A cross between a male horse and female donkey results in reproduction of a mule, which does not resemble either oft he parents. What is the reason for this

When a male horse is crossed with the female donkey, a mule is produced. They have identical chromosome complement which make them compatible to mate. but they differ genetically due to the phenotype characteristics which is due the presence of allele on the chromosomes and thus ave a different and unpredictable offspring. Mule is produced due to the sexual reproduction between male horse and female donkey, Thus it has different genetic combination from both of them.