How does a morula form from a fertilized egg?

A morula forms through a series of rapid cellular divisions known as cleavage, which occur following the fertilization of an egg.12

During this process, the zygote undergoes mitosis to subdivide into smaller cells called blastomeres. Because these early divisions occur without significant growth, the total mass of the cluster remains approximately the same as the original zygote. In species with little yolk, such as humans, these cells divide completely and adhere to one another within a protective gelatinous capsule called the zona pellucida.321

By the fourth day after fertilization, this cluster typically consists of about 12 or more blastomeres and is referred to as a morula, a name derived from its resemblance to a mulberry. As the number of cells continues to increase, the morula eventually develops into a blastocyst, a hollow structure that prepares for implantation in the uterine lining.13