Gametogenesis Overview
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Questions and Answers

What is the function of hyaluronidase in sperm fertilization?

  • To condense chromatin in the sperm
  • To produce ATP for sperm motility
  • To enable sperm to penetrate the oocyte (correct)
  • To activate the egg

What characterizes the nuclear morphogenesis of sperm?

  • Increased size and loose chromatin
  • Decreased density and round shape
  • Condensation of chromatin and change to an oval shape (correct)
  • Formation of multiple nuclei

How do mitochondria contribute to the sperm structure?

  • They form a spiral structure around the tail for energy production (correct)
  • They store genetic information
  • They help in the elongation of microtubules
  • They organize the acrosome

What indicates a low sperm count condition?

<p>Oligozoospermia (A)</p> Signup and view all the answers

What role does ZP3 play in fertilization?

<p>It mediates sperm-specific egg binding (B)</p> Signup and view all the answers

Which component is essential for the contact and fusion of sperm and egg membranes?

<p>ADAM membrane protein (B)</p> Signup and view all the answers

What is the main function of the acrosomal reaction during fertilization?

<p>To release enzymes necessary for penetrating the egg coat (D)</p> Signup and view all the answers

What signifies a Sertoli cell only syndrome?

<p>Presence of only Sertoli cells in seminiferous tubules (D)</p> Signup and view all the answers

What role does retinoic acid play in meiosis?

<p>It induces meiosis. (A)</p> Signup and view all the answers

Which factors prevent the onset of meiosis in mouse Sertoli cells?

<p>FGF9 and CYP26B1 (D)</p> Signup and view all the answers

During which spermatogenesis period does mitosis of spermatogonia occur?

<p>Proliferation period (D)</p> Signup and view all the answers

What is the primary function of Sertoli cells?

<p>Support and nourish developing sperm cells (C)</p> Signup and view all the answers

Which stage of spermatogenesis directly leads to the formation of spermatozoa?

<p>Spermiogenesis (C)</p> Signup and view all the answers

What hormone does Sertoli cells produce to inhibit meiosis during embryonic life?

<p>PGD2 (C)</p> Signup and view all the answers

How long does the maturation period of spermatogenesis typically last?

<p>22 - 24 days (A)</p> Signup and view all the answers

What is a distinguishing feature of the growth period in spermatogenesis?

<p>Weak growth compared to oogenesis (A)</p> Signup and view all the answers

What type of junction is formed between Sertoli cells and developing sperm cells?

<p>Tight junctions (C)</p> Signup and view all the answers

What cellular event occurs during the maturation period of spermatogenesis?

<p>Primary spermatocytes undergo meiosis (C)</p> Signup and view all the answers

What is the primary role of the SRY gene in male sex determination?

<p>To regulate the expression of SOX9 (C)</p> Signup and view all the answers

In which phase does oogenesis first halt during meiosis?

<p>Prophase I of meiosis I (A)</p> Signup and view all the answers

How does the epigenetic regulation during gametogenesis occur in PGCs?

<p>With widespread chromatin modifications and demethylation (A)</p> Signup and view all the answers

When does spermatogenesis begin in males?

<p>At puberty and continues throughout life (D)</p> Signup and view all the answers

What does SOX9 regulate during male sex determination?

<p>The differentiation of Sertoli cells (A)</p> Signup and view all the answers

Which of the following accurately describes the maturation period of oogenesis?

<p>Finishes only after the occurrence of fertilization (A)</p> Signup and view all the answers

What significant process occurs during the migration of PGCs?

<p>Change in epigenetic marks from demethylation (A)</p> Signup and view all the answers

What is an important marker of primordial germ cells (PGCs)?

<p>Alkaline phosphatase (D)</p> Signup and view all the answers

Which epigenetic modification is crucial for proper chromosome segregation in developing gametes?

<p>Histone methylation (A)</p> Signup and view all the answers

What initiates the gonadal differentiation process during embryonic development?

<p>Expression of interferon-induced proteins (D)</p> Signup and view all the answers

What is the primary role of the Akap82 protein?

<p>Tail formation (D)</p> Signup and view all the answers

During cytokinesis, what is unique about male sex cell precursors?

<p>They remain cytoplasmically attached (B)</p> Signup and view all the answers

What major event occurs during spermiogenesis regarding cytoplasm?

<p>Shedding of most of the cytoplasm (C)</p> Signup and view all the answers

From where is the acrosome formed during spermiogenesis?

<p>Golgi complex (A)</p> Signup and view all the answers

Which of the following is true about the Akap82 gene?

<p>Responsible for tail structure development (B)</p> Signup and view all the answers

What key signal indicates the completion of meiosis in the oocyte?

<p>Increase in Ca2+ levels in the egg cytoplasm (D)</p> Signup and view all the answers

What process is prevented by the enzymes released from cortical granules during fertilization?

<p>Polyspermy (C)</p> Signup and view all the answers

Which of the following accurately describes a consequence of fertilization?

<p>Restoration of the diploid chromosome number (D)</p> Signup and view all the answers

What occurs during the cleavage stage following fertilization?

<p>Series of mitotic divisions and cytokinesis (A)</p> Signup and view all the answers

What is one of the key functions of Sertoli cells during spermatogenesis?

<p>To synchronize the events of spermatogenesis (D)</p> Signup and view all the answers

Which structure is primarily involved in the nourishment and protection of developing sperm cells?

<p>Sertoli cells (D)</p> Signup and view all the answers

In which period of spermatogenesis do spermatogonia undergo mitotic divisions?

<p>Proliferation period (B)</p> Signup and view all the answers

What is the primary outcome of Meiosis I during spermatogenesis?

<p>Generation of secondary spermatocytes (B)</p> Signup and view all the answers

Which protein is specifically noted to prevent meiosis in mouse Sertoli cells?

<p>CYP26B1 (A)</p> Signup and view all the answers

What characterizes the structure of Sertoli cells?

<p>Well-developed smooth ER (C)</p> Signup and view all the answers

During which stage does the transformation of spermatids into mature spermatozoa occur?

<p>Spermiogenesis (C)</p> Signup and view all the answers

What is the primary function of the acrosomal reaction in sperm fertilization?

<p>To allow sperm to penetrate the zona pellucida (C)</p> Signup and view all the answers

What is the main reason for retinoic acid's role in meiosis initiation?

<p>It acts as a meiosis inducer (B)</p> Signup and view all the answers

Which enzyme is NOT involved in helping sperm penetrate the oocyte?

<p>Lactase (D)</p> Signup and view all the answers

What primary change occurs during nuclear morphogenesis of sperm?

<p>Condensation of chromatin (B)</p> Signup and view all the answers

What occurs during the growth period of spermatogenesis?

<p>Formation of secondary spermatocytes (D)</p> Signup and view all the answers

What structural feature is crucial for the motility of sperm?

<p>Flagellum (A)</p> Signup and view all the answers

Which characteristic is associated with the maturation period of spermatogenesis?

<p>Formation of cytoplasmic bridges (D)</p> Signup and view all the answers

Which condition is characterized by the absence of sperm in the ejaculate?

<p>Azoospermia (B)</p> Signup and view all the answers

Which receptor molecule on the egg membrane is directly involved in sperm binding?

<p>ZP2 (A)</p> Signup and view all the answers

What occurs to the oocyte during the maturation period of oogenesis?

<p>It undergoes meiosis II and completes cytokinesis. (A)</p> Signup and view all the answers

Which structure is formed during the development of a secondary follicle?

<p>Antrum (A)</p> Signup and view all the answers

Which of the following best describes the role of ZP1 in fertilization?

<p>Helps in structural integrity of the zona pellucida (C)</p> Signup and view all the answers

What is the role of MPF in oogenesis?

<p>To promote chromosome condensation and nuclear envelope breakdown. (C)</p> Signup and view all the answers

During which process do mitochondria in sperm rearrange to support motility?

<p>Fusion and spiral formation (B)</p> Signup and view all the answers

What characterizes the mature follicle, also known as the Graafian follicle?

<p>Significant enlargement of the antrum. (C)</p> Signup and view all the answers

How does cytokinesis occur during oogenesis?

<p>It is unequal, producing one large oocyte and one small polar body. (D)</p> Signup and view all the answers

Which hormone is primarily involved in the regulation of meiosis during oogenesis?

<p>MPF (Maturation Promoting Factor) (C)</p> Signup and view all the answers

What happens to one of the cells produced during cytokinesis in oogenesis?

<p>It degenerates and contributes to the polar body. (B)</p> Signup and view all the answers

Which of the following features uniquely characterize oocyte arrest in metaphase II?

<p>A control mechanism involving MPF and APC. (B)</p> Signup and view all the answers

What is the primary purpose of the SRY gene during sex determination?

<p>Upregulating SOX9 expression during a critical window (A)</p> Signup and view all the answers

During which phase does oogenesis first arrest in meiosis?

<p>Prophase I (A)</p> Signup and view all the answers

What significant event occurs during the migration of primordial germ cells (PGCs)?

<p>Expressions of IFITM1 and IFITM3 proteins (D)</p> Signup and view all the answers

What is the final outcome of meiosis II in oogenesis?

<p>Completion of oocyte formation (B)</p> Signup and view all the answers

Which process marks the remethylation of the germ cell genome during fetal life?

<p>Epigenetic resetting (D)</p> Signup and view all the answers

At which stage of embryonic development do primordial germ cells (PGCs) rise in the yolk sac?

<p>4 weeks (D)</p> Signup and view all the answers

What is the role of the enzyme PRDM9 during gametogenesis?

<p>Transferring a methyl group to H3K4 (A)</p> Signup and view all the answers

What distinguishes the growth period of oogenesis?

<p>Formation of secondary oocytes (D)</p> Signup and view all the answers

Which of the following best describes the timing of spermatogenesis in males?

<p>Starts at puberty and continues throughout life (B)</p> Signup and view all the answers

Which event marks the wide changes in epigenetic marks of PGCs during development?

<p>Chromatin modification during migration (D)</p> Signup and view all the answers

Flashcards

Sertoli cells

Tall columnar epithelial cells in the testes; support and nourish developing sperm cells.

Spermatogenesis

The process of sperm production in males.

Spermatogonia

Undifferentiated germ cells that multiply by mitosis.

Meiosis

A type of cell division that reduces the chromosome number by half, producing haploid cells.

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Spermatocytes

Cells formed from spermatogonia, undergoing meiosis.

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Spermatids

Cells resulting from meiosis, that mature into spermatozoa (sperm).

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Sertoli cells' function

Produce proteins for sperm development and create the blood-testis barrier.

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Hemato-testicular barrier

A barrier created by tight junctions between Sertoli cells, isolating developing sperm from the immune system.

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Spermatogenesis stages

A multistep process with proliferation, growth, maturation, and spermiogenesis.

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Proliferation period

Spermatogonia multiply by mitosis, beginning in embryonic life.

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PGCs

Primordial germ cells, precursors to gametes, that originate in the yolk sac during early pregnancy.

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IFITM1 and IFITM3

These proteins help guide PGCs to the genital ridge during their early migration.

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What is the key role of SRY?

SRY, a gene on the Y chromosome, mainly activates the SOX9 gene, triggering the development of male characteristics.

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SOX9

A crucial gene, regulated by SRY, that guides the differentiation of Sertoli cells, vital for sperm production.

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Epigenetic marks in gametogenesis

These are chemical modifications to DNA that don't change the sequence but impact gene expression. They are crucial during gamete development for proper inheritance.

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Genome-wide demethylation in PGCs

PGCs undergo a widespread removal of methyl groups from their DNA, essentially resetting their epigenetic marks.

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X chromosome re-activation in PGCs

In female PGCs, the deactivated X chromosome is reactivated, restoring full functionality.

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Histone modifications

These changes to histone proteins, which package DNA, influence gene accessibility and regulate gene expression.

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Timing of gametogenesis in males

Sperm production begins at puberty and continues throughout a male's lifetime.

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Timing of gametogenesis in females

Egg production (oogenesis) starts during embryonic development and continues until ovulation, with each oocyte having a limited lifespan.

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Acrosin, hylauronidase, neuraminidase

These are enzymes found in the acrosome of a sperm cell, crucial for penetrating the protective layers of the egg (oocyte) during fertilization.

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Nuclear morphogenesis

The transformation of the sperm nucleus, undergoing significant changes in shape, density, and structure, preparing it for fertilization.

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Tail formation

The intricate process where the microtubules in the sperm elongate, forming a tail structure for movement.

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Mitochondria fusion

Sperm mitochondria fuse together, forming a spiral around the tail, providing the energy needed for the sperm's movement.

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Sperm cell structure

The unique structure of the sperm cell includes a haploid nucleus carrying a set of genes, an acrosome containing enzymes for fertilization, mitochondria for energy production, and a flagellum for movement.

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Acrosomal reaction

The release of digestive enzymes from the acrosome of the sperm, allowing it to break through the zona pellucida of the egg.

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Sperm-egg recognition & binding

The initial interaction between the sperm and the egg, where the sperm binds to specific receptors on the zona pellucida, ensuring the correct sperm interacts with the egg.

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ZP3 and ZP2

These are crucial proteins found in the zona pellucida of the egg. ZP3 mediates the initial sperm binding, while ZP2 facilitates subsequent binding, ensuring a stable connection.

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Follicle development stages

Follicles go through three key stages: primary, secondary, and mature (Graafian). Each stage involves structural changes and growth of the oocyte and surrounding cells.

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Secondary follicle structure

A secondary follicle has a larger oocyte, a zona pellucida, and several layers of follicular cells. It also develops an antrum - a fluid-filled cavity among the granulosa cells.

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Mature follicle (Graafian follicle)

The final stage, the mature follicle, has a larger antrum, differentiated follicular cells (corona radiata and cumulus oophorus), and the oocyte is located in the cumulus oophorus.

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Meiosis I completion in oogenesis

Only one oocyte I finishes meiosis I, producing one oocyte II (n) and one first polar body (n). The oocyte II then starts meiosis II but stops in metaphase II.

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Cytokinesis in oogenesis

Cytokinesis in oogenesis is unequal but complete, resulting in one large oocyte II and one smaller polar body, both with half the original chromosome number.

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MPF's role in oocyte meiosis

MPF (maturation promoting factor) controls the progress of meiosis in oocytes. It triggers chromosome condensation, nuclear envelope breakdown, and spindle formation.

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Metaphase II arrest in oogenesis

Oocyte II pauses in metaphase II, waiting for fertilization. This arrest is regulated by MPF and the anaphase-promoting complex.

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Regulation of oocyte meiosis

Meiosis in oocytes is tightly controlled by MPF and other factors, ensuring proper chromosome separation and the production of a mature egg cell.

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What are PGCs and where do they originate?

Primordial germ cells (PGCs) are the precursors to gametes, originating in the yolk sac during early pregnancy (around 4 weeks).

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What guides PGCs to the genital ridge?

The migration of PGCs to the genital ridge, where gonads develop, relies on the expression of IFITM1 and IFITM3 proteins in the surrounding mesoderm.

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SRY's main role

SRY, a gene on the Y chromosome, primarily regulates the expression of SOX9 during a specific time window, which is crucial for triggering male development.

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SOX9 and Sertoli cell differentiation

SOX9 is a key regulator of Sertoli cell differentiation, which are crucial for supporting sperm development, and its expression is maintained specifically in testicular Sertoli cells.

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What are epigenetic marks?

Epigenetic marks are chemical modifications to DNA that don't change the genetic sequence but influence how genes are expressed, impacting gamete development and inheritance.

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Epigenetic changes in PGCs

PGCs undergo widespread demethylation, removing epigenetic marks, then remethylation to establish new marks, ensuring proper imprinting and inheritance.

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X chromosome reactivation

In female PGCs, the inactive X chromosome is reactivated, making both X chromosomes functional, crucial for proper development.

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Histone modifications and their role in gametogenesis

Histone modifications, like methylation and acetylation, are crucial for regulating chromosome organization and gene expression in developing gametes.

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Timing of oogenesis

Oogenesis starts during embryonic development in females but ends for each oocyte after fertilization, a limited process.

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Retinoic Acid's Role

Retinoic acid, produced by the mesonephros, lung, and adrenal gland, acts as a meiosis inducer, triggering the start of germ cell division in males.

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Meiosis Inhibitor in Mouse Sertoli Cells

Sertoli cells in mice produce FGF9 and CYP26B1, which prevent meiosis from starting. CYP26B1 degrades retinoic acid, reducing its meiotic effect.

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NANOS2: Blocking Meiosis

NANOS2 is another protein that stops germ cells from entering meiosis.

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Human Testis: Meiosis Mystery

In human fetal testes, CYP26B1 is not expressed, making the mechanism that prevents early meiosis unclear.

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Spermatogonia: The Start

These undifferentiated germ cells multiply through mitosis during the proliferation phase.

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Growth Phase: Transformation

Secondary spermatogonia grow and develop into primary spermatocytes during the growth phase.

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Spermatogonial Syncytium

Cytoplasmic bridges between spermatogonia ensure synchronized sperm production within a seminiferous tubule.

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Akap82 protein's function

The Akap82 protein plays a crucial role in forming the tail of sperm cells.

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Cytokinesis in spermatogenesis

After cell division, the two resulting cells (precursors to male sex cells) remain connected by cytoplasmic bridges that eventually dissolve during the late stages of sperm development.

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Spermiogenesis: Tail formation

During spermiogenesis, the microtubules in the sperm cell elongate, forming a tail structure responsible for movement.

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Spermiogenesis: Acrosome

The acrosome, formed from the golgi complex, is a specialized lysosome containing digestive enzymes (hydrolases) that help the sperm penetrate the egg.

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Spermiogenesis: Organelle rearrangement

During this stage, organelles in the sperm cell are relocated and rearranged to optimize for sperm function and motility.

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Ca2+ surge in the egg

A crucial signal triggered by sperm entry, initiating the completion of meiosis in the oocyte and prompting exocytosis of secretory vesicles from the egg.

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Cortical Reaction

A crucial process triggered by Ca2+ in the egg. Enzymes released from cortical granules harden the Zona pellucida, preventing further sperm entry and ensuring monospermy.

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Synkaryon

The single nucleus formed by the fusion of male and female pronuclei after fertilization, resulting in a diploid zygote with a complete set of chromosomes.

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Cleavage

A series of rapid mitotic cell divisions without cell growth that occurs after fertilization, transforming the zygote into a multicellular embryo.

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Importance of Fertilization

Fertilization is a crucial event that triggers changes in the egg's cytoplasm, re-establishes the diploid chromosome number, and mixes paternal and maternal chromosomes.

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What are acrosin, hyaluronidase, and neuraminidase?

These are enzymes found within a sperm's acrosome, essential for breaking through the protective layers of the egg (zona pellucida) during fertilization.

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What is nuclear morphogenesis?

This process involves the nucleus of the sperm changing shape from round to oval, becoming denser, and undergoing chromatin condensation. Sperm-specific histones are also produced.

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What is the function of the sperm's flagellum?

The flagellum, a tail-like structure, is composed of microtubules that help the sperm move in a whip-like motion, propelling it towards the egg.

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What is the significance of mitochondria fusion in sperm?

The mitochondria within the sperm fuse together, forming a spiral around the tail, providing the energy needed for the sperm's movement.

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What is an acrosomal reaction?

This is the process where the sperm releases digestive enzymes from its acrosome, allowing it to break through the outer layer (zona pellucida) of the egg.

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What is sperm-egg recognition & binding?

This is the initial interaction where the sperm finds its target egg and binds to specific receptors in the egg's zona pellucida.

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What are ZP3 and ZP2's roles in fertilization?

These are proteins within the egg's zona pellucida. ZP3 mediates the initial sperm binding, while ZP2 ensures further binding stability.

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What happens when the sperm and egg membranes fuse?

The plasma membranes of the sperm and egg merge, allowing the sperm cell to enter the egg, beginning the process of fertilization.

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Study Notes

Gametogenesis

  • Gametogenesis is the development of haploid sex cells (sperm and egg) from diploid organisms through meiosis.
  • Oogenesis is the process of female gamete formation.
  • Spermatogenesis is the process of male gamete formation.

Origin of Gametes

  • Primordial germ cells (PGCs) arise in the yolk sac during approximately the 4th week of pregnancy.
  • Alkaline phosphatase is a marker for primordial germ cells (PGCs).
  • During weeks 4-6 of pregnancy, PGCs migrate to the genital ridge, which is a bisexual gonad.
  • Early PGC migration depends on IFITM1 and IFITM3 expression in surrounding mesoderm.

Formation of Spermatogonia and Oogonia

  • Y chromosome's SRY gene drives testis development, activating SOX9, a master regulator of Sertoli cell differentiation.
  • In females, the absence of SRY leads to ovary development.
  • Germ cells, in both males and females, are imprinted differently.

Epigenetic Regulation of Gametogenesis

  • Germ cell genes, but not somatic cell genes, are passed to the next generation.
  • Imprinted marks in the zygote are erased during germ cell development.
  • Developing gametes are imprinted with proper marks according to the developing embryo's sex; these marks are retained in somatic cells.
  • Widespread genome-wide demethylation and remethylation occur in PGCs.

Periods of Oogenesis

  • Proliferation period: approximately the third month of development, producing oogonia, which increase in number.
  • Growth period: from fourth to sixth month, where oogonia become primary oocytes.
  • Maturation period: primary oocytes remain arrested in prophase I until puberty.

Timing of Gametogenesis

  • Males: commences at puberty and continues throughout life.
  • Females: begins in embryonic life and completes for each oocyte after fertilization.

Spermatogenesis

  • Spermatogenesis starts at puberty.
  • Spermatogonia undergo mitosis to increase their number.
  • Secondary spermatogonia develop into primary spermatocytes.
  • Meiosis I produces secondary spermatocytes, followed by meiosis II to produce spermatids.
  • Spermatids undergo spermiogenesis to form mature sperm cells.
  • Spermatogenesis continues throughout life.

Abnormal Gametes

  • Azoospermia: absence of sperm in semen.
  • Oligozoospermia: low sperm count (below 20 million spermatozoa per ml).
  • Sertoli cell-only syndrome: only Sertoli cells found in seminiferous tubules.
  • Kartagener syndrome: hereditary condition affecting sperm motility.

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Description

This quiz covers the process of gametogenesis, including the formation of sperm and eggs through meiosis. It delves into spermatogenesis and oogenesis, the origin of gametes, and the role of primordial germ cells. Additionally, the quiz discusses the epigenetic regulation involved in these processes.

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