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#egg structure

2 public questions tagged with this topic.

The vegetal pole in amphibian eggs contains:

Amphibian eggs exhibit pronounced animal-vegetal polarity that influences cleavage. Animal hemisphere contains little yolk, abundant mitochondria, ribosomes, and divides rapidly into small micromeres that contribute mainly to ectoderm and nervous system. Vegetal hemisphere accumulates dense yolk platelets, glycogen, lipids, and maternal mRNAs such as VegT and Vg1, slowing cleavage and producing large macromeres. Heavy yolk physically hinders contractile ring constriction, lengthening cell cycle vegetally. This gradient creates unequal blastomere sizes, partitions endoderm determinants vegetall

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 2: Vegetal yolk distribution and cleavage retardation.

The micropyle in Drosophila eggs primarily functions to:

Insect eggshell includes thick chorion and inner vitelline membrane impermeable to sperm. A single micropyle acts as exclusive portal, permitting only one sperm to traverse thick envelopes. Upon fertilization, vitelline membrane undergoes rapid crosslinking and hardening mediated by calcium-dependent enzymes, blocking additional sperm passage. The combination of single narrow canal and fast envelope modification provides structural polyspermy prevention. Since Drosophila eggs normally activate independently of fertilization before sperm entry, preventing multiple sperm pronuclei is critical fo

Ref: NCBI Bookshelf, Developmental Biology: Fertilization - polyspermy prevention in insects.