Soft keratins, or cytokeratins, are found in epithelial cells and make up the skin.

TLS Online TPP Program

#Id: 7597

#Unit 5. Developmental Biology

The zona pellucida in mammals plays a role analogous to that of the vitelline envelope in invertebrates; the zona, however, is a far thicker and denser structure than the vitelline envelope

TLS Online TPP Program

#Id: 7598

#Unit 5. Developmental Biology

The mouse zona pellucida is made of three major glycoproteins—ZP1, ZP2, and ZP3

TLS Online TPP Program

#Id: 7599

#Unit 5. Developmental Biology

The human zona pellucida has four major glycoproteins— ZP1, ZP2, ZP3, and ZP4

TLS Online TPP Program

#Id: 7600

#Unit 5. Developmental Biology

The mammalian egg encounters a heterogeneous population of sperm. Some sperm have undergone the acrosome reaction in or near the cumulus, whereas others have not. The egg have pathways for accepting both types of capacitated sperm.

TLS Online TPP Program

#Id: 7601

#Unit 5. Developmental Biology

In one pathway, sperm that have undergone the acrosome reaction bind directly to ZP2

TLS Online TPP Program

#Id: 7602

#Unit 5. Developmental Biology

In 2nd pathway, sperm with intact acrosomes become bound to ZP3, which causes the acrosome reaction, and the sperm binding is then transferred to ZP2