Gametogenesis and Oogenesis Overview

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Questions and Answers

What is the main purpose of primordial germ cells during early development?

To differentiate into gametes in the gonads (correct)

To migrate to the yolk sac for nourishment

To produce hormones for gonadal development

To initiate immune response in the embryo

At what point do primordial germ cells begin to migrate toward the developing gonads?

At the end of the 4th week (correct)

At the beginning of the 5th week

After the completion of mitosis

During the 2nd week of development

What type of division occurs to increase the number of germ cells during their migration?

Binary fission

Maturation division

Meiotic division

Mitotic division (correct)

How long do primary spermatocytes remain in prophase of the 1st meiotic division?

22 days Signup and view all the answers

What is the chromosome number of secondary spermatocytes?

23 chromosomes (1N) Signup and view all the answers

What does the term 'n' refer to in the context of gametogenesis?

The haploid number of chromosomes Signup and view all the answers

What process follows the formation of secondary spermatocytes?

Meiosis II Signup and view all the answers

What do primordial germ cells differentiate into upon reaching the ovaries?

Oogonia Signup and view all the answers

What is the chromosome number of a primary gametocyte before meiosis?

46 chromosomes (2n) Signup and view all the answers

What is a key feature of the cluster of cells formed from type A spermatogonia?

They maintain contact throughout differentiation. Signup and view all the answers

Which phase of meiosis does the transition from primary gametocyte to secondary gametocyte occur?

Meiosis I Telophase Signup and view all the answers

Which of the following changes does NOT occur during spermiogenesis?

Replication of genetic material Signup and view all the answers

What process occurs when a Graafian follicle ruptures?

Ovulation of the ovum Signup and view all the answers

What happens to the number of germ cells when they arrive in the gonad?

They continue to proliferate through mitosis Signup and view all the answers

What is the role of oocyte maturation inhibitor (OMI)?

To prevent maturation of primary oocytes Signup and view all the answers

What happens to the cytoplasm during the transformation of spermatids to sperm cells?

It is shed excessively. Signup and view all the answers

At which stage do primary oocytes remain until puberty?

Prophase I Signup and view all the answers

What is the estimated number of primary oocytes present at birth?

700,000 - 2 million Signup and view all the answers

What is the role of Sertoli cells in spermatogenesis?

To provide support and protection Signup and view all the answers

What is the primary function of the acrosome formed during spermiogenesis?

To aid in penetration of the ovum Signup and view all the answers

By the 7th month of pregnancy, what happens to the majority of oogonia?

They degenerate except for a few Signup and view all the answers

How many primary oocytes are generally present by the onset of puberty?

400,000 Signup and view all the answers

What happens to a primordial follicle during the ovarian cycle?

It begins to mature Signup and view all the answers

What occurs to Type A spermatogonia during normal progression?

They divide and give rise to Type B spermatogonia. Signup and view all the answers

What is the composition of the secondary oocyte and the first polar body in terms of chromosomes and DNA?

Both have 23 chromosomes and double amount of DNA. Signup and view all the answers

At what stage is the secondary oocyte arrested before ovulation?

Metaphase of meiosis II. Signup and view all the answers

What completes the second meiotic division of the secondary oocyte?

It completes only if the oocyte is fertilized. Signup and view all the answers

What is the fate of the unequal daughter cells formed after the first meiotic division of a primary oocyte?

One becomes a secondary oocyte, the other a polar body Signup and view all the answers

What happens to an oocyte if it is not fertilized within 24 hours after ovulation?

It degenerates. Signup and view all the answers

What initiates the transformation of spermatogonia into spermatozoa?

The presence of hormonal signals. Signup and view all the answers

What type of germ cells can be recognized at the time of birth in male sex cords?

Spermatogonia of Type A. Signup and view all the answers

Which of the following best describes spermatogonia?

They originate from primordial germ cells. Signup and view all the answers

Study Notes

Gametogenesis

Gametes are derived from primordial germ cells (PGCs) formed in the epiblast during the second week of development
PGCs migrate to the wall of the yolk sac
PGCs migrate from the yolk sac to the developing gonads during the fourth week
During migration, PGCs undergo mitosis to increase their numbers

Oogenesis Overview

Oogenesis begins with primordial germ cells differentiating into oogonia
Oogonia undergo mitotic divisions surrounded by flat epithelial cells (follicular cells)
By the end of the third month of pregnancy, each ovary contains 7 million oogonia
Some oogonia enter prophase I of meiosis I and become primary oocytes
By the end of the fifth month, primary oocytes arrest their cell division in prophase of meiosis I and form primary oocytes
By the seventh month, most oogonia degenerate, except for some near the ovarian surface

Oogenesis - Postnatal Maturation

Primary oocytes remain in prophase I until puberty due to an oocyte maturation inhibitor (OMI) secreted by the follicular cells
At birth, there are approximately 700,000 - 2 million primary oocytes
During childhood, the number decreases to around 400,000
Only a few hundred oocytes (less than 500) will ovulate during a woman’s lifetime
At puberty, 15-20 primordial follicles mature each ovarian cycle
One follicle continues to develop into a growing primary, secondary, and Graafian follicle
The rupture of the Graafian follicle releases the ovum, which is captured by the fallopian tube fimbria
The primary oocyte completes meiosis I and forms two daughter cells: a secondary oocyte and a first polar body
The secondary oocyte receives most of the cytoplasm while the first polar body receives very little
Both the secondary oocyte and first polar body have 23 chromosomes (1n) and double the amount of DNA (2N)
The secondary oocyte enters meiosis II but arrests in metaphase II about 3 hours before ovulation
Meiosis II is completed only if fertilization occurs; otherwise, the oocyte degenerates within 24 hours
The first polar body also enters meiosis II without DNA replication

Spermatogenesis Overview

Begins with spermatogonia in the sex cords of the testis, which differentiate into spermatogonia Type A and Type B
Spermatogonia Type A divide and give rise to Type B spermatogonia
Type B spermatogonia undergo mitosis to produce primary spermatocytes
Primary spermatocytes enter a prolonged prophase of meiosis I (22 days)

Spermatogenesis - Meiosis I & II

Meiosis I is completed rapidly, resulting in the formation of secondary spermatocytes with 23 chromosomes (1n) and double the amount of DNA (2N)
Secondary spermatocytes immediately enter meiosis II to form spermatids

Spermatogenesis - Spermiogenesis

Cytokinesis is not completed during the progression from type A spermatogonia to spermatids, forming a cluster of cells connected during differentiation
Spermatids remain in contact with Sertoli cells for support and protection
Spermiogenesis transforms rounded spermatids into elongated, motile sperm cells

Spermiogenesis Changes

Formation of an acrosome, which helps penetrate the ovum
Condensation of the nucleus
Development of a neck, middle piece, and tail
Shedding of most of the cytoplasm

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Description

Learn about the intricate processes of gametogenesis and oogenesis, including the migration of primordial germ cells and the stages of oocyte development. This quiz covers the timeline from the formation of primordial germ cells to the maturation of oocytes postnatally. Test your knowledge on these critical concepts in reproductive biology.