Early Embryogenesis Flashcards
What are gametes?
Specialized cells that are derived from germ cells that undergo meiosis to form haploid gametes
What is an oocyte?
A large cell that contains maternal stores (RNA and protein) to support growth through the early stages of development where there is no zygote transcription.
What does a sperm have to penetrate to enter the egg?
Zona pallucida
How is polyspermy prevented?
Cortical granules are released from the egg which causes the vitelline membrane to rise from the egg. This forms the fertilisation membrane and hyaline layer. And membrane depolarisation.
How is the egg activated?
Calcium ions are released when the sperm penetrates the egg, which activates proteins that control the cell cycle, which causes the egg to complete meiosis.
What is ZGA and when does it occur?
Zygotic genome activation. This occurs when all maternal stores of RNA and proteins run out, so zygote transcription is initiated.
What is meroblastic division/ cleavage and what organism does it occur in?
Incomplete division of cells so the cytoplasm is shared. In the fish.
What is holoblastic division/cleavage and what organism does it occur in?
complete cell division during cleavage, so the zygote is divided into blastmeres. In humans.
What is superficial cleavage? In what organism does it occur?
Division of the nuclei without the formation of cells. In drosophila.
Give 2 ways in which cells become different (differentiated)
Cell-cell signalling and cytoplasmic component segregation.
What is a blastula?
Hollow ball of cells (blastomeres) enclosing a blastocoel.
What is a morula?
A solid ball of cells (blastomeres) resulting from the cleavage of a fertilised ovum.
What are the 4 stages in cell-cell signalling?
- Activation of a cell surface receptor7
- intracellular transduction of signals
- activation of transcription factors
- expression/transcription of new genes
