Ch. 47 Animal Development - Ms. Emery's AP Biology

CH. 47 ANIMAL DEVELOPMENT Compiled by Micki Lewis And Stephanie Langga IN THE 18TH CENTURY Preformation Idea that an egg or sperm contains an embryo, or homunculus that grows as it develops.

Epigenesis Idea that the form of an animal gradually comes from an egg - proposed originally by Aristotle from watching a chick develop in its egg. *Displaced Preformation* MODERN TECHNOLOGY has enabled us to specify the stages of which human embryos develop. This one is at

about 6-8 weeks after conception. Cell Development - cytoplasmic determinants- proteins and RNA that also put together the genetic codes - differences emerge when uneven distribution appears ! ! ! A between early embryonic cells R EXT Cell Differentiation Model

- specialization of cells in structure and function Organisms d se u s e i c 1. Spe Morphogenesis a y d u t s to - when the organism takes shape and the cells go to their specific n

o i t s functional homes e u q - a - Repres ble to ent a larger CONCEPT 47.1 After fertilization, embryonic development

proceeds through cleavage, gastrulation, and organogenesis. FERTILIZATION Important processes regulating development, a developing stage in most animals occurs 1. Cleavage cell division creates a hollow ball of cells, the blastula 2. Gastrulation rearranges blastula into a three-layered zygote, the gastrula 3. Organogenesis interactions with three layers create FERTILIZATION

Main Function Combining haploid sets from 2 organisms into a single diploid cell (zygote) contact with sperm on the eggs surface activates metabolic processes for embryonic development Contact, Autosomal reaction, Fusion of sperm and egg membranes, Cortical reaction, and Studied SEA URCHINS!!! - Not vertebrates or chordates, but the characteristics are very similar.

~ Deuterostome Development Eggs are fertilized externally. FERTILIZATION IN SEA URCHINS Acrosomal Reaction reaction between the sperm tip (the acrosome) and egg The acrosome discharges hydrolytic enzymes Hydrolytic enzymes digest jelly coat Leads to the fusion of the sperm and egg plasma membranes

External Fertilization Cortical Reaction fusion causes a longerlasting polyspermy block Cortical granules fuse to the egg plasma membrane for initiation Fertilization envelope is formed from secretion of hardening enzymes This ensures that only one sperm enters

the egg cytoplas m. Activation of the Egg Egg Activation Rise of calcium ions increases rates of cellular respiration and protein synthesis OR, artificially activated by calcium ion injection (parthenogenesis) About 20 minutes later Creation of diploid nucleus Timing differs! Different species have different

times in meiosis and can stop in Mammal Fertilization Moist environment Sperm movement in female reproductive tract Zona Pellucida After going through follicle cells, the sperm reaches the cellular matrix of the egg (part sperm receptor) Binding induces acrosomal reaction Internal Afterwards Fertilizatio

polyspermy n NO fast block to Whole sperm is taken into 1. CLEAVAGE rapid cell division WITHOUT growth goes from the zygote into many smaller cells, or blastomeres Follows a specific pattern Fluid-filled cavity forms, blastoecoel, in the first five-seven divisions Fully forms into the blastula, a hollow ball of cells *Polarity of eggs and zygotes established as the egg develops. Defined by uneven distribution of cytoplasmic 1.5

CLEAVAG Holoblastic Cleavage E Yolk: stored nutrients - Key factor in influencing the pattern of cleavage - Often concentrated toward one pole: Division of the entire egg Vegetal pole Occurs in species with eggs that - Decreases significantly toward have moderate amounts of yolk EX. sea urchins, frogs, and mammals the animal pole, where polar bodies bud from the cell

Meroblastic Cleavage Incomplete division of the egg Occurs in species with yolk-rich eggs EX. birds and reptiles 2. GASTRULATIO Transforms blastula into a N gastrula Most animals have a dramatic rearrangement of cells. Cells near the blastula form three cell layers, or

germ layers : 1.Ectoderm The outer layer 2. Endoderm The lining of the embryonic digestive tract 3. Mesoderm Space between the ectoderm and endoderm 3. ORGANOGENES involves more localized shape IS changes in tissues and individual cells First

evidence of organ building: appearance of tissue folds, splits, and dense clustering of cells Notochord Skeletal rod characteristic of ALL chordate embryos Neural Tube The rolled neural plate, caused by cell shape change Neural Crest Cells (in vertebrates) Pinched off neural crest that migrates to parts of the embryo to form nerves, teeth, bone, etc. The fourth germ layer Somites Mesoderm lateral to the notochord that separate into blocks, AMNIOT ES Developmental Adaptations of Amniotes

embryos of birds, reptiles, and mammals Or amniotes Develop within a fluid-filled sac called the amnion in a shell or the uterus Also forms extraembryonic membranes 1.Chorion gas exchange 2.Amnion protective, fluidfilled cavity 3.Yolk Sac encloses yolk for nutrients 4.Allantois disposes waste products Mammalian Development Placental Mammals

Eggs are small and have few nutrients Holoblastic cleavage No polarity *similar pattern to birds and reptiles* Human early embryonic development goes through 4 stages MAMMALIAN DEVELOPMENT after fertilization and cleavage 1. Blastocyst (version of a blastula) implants in the uterus. Inner cell mass develops into the embryo and form the extraembryonic membranes

2. Trophoblast (outer epithelium of the blastocyst) supports the embryo but DOES NOT actually contribute to the embryo itself. (formation of the fetal position) 3. The embryo develops from the epiblast and hypoblast within the blastocyst. CONCEPT 47.2 Morphogenesis in animals involves specific changes in cell shape, position, and adhesion. MORPHOGENESIS major aspect of development in animals AND plants Only involves movement in cells of animals Can bring changes in shape or migration

Plants cannot move; rigid cell wall Changes in cell shape and cell position are in cleavage, gastrulation, and organogenesis. CELLULAR COMPONENTS & BEHAVIOR Cytoskeleton, Cell Motility, Role of Cell Adhesion Molecules and Convergent Extension Rearrangements change both the shape and position of the cells. Both occur in tissue invaginations Convergent Extension: a type of morphogenetic

movement where cells of a tissue rearrange themselves that it becomes narrower and and Extracellular Matrix 1. Cell Adhesion Molecules hold cells together in tissues Ex. Cadherins 2. Extracellular Matrix Fibers provide anchorage for cells Guides migrating cells to destinations CONCEPT 47.3

The developmental fate of cells depends on their history and on inductive signals. PRINCIPLES OF DIFFERENTIATION First Second During early cleavage divisions, embryonic cells must become different from one another. Once initial cell asymmetries are set up, subsequent interactions among the embryonic cells

influence their fate, usually by causing changes in gene expression. In many animals, the first differences result from uneven distribution of cytoplasmic determinants. (transcription factors like DNA binding proteins that activates one set of genes) Induction: mechanism that brings differentiation of the specialized cell types that make up an animal FATE MAPPING

-maps of embryos that show specific regions that develop into specific parts development in specific parts of OLDER embryos EX. lineage of C. elegans ESTABLISHING CELLULAR ASYMMETRIES In nonamniotes need unevenly distributes cytoplasmic determinants in the egg Establish body axes Difference between blastomeres from cleavage in the zygote Totipotent: - Differences matter! Undergo different fates with different cytoplasmic determinants -

In amniotes Local environmental differences Also establish initial differences of cells and body axes Development potential Capability of developing into all different cell types of a species As embryonic development proceeds, developmental potential of cells become limited INDUCTIVE SIGNALS Cell Fate Determination

Pattern Formation Cells in developing embryo receive and respond to positional information. Development of an animals spatial organization Dorsal Lip of blastopore in the gastrula functions as an organizer (or Spemanns organizer, gastrula organizer) Or AER (apical ectodermal ridge) and ZPA (zone of polarizing activity) of the vertebrate limb bud

Arrangement of organs and tissues in 3D space Inductions form the notochord, neural tube, and organs Control Pattern Formation Tells a cell where it is relative to the body axes Determines how the cell will respond to molecular signaling REFERENCES AP Biology book Bozeman Animal Development Video Crash course Animal Development

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