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Animal Development Features Shared By Most Animals • At early stages of development, all vertebrate embryos are very similar • Major stages of embryonic development are: fertilization, cleavage, gastrulation, organogenesis • The zygote undergoes a series of mitotic divisions known as cleavage which produces a blastula (often takes the form of a multicellular hollow ball) in most animals • Gastrulation (involving the infolding of embryonic cells forming concentric germ layers that become the various tissues and organs as development continues ; the formation of the two-layered, cup-shaped embryonic stage) occurs after the blastula has formed; during this process the embryonic forms of adult body tissues are produced Development and Body Plan Fertilized egg (one cell) → cleavage begins → two cell stage → four cell stage → → → → → → Morula (latin for mulberry – solid ball of embryonic cells) → Blastula "Blasted Out” (ball of cells with fluid filled center called blastocoel) → Gastrulation (folding in to form "germ layers") More Features Shared By Most Animals • Highly differentiated body cells which are organized into tissues, organs, and organ systems for such specialized functions as digestion, internal transport (circulation), gas exchange, movement, coordination, excretion, and reproduction • Nervous tissue (impulse conduction) and muscle tissue (movement) are unique to animals • Reproduction is typically sexual with flagellated sperm fertilizing non-motile egg to form diploid zygotes (a diploid stage dominates the life cycle) AP Embryology Crash Course in Animal Development Bonus – Name Embryo “E” Mature Sperm Anatomy • The acrosome vesicle contains the enzymes required to digest its way though the ovum wall. • Haploid nuclei (n=23) containing the paternal chromosome set • The 'mid-section' of the sperm contains many mitochondria which synthesis ATP to provide the energy for the movement of the tails structure. The Egg • The haploid nuclei (arrested at metaphase II ) sits inside a cell with a large volume of cytoplasm (yolk). • During follicle development unequal division of the cell during meiosis produces the 1st polar body that can be seen outside the plasma membrane. This will not develop. • The Zona pellucida surrounds the structure and is composed of glycoproteins. With the cortical granules they will be involved in the acrosome reaction at fertilization. • Around the outside are the follicular cells. Acrosome and Cortical Rxns Fertilization: • In all species the egg cells release a specific signal usually a polypeptide that acts as a signal to the sperm cell to fertilize the egg and not other cells. • The signals appear to be species specific and are one mechanism that prevents hybridization although this is probably more important in aquatic species rather than humans. • Other important events include the restoration of the diploid number (n+n=2n) and mechanisms that prevent polyspermy Acrosome and Cortical Rxns Fertilization of the human egg (a) The cumulus is a thick loose grouping of cells in a gelatinous matrix. The sperm cell must penetrate this mass to reach the zona pellucida, a glycoprotein matrix surrounding the egg plasma membrane. (b) Contact between the zona pellucida and proteins in the sperm cells membrane trigger a the acrosome reaction. (c) The acrosome vesicle fuses with the sperm plasma membrane and releases enzymes that digest a path through the zona pellucida. (d) The membrane of the sperm cell and the ovum fuse together. This causes a release of Ca2+ from the endoplasmic reticulum. (e) The cortical vesicle fuse with the plasma membrane releasing enzymes that destroy the sperm binding proteins on the zona pellucida. This prevents polyspermy. The release of Ca2+ also activate meiosis and prepare the cell for completion of reduction division , MII and cell division The acrosomal and cortical reactions Even More Features Shared By Most Animals • The zygote undergoes a series of mitotic divisions known as cleavage which produces a blastula (often takes the form of a multicellular hollow ball) in most animals Early embryonic development The HOX Genes 1. 2. 3. 4. The transformation of a zygote to an animal of specific form depends on the controlled expression in the developing embryo of special regulatory genes called Hox genes. These genes regulate the expression of other genes. Many of these Hox genes contain common “modules” of DNA sequences, called homeoboxes. Only animals possess genes that are both homeoboxcontaining in structure and homeotic in function. a. All animals, from sponges to the most complex insects and vertebrates have Hox genes, with the number of Hox genes correlated with complexity of the animal’s anatomy. Three Germ Layers A germ layer is a layer of cells during fetal development that all have similar fates. a. Ectoderm 1) covers the surface of an embryo 2) • Forms the nervous system and epidermis i.e. the "attractoderm"- anything that would attract you to someone else- skin, brain, nervous tissue and sensory organs such as eyes etc. Three Germ Layers b) Endoderm 1) innermost germ layer which lines the archenteron (primitive gut) 2) Forms the lining of the digestive and respiratory systems, bladder lining, and the liver • i.e. the "endernal" organs and anything branching off the digestive, respiratory system Three Germ Layers c. Mesoderm 1) located between the ectoderm and endoderm in tripoblastic animals 2) • muscular, circulatory (vascular), excretory (urogenital), skeleton, connective tissue, etc. i.e. the "means-o-derm"- the means of getting from one place to another The “Body Cavity” • Fluid-filled cavity that forms within the mesoderm of an animal is called a coelom a. a “true” body cavity is lined with a layer of mesoderm surrounding both the inside of the body wall and the internal organs b. The structure and development of the coelom is an important character for recognizing major groups of animals. Differentiation and the Fate of Cells Cytoplasmic Factors in Determining the Fate of Cells Acoelomates a. Acoelomate - no body cavity is present between the digestive tract and the outer body wall 1) This area is filled with cells Body plans of the bilaterally symmetrical organisms Body plans of the bilaterally symmetrical organisms Body plans of the bilaterally symmetrical organisms Pseudocoelomates b. Pseudocoelomate - a fluid filled body cavity separates the digestive tract and the outer body wall 1) The cavity (pseudocoelom) is not completely lined with mesoderm therefore considered a “false” cavity Body plans of the bilaterally symmetrical organisms Body plans of the bilaterally symmetrical organisms Coelomates c. Coelomate - fluid-filled body cavity completely lined with mesoderm (a true body cavity) 1) The coelom separates the digestive tract from the outer body wall 2) Mesenteries (tissues) connect the inner and outer mesoderm layers and suspend the internal organs in the coelom 3) fluid cushions the organs to prevent injury 4) internal organs can grow and move independently of the outer body wall 5) serves as a hydrostatic skeleton in soft-bodied coelomates such as earthworms Body plans of the bilaterally symmetrical organisms Body plans of the bilaterally symmetrical organisms Body plans of the bilaterally symmetrical organisms Body plans of the bilaterally symmetrical organisms The “Body Cavity” – A Comparative Look Introduction to Animals Crash Course in Animals Part 1 Crash Course in Animals Part 2 Protostome-Deuterostome Dichotomy Coelomate phyla can be divided into two distinct evolutionary lines, protostomes and deuterostomes Protostome-Deuterostome Dichotomy Protostomes and Deuterostomes are distinguished by developmental differences which include cleavage patterns, coelom formation and the fate of the blastopore (first opening of the archenteron which forms during gastrulation) A comparison of early development in protostomes and deuterostomes A comparison of early development in protostomes and deuterostomes - Coelomate phyla can be divided into two distinct evolutionary lines, protostomes and deuterostomes Protostomes Deuterostomes Major animal groups mollusks, annelids, arthropods echinoderms and chordates Cleavage spiral, fate is determinate (fixed) radial, fate is indeterminate Blastopore becomes mouth becomes anus Coelom mesoderm arises from paired mesodermal cells near the pouches form from the blastopore, with primitive gut wall; splitting forming the they enlarge and fuse coelom to form the coelom Introduction to Chordates Crash Course to Chordates