote or in the fir st few postzygotic mitotic divisions. (C) 1994 Wiley-Liss, Inc.