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Beginning The Developmental Program: Gametogenesis: Comparing Oogenesis and Spermatogenesis

Oogenesis and spermatogenesis are the processes by which eggs and sperm are produced through meiosis. During oogenesis, oogonia undergo mitosis before birth and enter meiosis I, arresting until puberty. Each month one oocyte completes meiosis I and II, forming one ovum and three polar bodies. Spermatogenesis produces four sperm through mitosis and equal cytokinesis after meiosis I and II. Spermatogenesis is regulated by FSH, LH, and testosterone, while oogenesis responds to FSH, LH, estrogen, and progesterone in a monthly cycle culminating in ovulation.

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143 views18 pages

Beginning The Developmental Program: Gametogenesis: Comparing Oogenesis and Spermatogenesis

Oogenesis and spermatogenesis are the processes by which eggs and sperm are produced through meiosis. During oogenesis, oogonia undergo mitosis before birth and enter meiosis I, arresting until puberty. Each month one oocyte completes meiosis I and II, forming one ovum and three polar bodies. Spermatogenesis produces four sperm through mitosis and equal cytokinesis after meiosis I and II. Spermatogenesis is regulated by FSH, LH, and testosterone, while oogenesis responds to FSH, LH, estrogen, and progesterone in a monthly cycle culminating in ovulation.

Uploaded by

Mielah Ruth
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© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Beginning the Developmental Program: Gametogenesis

Comparing Oogenesis and Spermatogenesis

Only genetic information from Germ Cells can be passed to the next generation. [Wolpert Fig. 1.6]

Gamtes are produced by Meiosis [Wolpert Fig. 12.17]

Comparing Eggs (Ova) & Sperm


Haploid
Products of Meiosis

Haploid
Products of Meiosis

Produced by female parent in ovary Non-motile gamete Large size


Cytoplasm contains RNA and Protein, nutrients

Produced by male parent in testis Motile gamete -agellum Small in comparison


Minimal amt. Cytoplasm

Structure of a Human Sperm [Wolpert Fig. 12.21]

[Gilbert Fig. 7.3]

Spermatogenesis produces 4 haploid Gametes

[Wolpert Fig. 12.18]

Spermatogenesis takes place in the seminiferous tubules in the testis. [Gilbert Fig. 19.19]

Meiosis is initiated continuously in a mitotically dividing stem cell population (= spermatogonia).

Oogenesis vs. Spermatogenesis (Mammals)


Germ Cells enter ovary
Diploid oogonia multiply by mitotic divisions during embryogenesis Enter prophase of Meiosis I before birth

Germ Cells enter testis


Arrest in G1 of cell cycle until after birth

Further growth and development of primary oocyte delayed until puberty

After birth, esp. after puberty, spermatogonia multiply by mitotic divisions

Oogenic Meiosis Oocytes in the human ovary completed the rst meiotic prophase before birth. Puberty induces completion of meiosis 1. Each month, ovulation triggers development through metaphase of meiosis 2. Fertilization triggers completion of meiosis 2.
[Gilbert Fig. 19.30]

Graaan follicle in a mammalian ovary [Balinsky Fig. 21]

Follicle cells synthesize Estrogen. Estrogen stimulates liver to produce vitellogenin

Oogenesis produces 1 Ovum & 3 Polar Bodies [Wolpert Fig. 12.8]

Oogenesis vs. Spermatogenesis


Growth and development Differentiation occurs after occurs before completion completion of Meiosis 1 & of Meiosis 1 2 One ovum & 3 polar bodies Four sperm are produced are produced from each from each primary primary oocyte spermatocyte
Unequal cytokineses Equal cytokineses

Regulation of Gametogenesis by hormones made in the Anterior Pituitary Gland FSH (= follicle stimulating hormone) LH (= Luteinizing hormone)
[Gilbert Fig. 19.30]

Oogenesis vs. Spermatogenesis


Regulated by
pituitary hormones: FSH and LH Ovarian hormones: estrogen and progesterone

Regulated by
pituitary hormones: FSH and LH Testicular hormones testosterone and androgen binding protein

Timing of Fertilization in relation to development of the oocyte [Wolpert Box 2A]

The Cycle Continues.


The egg and the sperm will both die if they do not meet. The elements that unite are single cells, each on the point of death; but by their union a rejuvenated individual is formed, which constitutes a link in the eternal process of life. Frank R. Lillie (1919)

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