What happens in a mules chromosomes when it's sterile?

Mules are sterile due to their unique chromosome composition, resulting from the crossbreeding of a horse (64 chromosomes) and a donkey (62 chromosomes), resulting in 63 chromosomes. This odd number prevents proper pairing during meiOSis, the process of forming gametes. As a result, mules cannot produce functional sperm or eggs, leading to sterility.