Gametogenesis and Fertilisation Flashcards
What term is given to germ cells that move into the testes?
Spermatogonia.
What term is given to germ cells that move into the ovaries?
Oogonia.
Define the term primordial germ cell (PGC).
The precursors to gametes which later develop, via meiosis, into sperm or egg cells.
Where do primordial germ cells originate (PGCs)?
In the extra-embryonic tissue.
Where do PGCs migrate (in terms of inside the embryo) and what route do they take?
They migrate into the embryo via the gut and into the genital ridge.
What does the genital ridge eventually develop into?
The somatic cells of the gonad.
What is the importance of meiosis?
It introduces genetic variability.
How do PGCs multiply during migration?
Via mitosis.
How are spermatocytes produced?
Spermatogonia multiply via mitosis to produce spermatocytes.
Spermatocytes enter meiosis. After meiosis what is produced?
Haploid spermatids connected by cytoplasmic bridges.
Define synctial cells.
Fused cells with multiple nuclei such as spermatids before differentiation.
Why is cytokinesis not completed during Meiosis II?
To ensure the haploid spermatids mature in synchrony.
What do spermatids differentiate into?
Spermatozoa.
How many spermatozoa are produced from each spermatocyte?
Four.
What are the stages of male gametogenesis?
PGC, spermatogonia, spermatocytes, spermatids, spermatozoa.
What changes occur during spermiogenesis (spermatids differentiating into spermatozoa)?
Golgi develops into acrosomal cap.
Flagellum develops.
Mitochondria coalesce at flagellum.
Cytoplasmic bridges are lost.
What is contained within the acrosome?
Lytic enzymes to digest proteins, lipids and carbohydrates.
What is the axoneme?
A cytoskeletal structure that forms the core of the flagellum.
How is dynein involved in sperm motility?
It is a motor protein that uses energy from ATP hydrolysis to move microtubules past one another.
When does meiosis occur during spermatogenesis?
Before differentiation.
When does meiosis occur during oogenesis?
After differentiation.
How are primary oocytes produced?
Oogonia enter meiosis and arrest in Prophase I to form primary oocytes.
When does Meiosis I complete?
Upon ovulation.
What is produced during Metaphase II?
Secondary oocytes.
When does Meiosis II complete?
After fertilisation.
How many ova and polar bodies are produced from each primary oocyte?
1 ova and 2 polar bodies.
What surrounds a mammalian oocyte?
The zona pellucida.
What is the zona pellucida?
A translucent layer of 3 glycoproteins: ZP1, ZP2 and ZP3.
What is the significance of the ZP3 glycoprotein?
It is the sperm receptor and ensures species specificity.
What are cortical granules?
Organelles derived from the golgi apparatus. They contain proteases and glycosidases.
Why are cortical granules important?
They prevent polyspermy (multiple fertilisations).
What is the first stage of fertilisation?
Sperm binding to zona pellucida.
What is the second stage of fertilisation?
The acrosome reaction.
What is the third stage of fertilisation?
Penetrating the zona pellucida.
What is the fourth stage of fertilisation?
The fusing of membranes.
What is the fifth stage of fertilisation?
Sperm nucleus and contents enter the cell cytoplasm.
What surrounds the zona pellucida?
Cumulus cells.
Name the recognition protein for ZP3.
Sperm galactotransferase (GalT).
What does GalT clustering trigger during fertilisation?
G protein activation and a change in membrane potential.
What is the acrosomal reaction?
Calcium-mediated exocytosis of the
acrosomal vesicle being initiated.
What 3 processes occur in the oocyte after fertilisationi?
- Exocytosis of cortical granules.
- Completion of Meiosis II.
- Metabolic activation.
What does sperm entry trigger the release of? What organelle is the source of this?
Calcium ions from the endoplasmic reticulum.
What does the sperm provide?
A haploid genome and a centriole.
What does the ovum provide?
A haploid genome, mitochondria (and other organelles) and mRNAs/proteins for early development.
