Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Animal Development
Document related concepts
Transcript
Developmental Stages in an Amphibian LE 21-4 Animal development Cell movement Zygote (fertilized egg) Eight cells Gut Blastula Gastrula Adult animal (cross section) (cross section) (sea star) Cell division Morphogenesis Observable cell differentiation Seed leaves Plant development Zygote (fertilized egg) Two cells Shoot apical meristem Root apical meristem Embryo inside seed Plant Most animals proceed through these stages during embryonic development: 1. Zygote 2. Early cleavage stages • Morula (solid ball) • Blastula (hollow ball) 3. Gastrula LE 47-7 Fertilized egg Four-cell stage Morula Blastula Starfish development, unfertilized egg. 16 blastomeres. 2 blastomeres. 32 blastomeres. morula 4 blastomeres. Starfish development, nonmotile blastula. LE 21-11a Unfertilized egg cell Sperm Molecules of another cytoplasmic determinant Molecules of a Nucleus cytoplasmic •Egg provides Fertilization proteins and determinant mRNAs required for early development Zygote (fertilized egg) Two-celled embryo •Cleavage asymmetrically Mitotic cell division divides cytoplasmic components; immediately establishing polarity Cytoplasmic determinants in the egg LE 47-8 Point of sperm entry Animal hemisphere Vegetal hemisphere Point of sperm entry Anterior Right Ventral Gray crescent Vegetal pole Future dorsal side of tadpole First cleavage Dorsal Left Posterior Body axes Animal pole Establishing the axes LE 47-9 Zygote 0.25 mm 2-cell stage forming 4-cell stage forming Eight-cell stage (viewed from the animal pole) 8-cell stage 0.25 mm Animal pole Blastula (cross section) Blastocoel Vegetal pole Blastula (at least 128 cells) Cleavage in 3 different animal lineages Gastrulation - Establishing Germ Layers (tissue development) • Ectoderm gives rise to outer covering and nervous system • Endoderm gives rise to the digestive tract • Mesoderm gives rise to muscle tissue Starfish development, gastrula during invagination. Starfish, late bipinnaria. Starfish development, mid-gastrula. LM X75. Starfish, young adult. Neurulation • The nervous system is the first organ system to develop – Notochord from mesoderm --> replaced with backbone – Neural tube from ectoderm --> spinal chord • Establishes basic body plan and layout of body parts Fig. 52.11 LE 47-14c Somites Eye SEM Neural tube Notochord Coelom Archenteron (digestive cavity) Somites Tail bud 1 mm Neural crest Somite LE 47-15 Eye Neural tube Notochord Forebrain Somite Heart Coelom Archenteron Endoderm Mesoderm Lateral fold Blood vessels Ectoderm Somites Yolk stalk YOLK Yolk sac Form extraembryonic membranes Early organogenesis Neural tube Late organogenesis Organogenesis Organogenesis is the formation of the organs. The layers are germ layers; they have specific fates in the developing embryo. • Organogenesis is the formation of the organs – Endoderm • The innermost layer • Goes on to form the gut – Mesoderm • In the middle • Goes on to form the muscles, circulatory system, blood and many different organs – Ectoderm • The outermost • Goes on to form the skin and nervous system Organogenesis Mammalian Development Human Prenatal Development • Gestation lasts 266 days from fertilization to birth • Development begins in the oviduct – About 24 hours after fertilization, the zygote has divided to form a 2-celled embryo – The embryo passes down the oviduct by cilia and peristalsis – The zona pellucida (a vestige of the egg shell) has dissolved by the 5th day, when the embryo enters the uterus – The embryo floats free for several days, nourished by fluids from glands in the uterine wall • At this point, it is called a blastocyst (same as blastula) 24 hrs 1 day 5 days 7 days • The trophoblast is the outermost layer of cells in the blastocyst • The trophoblast forms the chorion and amnion • The inner cell mass forms the embryo itself Development of the Placenta 12-day Human Embryo Organ Development • Begins during the first trimester – Gastrulation occurs during the 2nd and 3rd weeks, followed by neurulation (formation of the neural tube) – The heart beats spontaneously after 3.5 weeks – After the first two months of development, the products of conception are called a fetus Week 5 • At the end of the first trimester (first 3 months of development) – Fetus can be recognized as a human – ~56 mm long, and ~14 g – The sexes can be differentiated – Ears, eyes becoming welldeveloped, – Skeleton starting to develop – Notochord replaced with the developing vertebral column – Moves, ‘breathes’, makes sucking motions with thumb 33-day embryo measuring 7 x 3.2mm. Human embryo at 40 days. LE 21-12 Follicle cell Egg cell developing within Nucleus ovarian follicle Egg cell Nurse cell Fertilization Laying of egg Fertilized egg Egg shell Nucleus Embryo Multinucleate single cell Early blastoderm Plasma membrane formation Yolk Late blastoderm Body segments Cells of embryo Segmented embryo 0.1 mm Hatching Larval stages (3) Pupa Metamorphosis Adult fly Head Thorax Abdomen 0.5 mm Dorsal BODY AXES Anterior Posterior Ventral LE 21-14a Tail Head Wild-type larva Tail Tail Mutant larva (bicoid) Drosophila larvae with wild-type and bicoid mutant phenotypes LE 21-14b Nurse cells Egg cell Developing egg cell bicoid mRNA Bicoid mRNA in mature unfertilized egg Fertilization Translation of bicoid mRNA 100 m m Bicoid protein in early embryo Anterior end Gradients of bicoid mRNA and Bicoid protein in normal egg and early embryo LE 21-23 Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse LE 21-13 Eye Leg Antenna Wild type Mutant LE 21-24 Thorax Thorax Genital segments Abdomen Abdomen
