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

Because the parents (male horse and female donkey) are different species.

Explanation:

A mule is an organism produced as a result of the fertilization of a donkey's egg by a horse's sperm. The parents of this hybrid animal (horse and a donkey) are two different species of animals with different number of chromosomes in their cells. The horse and donkey contains 64 and 62 chromosomes in their cells respectively.

These chromosomes numbers are reduced to 32 and 31 in the gametes of the horse and donkey respectively. However, when these gametes come together, they form a mule with 63 number of chromosomes (32+31). The two chromosomes of the different animal species form an hybrid that is different from both of the parents. Hence, the mule doesn't resemble the horse or donkey because the chromosomal (genetic) combination is different.

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.