Question

1. How can you tell the difference between meroblastic and holoblastic cleavage? Why does meroblastic cleavage occur? Out these animals (fish, birds, mammals and frogs) which have meroblastic cleavage and which had holoblastic cleavage?

2. When does Epiboly occur? Which tissue layer is produced? Describe what happens in Epiboly and give an example. Describe what occurs in involution? What tissue layer is produced? And give an example of involution from class?

3. What is the fate of each germ layer (Ectoderm, Mesoderm, Endoderm)? How does ectoderm become both skin and brain? What are Mesenchyme cells? What is neurulation? Compare and contrast primary and secondary neurulation? How are cadherin molecules important?

Answer 1

1. Meroblastic cleavage ; It is an incomplete or partial cleavage that it cannot penetrate the egg completely . Holoblastic cleavage , where the division is complete and seperate . Meroblastic cleavage , where the large amount of the egg yolk in the fertilized egg cell , the holoblastic cleavage produces the isolecithal and meroblastic clevage produces the teloblastic cleavage. Birds , fishes have the meroblatic cleavage . frogs have holoblatic cleavage .

2. Epiboly ; It is a cell movement that occurs in early embryo at the same as gastrulation, epiboly produces the primary germlayers . Involution a tissue rolls inward to form the underlying layer via bulk movement of the tissue . Tissue layers produced endoderm .

3. A germ layers is the primary layer of the cell that form during the embryogenesis .The ectoderm give rise to the central nervous system ,peripheral nervous system ,sensory epithelia of the eye ,ear ,nose , th epidermis and its appendages ,ectoderm development is called neuralation in regard to nervous system. the neural crest develop into the peripheral nervous system , adrenal medulla , melanocytes , facial cartilage ,neural tube develops into the brain ,spinal cord ,posterior pitutary neuron , retina. Mesenchymal cells are the multipotent stromal cells that can be diffrentaited into the different typesof the cells include osteoblasts , chondrocytes , myocytes and adipocytes .

Neuralation is the folding process in the vertebrates which includes the transformation of the neural plateinto the neural tube . primary neuralation is a process the neural plate creases inward until edge come in contact and fuse .Secondary neuralation where the tube forms by the hollowing out of the interior of the solid precursor . cadherins molecules are the type 1 the transmemberane proteins ,they play a important role in adhesion forming the adhesion junctions to bind cells within tissue togather .