The separation of duplicated chromosomes during mitosis was widely believed to be a random process. However, a group was recently able to distinguish the different DNA strands and regions on the chromosomes, and show the non-random segregation of chromosomes in colon epithelial cells. Image shows mouse chromosomes with these different labels.
Reference: Ester Falconer, Elizabeth A. Chavez, Alexander Henderson, Steven S. S. Poon, Steven McKinney, Lindsay Brown, David G. Huntsman & Peter M. Lansdorp. Adapted by permission from Macmillan Publishers Ltd: Nature 463, 93-97, copyright 2010. Paper can be found here.