Figure 1.

 Chromosome methylation patterns of mouse embryos at the one-cell stage. Methylated sites were revealed by indirect immunofluorescence labeling with 5-MeC monoclonal antibody. (A,B) Metaphases from normal mouse embryos obtained without (A) and with (B) colchicine treatment. (A) Two distinct sets of 20 chromosomes each are observed (in mouse 2n = 40). One chromosome set displays an intense R-like banding pattern (right, medium thin arrow). The other set is faintly labeled (left, long thin arrow). Centromeric heterochromatin (small thick arrows) is labeled intensely in only a few chromosomes of the first set, whereas it is labeled in most chromosomes of the second set. (C) Parthenogenetic embryos: all chromosomes display an R-like banding pattern confirming that more labeled chromosomes in normal embryos are of maternal origin. (D) Chromosomes from an embryo carrying Robertsonian translocations of paternal origin: Normal maternal chromosomes (medium thin arrow) are labeled more intensely than paternal translocated chromosomes (long thin arrow).