Amule is the offspring of a horse and a donkey. a donkey sperm contains 31 chromosomes and a horse egg 32 chromosomes, so the zygote contains a total of 63 chromosomes. the zygote develops normally. the combined set of chromosomes is not a problem in mitosis, and the mule combines some of the best characteristics of horses and donkey. however, a mule is sterile; meiosis cannot occur normally in its testes and ovaries. explain why mitosis is normal in cells containing both horse and donkey chromosomes but the mixed set of chromosomes interferes with meiosis.