Animal Development 2024 PDF

Animal Development Mohd Ridwan Abd Rahman Learning objectives 1. Describe the process of fertilisation 2. Describe the process of embryogenesis (Cleavage, Gastrulation, Organogenesis) Animal Development Phases in animal development EMBRYONIC DEVELOPMENT...

Animal Development Mohd Ridwan Abd Rahman Learning objectives 1. Describe the process of fertilisation 2. Describe the process of embryogenesis (Cleavage, Gastrulation, Organogenesis) Animal Development Phases in animal development EMBRYONIC DEVELOPMENT Sperm Zygote Adult Egg frog Metamorphosis Blastula Larval Gastrula stages Tail-bud embryo Fertilization to Embryogenesis Research on fertilization began in earnest in twentieth century when biologist studied the sperm-egg reaction of sea- urchins. Sea urchins are models for the study of the early development of deuterostomes Sea urchins eggs are fertilised externally. 1) Fertilization 1. Sperm contact with egg 2. Acrosomal reaction: when sperm exposed to egg’s jelly coat (zona pellucida), the sperm’s acrosome discharges its contents by exocytosis 3. Enzymes enable the acrosomal process to penetrate the egg’s jelly coat. The tip of acrosomal process adheres to the vitelline layer just external to the egg’s plasma membrane 4. The sperm & egg plasma membranes fused 5. A single sperm nucleus enter the egg’s cytoplasm. ▪ Ca2+ channels in the egg’s plasma membrane opens. ▪ A wave of ion release starts at the point of sperm entry and propagates throughout the egg. 6. The cortical granules responded to the Ca2+ signal by fusing with the membrane and releasing their contents (include proteases) to the exterior ▪ proteases digest the egg-cell receptor for sperm (prevents any new sperm from binding to the egg surface) EXPERIMENT The influx of water 10 sec after 25 sec 35 sec 1 min fertilization 500 m causes the envelope RESULTS matrix to lift away from the cell, forming fertilization envelope that keeps additional sperm from contacting the egg’s 1 sec before 10 sec after 20 sec 30 sec fertilization fertilization 500 m plasma membrane, CONCLUSION avoiding polyspermy. Point of sperm Spreading Fertilization nucleus wave of Ca2+ envelope entry 2) Cleavage Rapid cell division that take place immediately after fertilization In most animals, cleavage partitions the egg cytoplasm without additional cell growth taking place ▪ The cytoplasm present in the egg is divided into a larger and larger number of smaller and smaller daughter cells. The cells that are created by cleavage divisions are called blastomeres (“bud-part). Continued cleavage produces the morula. Cleavage is complete when blastocoel is formed. The embryo consists of a mass blastomere cells are called a blastula (“little sprout, bud”) 3) Gastrulation Rearranges the embryo into a triploblastic gastrula. ▪ extensive and highly organized cell movements radically ▪ embryonic germ layers are the Ectoderm (“outer skin”), mesoderm (“middle skin”) & endoderm (“inner skin”). PROTOSTOMES DEUTEROSTOMES Mollusks e.g squids, snails, slugs Echinoderms e.g starfish, sand-dollars Annelids e.g leeches, earthworms Chordates e.g mammals, birds) Arthropods e.g insects CLEAVAGE FATE OF BLASTOPORE 4) Organogenesis organ-origin”, is a process of tissue and organ formation that begins once gastrulation is complete (embryonic layers are in place) The three germ layers give rise to specific organs and organ system Thank You