Describe the process of oogenesis. Are the polar bodies functional or non-functional entities? What is the advantage of the unequal cytokinesis that occurs during oocyte production? In addition to genetic material, what does the ovum supply to the embryo once fertilization takes place?
Oogenesis occurs within the follicles of the ovaries. The meiosis of oocytes always results in haploid cells of unequal size. When a primary oocyte undergoes meiosis, a large haploid secondary oocyte and a very small first polar body result. A second meiotic division produces a large ootid and a very small second polar body. The first polar body may or may not divide during the second meiotic division into two additional second polar bodies. All the polar bodies are non-functional. After meiosis, the ootid quickly differentiates into the mature egg cell or ovum. The unequal cytokinesis that occurs has the advantage of providing the ovum with a much greater amount of cytoplasm and stored food than if an equal division were to occur. Thus, the non-motile ovum supplies a developing embryo with most of its cytoplasm and food while the much smaller but highly-motile sperm contributes mainly genetic material to the embryo.
