Gametogenesis Flashcards
What 2 main cell types are found in an organism?
Somatic cells (body cells)
Germ cells (sex cells)
What is the importance of germ cells?
Meiosis
Gametogenesis
Genes may be transmitted
What is the importance of somatic cells?
Mitosis
Keeps germ cells alive
DNA here will be lost
Where are germ cells found?
Sex organ (gonads) - primary reproductive organ
What is the male reproductive organ?
Testes
What is the female reproductive organ?
Ovaries
Where are the germ cells produced?
Sperm cells in testes
Oocytes in ovaries
Where in the testes are the sperm cells produced?
Within seminiferous tubules
Where in the ovaries are oocytes produced?
Oocytes contain within follicles (primordial through to Grafian)
How are germ cells separated from somatic cells?
Different time points for different organisms.
Somatic cells can function as stem cells and differentiate into germ cells throughout life.
Example - Tunicates, Crideria and planeria
Germ cells form at specific time and early on development.
Migrate to gonads later on development.
How are germ cells separated from somatic cells?
Different time points for different organisms.
Somatic cells can function as stem cells and differentiate into germ cells throughout life.
Example - Tunicates, Crideria, and planaria
Germ cells form at a specific time and early on in development.
Migrate to gonads later on in development.
What are the 4 proteins that define germ cells?
Vick - Vasa
Nicked - Nanos
Ten - Tudor
Pizzas - Piwi
- highly conserved
Expression of the 4 proteins defines how these germ cell form.
What is the function of vasa proteins?
Bind to mRNA
Increase translation efficiency of germ cells specific efficiency
What is the function of nanos proteins?
Bind to mRNA
Decreases translation efficiency specific messages
Present in somatic cells ( mesoderm/ectoderm/endoderm)
What is the function of Tudo + Piwi proteins?
Silence gene transcription
Classical transcription factors
Where does pre-determined (autonomous) formation occur?
Nematodes
Insect
Fish
Frogs
Where is induced germ cell formation occur?
In mammals
What is unique about pre-determined (autonomous) formation?
No external signal
Germ plasm
Concentration of vasa proteins
Cell fate restricted by germ plasm
An example of pre-determined (autonomous) formation?
C-elegans (worms)
P cells- P1 to P4
Concentrated in vasa proteins
Destroying P cells- > No germ cells -> Infertile
What is germ plasm?
Granule containing cytoplasm
Not present in mammals
How is germ cell prevented from differentiating into somatic cells?
Inhibitors of gene transcription
Summaries pre-determined germ cell formation?
Sperm fertilises egg
Embryo divides
Early development -small group of cells - earmarked = pre-determined
These become germ cells
What is unique about induced germ cell formation?
Mammals
Germ cells form later
Vasa/nanos/tudor/ piwi proteins not present in egg
Expression is induced by paracrine molecules from neighbouring cells
What is the strongest evidence against pre-determination in humans?
Identica twins
2 cell stage
Late division of embryo
If pre-determined -> one will be infertile
We don’t see that
