Final answer:
A zygote with eight blastomeres (morula) typically appears around 72 hours after fertilization, occurring during the cleavage stage when cells divide without increasing the overall size.
Step-by-step explanation:
The approximate time after fertilization for a zygote with eight blastomeres (morula) is 72 hours. During this initial period, known as cleavage, the zygote divides mitotically to form two daughter cells, and this process continues every 12 to 24 hours. By day 4, this results in a solid ball of cells called the morula. The cleavage doesn't increase the overall size of the organism because the cells are confined within the zona pellucida, but the number of cells increases. It is only after reaching this stage that the morula continues down the fallopian tube toward the uterus, where it will eventually form a blastocyst.