Practice question

Chick oocyte telolecithal with massive yolk accumulates at vegetal pole, cytoplasm including nucleus, mitochondria and maternal RNAs concentrates at animal pole forming blastodisc. Cleavage restricted there produces area pellucida and opaca atop yolk. This polarized arrangement persists through laying, embryo developing from animal-most disc while yolk provides nutrition vegetally. Position contrasts vegetal pole which is yolk, equator lateral, posterior pole defined later after axis formation. Therefore blastodisc situated at animal pole analogous to zebrafish blastoderm at animal pole of heavily yolky egg. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.