Concepts of Developmental Biology

Developmental Biology is an important link between almost all biological sciences, and is assuming more and more importance in fields such as machine and agriculture. Molecular biology has began fulfilling its long anticipated role of linking genetics and embryology and many questions of embryology that had lain dormant for decades have been taken up with new molecular tools and strategies. While our knowledge of the molecular aspects of development has so drastically increased during this time, our applications of developmental phenomenon in evolution and ecology has also expanded. Cleavage refers to the early cell divisions that occur as a fertilized egg begins to develop into an embryo. In those cases where eggs are provided with the large concentrations of yolk, the cleavage furrow fails to bisect the entire egg. This is the meroblastic or partial cleavage. The large concentrations of yolk prohibit cleavage in all but a small portion of the egg cytoplasm. There are two types of meroblastic cleavage divisions. The placenta is a temporary fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations, and is an important endocrine organ producing hormones that regulate both maternal and fetal physiology during pregnancy. The aim is to enthuse the reader with this active and exciting area of research and to lay a solid foundation on which further study of its various facts may be based.