Practice question

Meroblastic cleavage occurs in eggs with dense yolk concentrated at vegetal pole that prevents complete division. Only cytoplasmic disc at animal pole undergoes cleavage, forming blastoderm sitting on yolk mass. Birds such as chickens and reptiles possess telolecithal eggs with massive yolk for external development, necessitating meroblastic discoidal pattern. Mammals and frogs have holoblastic cleavage because isolecithal or mesolecithal eggs contain less yolk, allowing cleavage furrows to bisect entire egg. Holoblastic cleavage creates smaller equal or unequal blastomeres, while meroblastic supports large nutrient stores required for oviparous development.