Question

Which of the following characteristics does not belong to cleavage?

• A. Decrease in size of blastomeres
• B. Rapid mitotic cell division
• C. Interphase of very short duration
• D. Differentiation of blastomeres

Answer 1

The correct option is D Differentiation of blastomeres

After fertilization, the zygote will begin to undergo development. This single cell will eventually give rise to every cell that will make up the person it will develop into. During the first four days after fertilization, the stage known as cleavage, the principle developmental mechanism that is being employed is (rapid) cell division, or (rapid) mitosis (with a very reduced or short interphase). The process of cleavage involves a series of cell divisions that are not accompanied by any growth. Essentially what is occurring is that the relatively large zygote is subdivided into a number of smaller cells, whose combined size is approximately the same as the zygote. During this time, approximately five cell divisions occur, resulting in 32 cells. These 32 cells are essentially identical to one another and are all clustered together in a single mass. This mass of cells is called as the morula, which literally means little mulberry and is based on the clustered appearance of the cells at this stage. This process is fueled by nutrients present in the original oocyte. These nutrients are not sufficient, however, as a supply for the entire developmental process. To obtain nutrients to support subsequent development, the pre-embryo will ultimately have to attach to the mother.

Thus, the correct option is (D).