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LO Februrary 26th, 2019
Animal Development 1
Sections 53.1-53.3 (Define…
LO Februrary 26th, 2019
Animal Development 1
Sections 53.1-53.3
1. Describe the events necessary for fertilization to occur, including the effects of sperm on eggs. List the different ways that polyspermy is blocked.
Fertilization in Animals
- Sperm penetrates between granulose cells.
- Some of the zona pellucida is degraded by acrosomal enzymes.
- Sperm and egg plasma membranes fuse. ZP3
- The sperm nucleus dissociates and enters cytoplasm.
- Cortical enzymes harden zona pellucida.
- Other sperm are blocked.
- Sperm and egg nuclei are enclosed in a nuclear envelope.
Polyspermy:
- would result in a polyploid zygote with three or more sets of chromosomes.
- incompatible with animal development, although it is a mechanism of speciation in plants.
- alter the composition of the exterior egg coats, preventing any further sperm from penetrating through these layers.
- cortical granule enzymes remove critical sperm receptors from the outer coat of the egg.
- Fast Block: Change polarity of egg by using sodium, (sea urchins). (not humans)
- Slow Block: calcium will activate cortical granules to Harden the Zona Pellucida.
- Sea Urchins use both blocks because of external fertilization.
Effects of of Sperm Penetration
- the nucleus of the unfertilized egg is not yet haploid because it had not entered or completed meiosis prior to ovulation. Fusion of the sperm plasma membrane then triggers the eggs of these animals to complete meiosis. A single large egg with a haploid nucleus and one or more small polar bodies, which contain the other nuclei, are produced.
- triggers movements of the egg cytoplasm.
- increase in protein synthesis and metabolic activity.
- Define the terms cleavage and blastula, describing the two major patterns of cleavage and what is responsible for each of them. Distinguish between the cleavage patterns and blastula formation in frogs, birds, mammals, and Drosophila.
Bastula: the outermost blastomeres in the ball of cells produced during cleavage become joined to one another by tight junctions, belts of protein that encircle a cell and weld it to its neighbors. These tight junctions create a watertight seal that isolates the interior of the cell mass from the surrounding medium.
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- Define gastrulation, describing the germ layers that are formed and the mechanisms by which cells move during this process. Draw figures of gastrulation in sea urchins, frogs, birds, and mammals, comparing and contrasting the formation of the three germ layers and the effect of the amount of yolk.
Gastrulation
cell shape changes and cell movements, the cells of the blastula rearrange themselves to form the basic body plan of the embryo
Gastrulation in Frogs
- Define organogenesis, diagramming neurulation in a frog embryo.
diagramming neurulation
- Neurulation begins from the dorsal mesoderm from the notochord. Signaling molecules secreted by these mesodermal cells and other tissues cause the ectoderm to thicken and become the neural plate. The neural folds are the two ridges that form lateral edges of the neural plate.
- Formation of the neural plate is an example of induction.
- After the neural plate is formed, the cells changed shapes. This causing the the structure to curve inward. In curves in and then pinches off. Then, the neural plate can then roll itself into the neural tube.
- The neural tube will become the brains and the spinal cord. They are located by the sides of the notochord.
Organogenesis: the formation of organs.
During organogenesis, regions of the 3 embryonic germ layers develop into the rudiments of organs.
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Gastrulation in sea urchins.
- Echinoderms.
- Develop from relatively yolk-poor eggs and form hollow, symmetrical blastulas.
- Gastrulation begins when cells at the vegetal surface of the blastula change their shape to form a flattened vegetal plate
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Gastrulation in birds
- The avian blastula is made up of a disc of cells sitting atop the large yolk mass.
- Cells that migrate through the primitive streak into the interior of the embryo determines where gastrulation starts.
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Gastrulation in Animals
- A primitive streak forms the ectoderm layer, and cells destined to become mesoderm migrate into the interior.
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Germ Layers
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Basic Gastrulation.
1) Invagination-dents inward
2) Involution - forms new layer Endoderm
3) Ingression: Migration of cells to middle begins to form Mesoderm.
4) Delimitation - splits into two sheets completing
5) Epiboly; expansion of one cell layer over the other.
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The Effect of the Amount of Yolk.
- Less Yolk = Rapid Cleavage.
- More Yolk = Slow Cleavage
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- Describe the function of extraembryonic membranes and list the taxa that have them.
Functions
- Exchange Gases
- Transport Nutrients
- Eliminate Waste
Taxa
- HAVE: Amniotes (Birds, reptiles, mammals)
- NOT: Anamniotes (fish, amphibians)
Common Extraemnbryonic Membranes
- Amnion (thin ecotderm inner most membrane, produces amniotic fluid)
- Yolk Sac (endoderm, nutrition, primoridal germ cells(form gametes)/blood cells), shock absorber, prevents desiccation
- Allantois (endoderm, wastes gas exchange, mammals=fetal connected to mom interface)
- Chorion (Ectoderm, gas exchange, Mammals=respiration, nutrition, excrition, filtration, hormone synthesis)
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- Describe how cell movement and apoptosis are involved in animal development.
- Organogenesis begins when the neural plate forms from dorsal ectoderm to begin the process of neurulation.
- The neural plate next forms a neural groove and then a neural tube.
Apoptosis
Apoptosis is programmed cell death.
At various times in development, individuals cells, sets of cells or whole tissue are cease to develop, die and are engulfed by neighboring cells.
- An example would be the cells in the Fingers and toes when forming.
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- Describe the classic experiment of Spemann and Mangold, explaining the role of the organizer
The work of Spemman demostrated that the first two blatomeres of the frog embryo are totipotent, meaning that can each develop into all the different cell types of that species.
- The dorsal lip organizes the embryo's body plan.
- Describe how induction from the Spemann organizer influences the development of the dorsal-ventral axis of embryos.
- Biologist think that function/the cause of induction of the organizer is to inactivate BMP-4 (a protein) on the dorsal side of the embryo.
- The inactivation of BMP makes notochord and neural tube.
- Describe the tissues and organs that originate from each of the three embryonic germ layers.