Embryogenesis is the process by which the embryo is formed and develops. It starts with the fertilization of the ovum, which is then called a zygote. The zygote undergoes rapid mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of an embryo. It occurs in both animal and plant development, this article will adress the common features among different animals. Categories: Biology stubs | Developmental biology ... Categories: Biology stubs ... A human ovum An ovum (also oocyte, ovocyte, or loosely, egg or egg cell) is a female sex cell or gamete. ... A zygote (Greek: ζυγωτόν) is a cell that is the result of fertilization. ... Overview of the major events in mitosis In biology, mitosis is the process of chromosome segregation and nuclear division that follows replication of the genetic material in eukaryotic cells. ... Cell division is the process of a biological cell (called a mother cell) dividing into two daughter cells. ... In embryology, cleavage is the division of cells in the early embryo. ... Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a type. The morphology of a cell may change dramatically during differentiation, but the genetic material remains the same, with few exceptions. ... Plant embryogenesis is a sexual or asexual reproductive process that forms new plants. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria Acoelomorpha Orthonectida Rhombozoa ?Myxozoa Superphylum Deuterostomia    Chordata (vertebrates, etc. ...

The zygote

The egg cell (and hence the fertilized egg) is always asymmetric, having an "animal pole" (future ectoderm and mesoderm) and a "vegetal pole" (future endoderm), it is also covered with different protective envelopes. The first envelope, the one which is in contact with the membrane of the egg, is made of glycoproteins and is called vitelline membrane (zona pellucida in mammals). Different taxa show different cellular and acellular envelopes. The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. ... Mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... The endoderm is one of the three germ layers of the developing embryo, the other two being the ectoderm and the mesoderm. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that encapsulate the cell. ... A glycoprotein is a macromolecule composed of a protein and a carbohydrate (a sugar). ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... A taxon (plural taxa) is an element of a taxonomy, e. ...

Cleavage

The zygote undergoes rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic (total) or meroblastic (partial). The different cells derived from cleavage (up to the blastula stage) are called blastomeres. The cell cycle is the cycle of events in a eukaryotic cell from one cell division to the next. ... The egg yolk is the yellow inside an egg. ... In embryology, cleavage is the division of cells in the early embryo. ... A blastomere is the structure which results from the divisions of a fertilised egg during embryonic development . ...

In holoblastic eggs the first cleavage always ocurrs along the vegetal-animal axis of the egg, the second cleavage is perpendicular to the first. From here the spatial arrangement of blastomeres can follow various patterns, due to different planes of cleavage, in various organisms:

Slate pencil urchin (cidaroid) Group of black, long-spined Caribbean sea urchins, Diadema antillarum (Philippi) Sea urchin roe. ... Families Asymmetronidae Branchiostomidae The lancelets (subphylum Cephalochordata, and traditionally known as the amphioxus) are a group of primitive chordates. ... Classes Ascidiacea Thaliacea Appendicularia Urochordata (sometimes known as tunicata and commonly called urochordates, tunicates or sea squirts) is the subphylum of saclike filter feeders with input and output siphons. ... For other uses, see Amphibian (disambiguation). ... Classes and subclasses Class Polychaeta (paraphyletic?) Class Clitellata    Oligochaeta - Earthworms and others    Acanthobdellida    Branchiobdellida    Hirudinea - Leeches Class Myzostomida Class Archiannelida (polyphyletic) Class Echiura *Some authors consider the subclasses under Clitellata to be classes The annelids, collectively called Annelida, are a large phylum of animals, comprising the segmented worms, with about... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Atlantic herring, Clupea harengus, the most abundant fish species in the world. ... Orders Many - see section below. ... Orders  Crocodilia - Crocodilians scary crocodiles. ... Orders Subclass Apterygota Symphypleona - globular springtails Subclass Archaeognatha (jumping bristletails) Subclass Dicondylia Monura - extinct Thysanura (common bristletails) Subclass Pterygota Diaphanopteroidea - extinct Palaeodictyoptera - extinct Megasecoptera - extinct Archodonata - extinct Ephemeroptera (mayflies) Odonata (dragonflies and damselflies) Infraclass Neoptera Blattodea (cockroaches) Mantodea (mantids) Isoptera (termites) Zoraptera Grylloblattodea Dermaptera (earwigs) Plecoptera (stoneflies) Orthoptera (grasshoppers, crickets...

Blastula and Gastrula

Blastulation begins after the cleavage has produced 128 cells, in this stage the embryo is called a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel). A cell is a single unit or compartment, enclosed by a border or wall. ... Embryogenesis is the process of cell division and cellular differentiation which leads to the development of an embryo. ...

In mammals blastulation leads to the formation of the blastocyst, which must not be confused with the blastula, even though being similar in structure their cells have different fates. Embryogenesis is the process of cell division and cellular differentiation which leads to the development of an embryo. ...

During gastrulation cells migrate to the interior of the blastula, consecuently forming two (in diploblastic animals) or three (triploblastic) germ layers, the embryo during this process is called gastrula. Gastrulation is a dramatic restructuring of the animal embryo during the gastrula phase. ... Diploblastic is a condition of the ovum in which there are two primary germinal layers: the ectoderm and endoderm. ... Triploblastic is a condition of the ovum in which there are three primary germinal layers: the ectoderm, mesoderm, and endoderm. ... A germ layer is a layer of cells during fetal development that all have similar fates. ... The gastrula phase of embryonic development is seen in all animals except the sponges. ...

• Among the different animals, different combinations of the following processes occur to place the cells in the interior of the embryo:
  • Epiboly (spreading of a sheet of cells under the external sheet of cells).
  • Ingression (cells move with pseudopods)
  • Invagination
  • Delamination (the external cells divide, leaving the daughters cells in the cavity)
  • Polar proliferation

• Other mayor changes during gastrulation:
  • Heavy RNA transcription, up to this point the RNA used was the one stored in the unfertilized egg.
  • Cells start mayor differentiation processes, losing their pluripotentiality.

Pseudopods or pseudopodia (false feet) are temporary projections of eukaryotic cells. ... Invagination is one of the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism, with a differentiated endoderm, mesoderm, and ectoderm. ... In genetics, transcription is the first of the two-step protein biosynthesis process. ... Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ... Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a type. The morphology of a cell may change dramatically during differentiation, but the genetic material remains the same, with few exceptions. ... In cell biology, a pluripotent cell is one able to differentiate into many cell types. ...

Organogenesis

At some point after the different germ layers are defined, organogenesis begins. The first stage in vertebrates is called neurulation, where the neural plate folds forming the neural tube. Other common organs or structures which arise at the time include the heart and somites, but from now on embryogenesis follows no common pattern among the different taxa of the animal kingdom. Organogenesis is a stage of animal development where the ectoderm, endoderm, and mesoderm are formed. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... In the early development of vertebrates, neurulation is the process of the neural plate folding into the neural tube. ... The neural plate is thick and flat bundle of ectoderm which develops in the embryo into the nervous system. ... The neural tube is the embryonal structure that gives rise to the brain and spinal cord. ... The heart and lungs (from an older edition of Grays Anatomy) The heart (Latin cor) is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions. ... In the developing vertebrate embryo, somites are masses of mesoderm distributed along the two sides of the neural tube and that will eventually become dermis, skeletal muscle and vertebrae. ... A taxon (plural taxa) is an element of a taxonomy, e. ... The Tree of Life stands as a symbol of the park, its base carved with the images of 325 animals. ...

In most animals organogenesis along with morphogenesis will result in a larva. The hatching of the larva, which must then undergo metamorphosis, marks the end of embryonic development. Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ... A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ... Transformation, or changing shape, from the Greek prefix meta-, equivalent to the English prefix trans-, and morph, meaning form. ...

See also

• Mammalian embryogenesis
• Drosophila embryogenesis
• Plant embryogenesis
• Cdx2