Answer:
reduced hybrid fertility
Step-by-step explanation
The formation of mules from the cross between female horses (mares) and male donkeys (jacks) is an example of reduced fertility because the mules are sterile and they cannot give birth to babies.
Reason:
Because mule cannot produce sperms. This has to do with his genetics. A mule has 63 chromosomes in total. He gets 32 chromosomes from his mom (that is a horse) and 31 chromosomes from his Dad (that is a donkey). As we know, it is very important for reproduction that chromosomes hould be present in two sets with equal numbers.
To reproduce he needs equal number of chromosomes because we know during meiosis chromosomes segregate and half number goes in daughter cells. But in case of mules he has an extra chromosome due to which he cannot undergo correct meiosis and produce sperms. That is ahy he stays sterile throughout his life. This is called reduced hybrid fertility
Hope it helps!