Mitosis and Embryogenesis reviewer

EXERCISE 1. MITOSIS 

Use whitefish blastula – multi-celled early embryo (rapidly dividing)

1. Prophase – nucleolus disappears, centrosomes begin to move to

I.

II.

Interphase a. G1 phase – preparing for replication of DNA and organelles b. S phase - DNA is replicated c. G2 phase - checks DNA for any damage & ensures all the proteins needed for cell division are present Mitosis (Karyokinesis) – cell division in which one cell (the mother) divides to produce two new cells (the daughters) that are genetically identical to itself.

opposite poles 2. Metaphase – All the chromosomes align at the metaphase plate 3. Anaphase - sister chromatids separate from each other and are pulled towards opposite ends of the cell. - Each is now its own chromosome.

4. Telophase - the cell is nearly done dividing, and it starts to re-establish its normal structures as cytokinesis. - Two new nuclei form, one for each set of chromosomes. Nuclear membranes and nucleoli reappear.

III.

Cytokinesis - the division of the cytoplasm to form two new cells, overlaps with the final stages of mitosis. It may start in either anaphase or telophase - When cytokinesis finishes, we end up with two new cells, each with a complete set of chromosomes identical to those of the mother cell

EXERCISE NO. 2 GAMETOGENESIS I.

Spermatogenesis - is the process of sperm cell development. Rounded immature sperm cells undergo successive mitotic and meiotic divisions (spermatocytogenesis) and a metamorphic change (spermiogenesis) to produce spermatozoa. a. Frog Testes 1. Leydig cells or interstitial cells – somatic cells -

- Still diploid 5. Secondary spermatocytes – result of completion of meiosis I by primary spermatocytes. -

haploid few in number, because they rapidly enter meiosis II.

6. Spermatids – result of completion of meiosis II. -

very small and dense, like dots & very numerous haploid cells with half the chromosome number & half the DNA content

7. Spermatozoa – composed of sperm heads/ nuclei and sperm tails B. Mouse testes -

same parts as frog testes the stages will be arranged in layers from basement to inner lumen (messier in frog)

outside seminiferous tubules secretes testosterone 2. Sertoli cells – somatic cells -

within the seminiferous tubules NURSE CELLS for spermatozoa bind testosterone for use by the spermatocytes

II. OOGENESIS – or ovogenesis, is the production of an ovum (egg cell). It is developed from the primary oocyte by maturation. A. Frog Ovary 1. Theca externa – outer covering of the ovary 2. Theca interna

3. Spermatogonia – Stem cells of spermatogenesis with 2 fates: enter meiosis or continue to divide mitotically 4. Primary spermatocytes – cells that WILL enter meiosis. NEVER undergo mitosis.

3. Ooplasm – cytoplasm of the oocyte 4. Germinal vesicle – nucleus of the oocyte -

smaller dense body within nucleoli

5. Follicle cells – small flattened cells found along theca interna 6. Yolk platelets – oocyte varies in size from small to large, meaning there is continuous growth of these primary oocytes (diploid) -

as oocytes get larger, they accumulate yolk made in the liver and transported to the ovary

B. Cat Ovary 1. Tunica albuginea – outer covering of the ovary Cortex contains all the oocytes, medulla is innervated and vasculated 2. Premordial follicle – very small follicle located in bunches near the tunica albuginea -

contain primary oocytes-diploid, and arrested in the diplotene stage of prophase I.

3. Primary follicle, granulosa cells and zona pellucida – primary follicle is larger than the primordial follicle. -

contains single/multiple layers of granulosa cells, & no cavity inside has a zona pellicida covering

4. theca folliculi externa & interna – fibrous double outer coating outside the granulosa cells. -

inner most is theca folliculi interna (walls of the follicle) outer layer is the theca folliculi externa

5. Secondary follicle – distinguished by a very large, extensive antrum or cavity among the granulosa cells. 6. Tertiary follicle – a mature or Graafian follicle. -

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very large, extensive antrum & by a primary oocyte that has its own distinct layer of granulosa cells the cumulus oophorus has potential to ovulate, releasing an oocyte that will complete meiosis I to become a secondary oocyte. all the oocytes in the cat ovary are primary oocytes, and are all diploid

7. Atretic follicle – degenerating or dying follicles that fail to develop further or ovulate 8. Corpus luteum and albicans – form of thecal and granulosa cells after ovulation of a tertiary follicle. -

-Produces the hormone progesterone for possible implantation of a zygote if no implantation, the corpus luteum becomes a scar-like tissue, the corpus albicans.