Early Embryogenesis Flashcards
What are gametes derived from?
Germ cells, they undergo meiosis to give rise to haploid gametes
Define haploid
Only one copy of each chromosome
Define diploid
Two copies of each chromosome present
Sperm structure
Acrosomal vesicle at head
Nucleus
Lots of mitochondria
Flagellum
Stages of fertilisation
- Binding of sperm to zona pellucida
- Acrosomes reaction - acrosomes released from vesicles to break down bona pellucida
- Penetration through bona pellucida
- Fusion of plasma membranes
- Sperm nucleus enters egg cytoplasm
What is polyspermy?
Fertilisation of an egg by multiple sperm entering as the same time
How is polypsermy usually prevented?
- Change in membrane potential after one sperm enters
- Cortical reaction
What is the cortical reaction?
Formation of the fertilisation membrane and hyaline layer –> prevents other sperm from binding to the egg plasma membrane
Egg activation - after fertilisation
Release of calcium ions
Ca2+ travels across resulting in the completion of meiosis
- Both necessary and sufficient for egg activation
Which ion is involved in egg activation?
Ca2+
Can cells become polarised and divide asymmetrically during development?
Yes
Difference between blastula and blastocyst
Blastocyst has the embryoblast/inner cell mass
What is cleavage?
Rapid and synchronous division of cells with no overall growth to form ball of cells - blastula
3 examples of different cleavage patterns
- Holoblastic
- Meroblastic
- Superficial
Which organism/s have a holoblastic cleavage pattern?
Mouse, human, C. elegans
Which organism/s have a meroblastic cleavage pattern?
Zebrafish, chick
Which organism/s have a superficial cleavage pattern?
Drosophila
Which phase of the cell cycle is not present in the earl embryo?
The G phase
Zygotic genome activation
During cleavage, zygotic genome is transcriptionally silent and embryo uses maternal supply of nucleotides and histones to replicate DNA content
What happens due to zygotic genome activation?
- Cell cycle slow
- Cell cycle becomes asynchronous
- Cell movement begins
How does the embryo replicate DNA content during cleavage?
Uses maternal supply of nucleotides and histones
