Fig. 1. Chocolate cake with strawberry icing (A,B) and epithelial cell versus neuroblast division (C,D). (A) Symmetric division: a vertical slice divides the cake into two pieces of equal size and content, both containing the same amount of chocolate cake and strawberry icing. (B) Asymmetric division: a horizontal slice yields two pieces of unequal size and content, a large piece of chocolate cake and a small piece of cake with all of the icing. (C) Epithelial cells (red) divide symmetrically, giving rise to two equal cells. Cell fate determinants (green) localised at the basolateral cortex are partitioned equally to both daughter cells. (D) Neuroblast (blue) divisions are intrinsically asymmetric: the two daughter cells differ in cell size, mitotic potential and cell fate. Asymmetrically localised cell fate determinants, such as proteins or mRNAs (green), are segregated asymmetrically into the basal GMC. Apical is up and basal is down.