Slides 11-20 show meiosis in the ovary of a female Ascaris worm. Oogenesis in the Ascaris is unusual in that meiosis does not begin until the egg is penetrated by the sperm. Penetration initiates the process of oogenesis. These slides are difficult and you are not expected to be able to identify individual slides, but to explain the process.

Slide11.jpg

Sperm entrance. Shown here is the large primary oocyte that will mature into the female gamete, or ovum, following meiosis. The characteristically bullet-shaped sperm cell has already penetrated the oocyte. The penetration of the sperm induces two changes in the egg: First, vesicles in the outer region of the egg cytoplasm release their contents to form a fertilization membrane (not visible here) surrounding the egg. This acts as a barrier against the entry of additional sperm. Second, penetration of the sperm into the oocyte induces maturation of the egg (i.e., the egg will undergo meiosis). The sperm cell is the mature male gamete, and therefore haploid at this stage, but the oocyte is immature and still diploid. Its nucleus can be seen as a diffuse dark area in the center of the cell. Notice the large vacuoles in the oocyte.



Alternate Slides:

BIOG 1106 - Unit 1 Slides