Optometry Admission Test (OAT) Practice

Mitotic division occurs during the cleavage stage after fertilization. Cleavage is characterized by a series of rapid cell divisions (mitosis) that transform the single fertilized egg (zygote) into a multicellular structure called the morula. During this stage, the cells begin dividing without significant growth, leading to a rapid increase in the number of cells while the overall size of the embryo remains relatively constant. Implantation occurs later when the embryo attaches to the uterine wall, and it does not involve further divisions of cells but rather the embedding of the embryo. Gastrulation is the next stage after cleavage, where cell migration leads to the formation of three distinct layers of cells (ectoderm, mesoderm, and endoderm). Neurulation follows gastrulation and involves the development of the nervous system but does not involve mitotic divisions like those seen in cleavage. Therefore, the correct answer highlights the critical role of cleavage in the early stages of embryonic development following fertilization.