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Definitions topic 25.
- Cell division: cells, tissues and organs become specialized for a particular function.
- Morphogenesis: the development of the animal's shape, or body form and organization.
- Gametogenesis: the production of gametes.
- Fertilization: union of female and male gametes.
- Blastulation: production of a multicellular blastula.
- Gastrulation: formation of a 3 primary germ layers (ectoderm, endoderm and mesoderm).
- Neurulation: formation of the nervous system in chordates.
- Organogenesis: the development of organs from the 3 primary germ layers.
- Yolk: food reserves composed of protein and fat utilized by early embryo.
- Zygote: one diploid cell, fertilized egg.
- Blastula: multicellular hollow ball, or disc.
- Blastomeres: cells of blastula.
- Blastocoel: fluid filled cavity that forms within the blastula.
- Isolecithal egg: egg with small amount of evenly distributed yolk.
- Telolecithal egg: egg containing large amounts of yolk concentrated at one end.
- Blastodisc: nuclear-cytoplasmic region that is displaced toward the pole of egg where polar bodies developed from cell in meiosis.
- Animal Pole: half of egg with least amount of york (animal hemisphere).
- Vegetal pole: half of egg where yolk is concentrated (vegetal hemisphere).
- Holoblastic cleavage: cell divisions pass through entire fertilized egg. Only in isolecithal eggs. Blastocoel forms in the centre of blastula.
- Meroblastic cleavage: only active cytoplasm is divided. Only in telolecithal eggs. Blastocoel forms between two layers of cells within the blastoderm. Produces a cap of cells (blastoderm).
- Gastrula: an embryo made up of 3 embryonic layers; ectoderm, endoderm, mesoderm.
- Involution: surface cells migrate into the interior of the embryo.
- Archenteron: new cavity formed by involuted cells lined by endoderm.
- Endoderm: inside embryonic layer that forms digestive tract.
- Blastopore: opening of gastrula (deuterosomes = anus, protostomes = mouth).
- Ectoderm: outside layer of embryo.
- Mesoderm: layer in between ectoderm and endoderm.
- Neurulation: formation of dorsal, hollow neural tube. Only in chordates. Anterior end = brain, posterior end = spinal cord.
- Neural plate: ectodermal flattened cells extending from dorsal edge of blastopore to the anterior.
- Neural groove: formation from when the center of neural plate sinks.
- Neural folds: elevated folds from the plate.
- Neural tube: hollow tube formed when neural folds fuse together.
- Organogenesis: formation of rudimentary organs and organ systems.
- Ectoderm= skin, nervous system.
- Mesoderm= muscles, skeleton, gonads, excretory and circulatory syst.
- Endoderm= lining of digestive tract and associated organs.
- Fertilization envelope: halo that prevents multiple fertilizations (polyspermy).
- Pronuclei: the egg and sperm nuclei after they fuse.
- Vitelline layer: thin external layer in egg that contains species-specific sperm receptors.
Stages of Early development
- 1. Zygote.
- 2. Cleavage.
- 3. Blastula.
- 4. Involution.
- 5. Gastrula.
- 6. Neurulation.
- 7. Organogenesis.
Experiments Results: Sea Urchin, Sea star and Frog.
- Sea urchin and Sea star have holoblastic cleavage. As the number of cells increases, the size of cells decreases.
- The jelly coat of an echinoderm egg slowly dissolves in water and releases molecules that allow spem to penetrate and fertilization begins.
- Sea star and urchin have equal size of cells because yolk is evently distributed and have isolecithal eggs.
- Amphibians have moderately telolecithal eggs and holoblastic cleavage.
- A yolk plug forms in the blastopore.
- Neurulation forms a dorsal hollow nerve cord.
- They have unequal size of cells, the ones containing more yolk are larger.
Experiment Results: Chicken
- Oocytes: immature eggs.
- Ovulation: the release of oocytes into a single oviduct.
- Blastodisc: or geminal disc floats on a huge amount of yolk surrounded by plasma membrane.
- Fertilization happens if spem is present in the oviduct at ovulation and as it passes down other membranes are deposited on its surface.
- In unincubated egg: Egg albumin (watery, proteinaceous and white part of egg), Chalaza (whitish strands of albumin on yolk that forms as the egg passes down the oviduct), Cytoplasmic island (a small whitish disc lying on top of the yolk).
- At 16 hours of incubation: Gastrula stage; primitive streak is visible.
- At 24 hours of incubation: Neurulation; developing brain, neural folds, neural groove, spinal cord region and primitive streak are visible.
- At 48-96 hours of incubation: Organogenesis; developing brain, eye and ear, heart (atrium and ventricle), vitelline blood vessels (vessels that emerge from embryo and carry food from yolk to embryo), somites (will develop into musculature and other mesodermal organs), spinal cord are visible.
- At 96 hours: organs are bigger, anterior limb buds (wings) and posterior limb buds (legs) are visible.
- Also visible extraembryonic membranes:
- 1. Allantois (brings O2,carry CO2 away and store liquid wastes);
- 2. Amnion (thin membrane that encloses embryo in a fluid-filled sac);
- 3. Yolk sac;
- 4. Chorion.
- Chicken is strongly telolecithal and undergoes meroblastic cleavage.
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