Germ Cells and Development Quiz

Questions and Answers

What is the initial source of gametes in embryos?

Primordial germ cells (PGCs) originate from the epiblast.

During which developmental process do germ cells migrate to the yolk sac wall?

Germ cells migrate during gastrulation.

What are teratomas and what do they originate from?

Teratomas are tumors that originate from pluripotent cells, which can differentiate into various tissue types.

What two main processes do germ cells undergo during gametogenesis?

Germ cells undergo meiosis and cytodifferentiation during gametogenesis. Signup and view all the answers

When do primordial germ cells arrive at the developing gonads?

PGCs arrive at the developing gonads by the end of the fifth week. Signup and view all the answers

What is the primary role of paracrine signaling in cellular communication?

Paracrine signaling facilitates the induction, responsiveness, and intercommunication among cells. Signup and view all the answers

What are the components involved in a paracrine signaling pathway?

A paracrine signaling pathway includes a signaling molecule (ligand), a receptor, and the activation of downstream signaling components. Signup and view all the answers

How does a receptor typically function after a ligand binds to it?

Upon ligand binding, the receptor activates its cytoplasmic domain, which often initiates enzymatic activity. Signup and view all the answers

What is the difference between paracrine and juxtacrine signaling?

Paracrine signaling involves the diffusion of signaling molecules to nearby cells, while juxtacrine signaling involves direct cell-to-cell contact. Signup and view all the answers

What role do extracellular matrix ligands play in juxtacrine signaling?

Extracellular matrix ligands serve as signaling molecules that facilitate communication between cells and their surrounding environment. Signup and view all the answers

Study Notes

Germ Cells

Fertilization combines male sperm and female oocyte to form a zygote.
Primordial germ cells (PGCs) arise in the epiblast during the second week.
PGCs migrate through the primitive streak into the yolk sac and then to the developing gonads by the end of the fifth week.
Gametogenesis involves meiosis for chromosomal reduction and cytodifferentiation for maturation.

Clinical Correlations

Teratomas are tumors from pluripotent cells differentiating into various tissues like bone and muscle.
Pluripotent germ cells or mislocated PGCs could cause teratomas.

Cellular Signaling

Essential for induction, competence, and intercellular communication.
Paracrine Interactions: Involve proteins that diffuse to interact with other cells, utilizing diffusible proteins.
Juxtacrine Interactions: Involve direct interactions between adjacent cells without diffusible proteins; utilize growth and differentiation factors (GDF).

Signal Transduction Pathways

Paracrine signaling employs transduction pathways activating/blocking inhibitors (e.g., hedgehog signaling).
Involves a signaling molecule (ligand) and a receptor spanning the cell membrane.
Ligand binding activates the cytoplasmic domain of the receptor, typically a tyrosine kinase, leading to protein phosphorylation and a cascade of protein interactions which activate transcription factors influencing gene expression.

Mitosis Overview

Mitosis produces two genetically identical daughter cells.
Major phases include:
- Prophase: Chromosomes visible as distinct units.
- Prometaphase: Nuclear envelope breaks down, spindle fibers attach to centromeres.
- Anaphase: Sister chromatids separate and move to opposite poles.
- Telophase: Daughter chromosomes reach poles, spindle fibers disappear, nuclear envelopes reform.

Meiosis and Genetic Variability

Crossing over during meiosis enhances genetic variability through chromatid exchange, leading to the formation of chiasmata.
Meiosis results in haploid cells, restoring the diploid number upon fertilization.
Polar bodies are byproducts of oocyte division and do not participate in fertilization.

Gametogenesis Processes

Oogenesis: The process from oogonia to mature oocytes begins before birth.
Spermatogenesis: Starts at puberty; spermatogonia develop into sperm in seminiferous tubules.

Chromosomal Characteristics

Normal human somatic cells contain 46 chromosomes (diploid); gametes contain 23 chromosomes (haploid).
Chromosomal abnormalities contribute significantly to congenital defects and spontaneous abortion, with about 50% of conceptions resulting in miscarriage due to such anomalies.

Maturation of Gametes

In oogenesis, primary oocytes undergo divisions, resulting in a single mature oocyte.
In spermatogenesis, four viable sperm are derived from each primary spermatocyte during meiotic divisions.