What does the zygote form once it starts mitosis?

Once a zygote begins dividing by mitosis, it develops into an embryo. The zygote is the single cell formed when a sperm fertilizes an egg, and its first mitotic divisions produce more cells without increasing the embryo’s overall size very much.

These early divisions are called cleavage. They create a compact cluster of cells known as a morula, followed by a blastula; in humans, this stage is called a blastocyst. The blastocyst later implants in the uterine lining, where cells begin organizing into the tissues and structures of the developing embryo.

The zygote itself is therefore the earliest one-cell stage of development, while “embryo” describes the multicellular organism during the early developmental period. In human development, the embryonic period generally extends through the eighth week after fertilization; afterward, the developing individual is usually called a fetus. A common mix-up is treating mitosis as the process that creates genetically different cells. Early mitotic divisions copy the zygote’s genome, while later cell specialization gives those cells different roles.