In the gametes of an individual hybrid the Anlagen for each individual parental character are found in all possible combinations but never in a single gamete the Anlagen for a pair of characters. Each combination occurs with approximately the same frequency.

'Mendel's Regel über das Verhalten der Nachkommenschaft der Rassenbastarde', Der Deutsche Botanische Gesellschaft, 1900, 18, 158–68. Trans. in Ernst Mayr, The Growth of Biological Thought: Diversity, Evolution and Inheritance (1982)