Why does oogenesis produce one egg

The larger cytoplasm rich cell is termed a secondary oocyte, while the smaller first polar body eventually dissolves.

The secondary oocyte briefly enters the second phase of meiosis, meiosis II. But this process again stops. Ovulation then releases this cell and those surrounding it from the ovary. And the complex migrates into a fallopian tube where fertilization occurs if sperm are present.

Meiosis resumes post fertilization and ends with a secondary oocyte dividing forming an undersized second polar body which similarly dissipates, and a larger ovum. The latter is the haploid mature egg in which distinct paternal and maternal nuclei are transiently visible.

Thus oogenesis only yields a single mature egg cell for every primary oocyte that successfully completes the process. In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis.

This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte containing most of the cytoplasm and minor polar body are produced as a result of meiosis I, and again following meiosis II.

Since only oocytes will go on to form embryos if fertilized, this unequal distribution of cell contents ensures that there are enough cytoplasm and nutrients to nourish the early stages of development. In mammals, oocytes are suspended in prophase I until sexual maturation, at which point meiosis I continues under hormonal influence until an egg precursor cell is released into a fallopian tube.

At ovulation, the precursor exits the ovary and, only if fertilization occurs, is stimulated to complete meiosis II and form a complete egg. Defects during oogenesis can result in severe consequences. In particular, problems with chromosome segregation during either meiosis I or meiosis II may lead to an embryo being aneuploid, meaning that it contains an abnormal number of chromosomes.

As a result, women who are 35 years and older are typically offered prenatal testing, such as blood tests, nuchal translucency screening by ultrasound, chorionic villus sampling, or amniocentesis, which can determine whether a fetus carries any chromosomal abnormalities. Interestingly, oocytes collected from women with endometriosis undergoing in vitro fertilization may show defects in the meiotic spindle apparatus or decreases in fertilization rates.

Research on this disease is ongoing, but some scientists have hypothesized that such poor oocyte quality may be the result of increased immune-associated proteins or altered hormone levels in these patients. Finally, other work has been performed to determine the effect of environmental factors on oogenesis, and their relation to aneuploidy.

Chewing tobacco, hormone use especially in older women and even exposure to bisphenol-A, a component of many plastics, have all been suggested to affect oogenesis adversely and the process of meiosis therein. Loane, Maria, Joan K.

To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired. Provide feedback to your librarian. If you have any questions, please do not hesitate to reach out to our customer success team. Login processing Chapter Reproduction and Development. Chapter 1: Scientific Inquiry. Chapter 2: Chemistry of Life. Chapter 3: Macromolecules. Chapter 4: Cell Structure and Function.

Chapter 5: Membranes and Cellular Transport. Chapter 6: Cell Signaling. Correct answer: Ovum. Explanation : The female gamete is called the ovum ova, plural. Example Question 7 : Understanding Oogenesis. Possible Answers: diploid. Correct answer: haploid. Explanation : After completing meiosis II, ova are haploid cells containing one chromosome. Example Question 8 : Understanding Oogenesis.

Possible Answers: oogenesis. Correct answer: ovulation. Explanation : The release of the secondary oocyte from the ovaries is ovulation. Example Question 9 : Understanding Oogenesis.

Possible Answers: Anaphase I. Correct answer: Prophase I. Explanation : Primary oocytes enter meiosis I and replicate their genomes, but they do not make their first meiotic division. Example Question 10 : Understanding Oogenesis. Possible Answers: an embryo. Correct answer: a secondary oocyte.

Explanation : A primary oocyte becomes a secondary oocyte when the follicle grows and matures and the primary oocyte completes its first meiotic division. Copyright Notice. View Tutors. Erin Certified Tutor. Kimberly Certified Tutor. Michael Certified Tutor. Report an issue with this question If you've found an issue with this question, please let us know.

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Your Full Name. Phone Number. Zip Code. Track your scores, create tests, and take your learning to the next level! Top Subjects. Our Company. Varsity Tutors. Privacy Policy. Terms of Use. Sign In. Email address: Your name: Feedback:. Spermatogenesis occurs in the wall of the seminiferous tubules, with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube.

Immediately under the capsule of the tubule are diploid, undifferentiated cells. These stem cells, called spermatogonia singular: spermatagonium , go through mitosis with one offspring going on to differentiate into a sperm cell, while the other gives rise to the next generation of sperm. Meiosis begins with a cell called a primary spermatocyte. At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte. This haploid cell must go through another meiotic cell division.

The cell produced at the end of meiosis is called a spermatid. Four sperm result from each primary spermatocyte that goes through meiosis. Stem cells are deposited during gestation and are present at birth through the beginning of adolescence, but in an inactive state. During adolescence, gonadotropic hormones from the anterior pituitary cause the activation of these cells and the production of viable sperm.

This continues into old age. Learning Objectives Distinguish between spermatogenesis and oogenesis. Key Points Gametogenesis, the production of sperm spermatogenesis and eggs oogenesis , takes place through the process of meiosis.

In oogenesis, diploid oogonium go through mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but then arrest; it will finish this division as it develops in the follicle, giving rise to a haploid secondary oocyte and a smaller polar body.