Sterile hybrid with genome AB undergoes doubling of chromosome set to form fertile tetraploid with genome AABB. But since A and B is not homologous, synapsis cannot occur at prophase I, so there is no meiosis. So how does the chromosomes double? If through non-disjunction in mitosis, where did it occur? Did it occur in one cell only or all of the cells in the organism? Did non-disjunction occurs at gonad to produce AABB cell, then it undergo meiosis to form AB gametes, and then self fertilise with AB gamete to form AABB offspring?