Lecture 4 Flashcards
1st trimester
Most organs begin to form
2nd trimester
Limbs elongate and fetus moves
Nervous system develops rapidly
3rd trimester
Grows rapidly and most organs begin to function
Mechanism for Asymmetric Cell Division
- Establish cell polarity (apical vs basal)
- Orient mitotic spindle
- Localize cell fate determinants
Blastomeres
Cells derived from cleavage
- different among animals
—> complete cleavage (frog)
—> incomplete (fish and bird)
—> superficial cleavage (fruit fly) (single cell with many nuclei called a syncytium)
Increase cell number without increasing cell mass
Maternal Effects
Organism shows phenotype expected from genotype of mother regardless of their own
This is often because the mother supplies mRNAs or proteins to the egg
Ovary Nurse Cells
Deposit different regulatory molecules into the eggs along A-P and D-V axes
Homeotic Genes
Define role of each segment
Segment Polarity Genes
Determine the boundaries and A-P orientation of each segment
Nuclear gradient is caused by?
High threshold genes (mesoderm) vs. Low threshold genes (neural ectoderm)
Amphibian Embryonic Axes
Sperm entry: ventral / dorsal
Anterior (animal pole) / Posterior (vegetal pole)
Animal has more cytoplasm
Head mesoderm contains
Facial muscles
Axial Mesoderm contains
Notochord
Paraxial mesoderm
Somites (muscles, spine, ribs)
Intermediate mesoderm
Kidneys, gonads
