Animal Development

1. Animal Development Lab 7

2. Animal Development Development takes place from the time that an organism is conceived to the time that it dies. Includes the development of the embryo, the emergence of larvae or juvenile stages, growth and maturation to sexual maturity, and the process of aging.

3. Biological Processes in Development A range of biological process are involved in development… Cell Division: results in more cells Cell Differentiation: results in specialization of cells for a particular function Morphogenesis: the development of the animal’s shape, body form, and organization

4. Developmental Terms to Know Cleavage: The series of mitotic cell divisions that produces a blastula from a fertilized ovum. Blastula: An early embryonic form produced by cleavage of a fertilized ovum and consisting of a spherical layer of cells surrounding a fluid-filled cavity. Gastrulation: The formation of the three primary germ layers; ectoderm, mesoderm, endoderm. Neurulation: The formation of the nervous system. (in chordates) Organogenesis: The development of organs from the primary germ layers.

5. Overview of the stages of early development • Stage 1: Preparation of the Egg, Fertilization, and Cleavage • Sperm and egg join to form one diploid cell, the zygote. • Many mitotic cell divisions produce a sphere of cells, the blastula. • The cells of the blastula are called blastomeres, while the hollow area in the middle of the blastula is the blastocoel. • Cleavage type is based upon amount and distribution of the yolk.

6. Overview of the stages of early development • Stage 2: Gastrulation • Transformation of the blastula into a gastrula. • Three germ layers form, the endoderm, the ectoderm, and mesoderm. • Surface cells migrate into the interior of the embryo (involution). • A new internal cavity is formed by this action (the archentron) and it is lined by the endoderm....which ultimately forms the digestive tract. • The archentreron opens to the outside through the blastopore, which becomes the anus in deuterostomes and the mouth in protostomes. • The surface cells form the ectoderm and the cells between the ectoderm and the endoderm are know as the mesoderm

8. Overview of the stages of early development • Stage 3: Neurulation • Only in Chordates • Ectodermal cells flatten to create an elongated neural plate. • The center of the plate sinks to become the neural groove ultimately creating a hollow neural tube. • Anterior end becomes the brain, posterior the spinal cord.

9. Overview of the stages of early development • Stage 4: Organogenesis • The formations of organs and organ systems. • Ectoderm forms skin and associated glands. • Mesoderm forms muscles, skeleton, excretory and circulatory systems. • Endoderm forms linings of the digestive tract and associated organs.

10. Extension of Development Development continues well past embryogenesis Development from zygote to adult: Ontogenesis Many organisms go through multiple life stages prior to adulthood Ex: Butterflies and other insects, Frogs and other amphibians.

11. Today’s Exercises Complete Exercise 2 (Development of an Amphibian) based on the video and slides available. Complete pages 186-188. Perform Lab Study B (Development of a Sea Star) pages 182-186. Observe the chick embryo under the microscope. Perform a smear of the Drosophila substrate and identify life stages. Sketch each one that you identify in your notebook.

12. Development of a Xenopus embryo http://www.youtube.com/watch?v=_Nl68Nc_Dlc&feature=related See pg 188 Fig. 6

13. The Fruit Fly • The Drosophila life cycle consists of a number of • stages: embryogenesis, three larval stages, a pupal stage, and the adult stage. • Obtain a slide and smear some of the substrate from the Drosophila colony onto it. • Look at it under the microscope and identify each of the life stages to the right