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Gametogenesis, Human gametes, Spermatogenesis, Oogenesis

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Gametogenesis Fertilization & Early Development Expert Education Endeavor in Science

The formation of sperm and ova requires meiosis:

Spermatogenesis Produces sperm in the male Oogenesis Produces ova in the female The formation of sperm and ova requires meiosis Gametogenesis Is the production of gametes Human gametes Are haploid cells that develop by meiosis

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Spermatogenesis Increases genetic variation Primary spermatocytes are produced throughout a male’s reproductive years Diploid cells undergo meiosis to form four haploid sperm

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Spermatogenesis

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Oogenesis Most of the process occurs within the ovaries Lifetime supply of primary oocytes is present at birth One primary oocyte matures each month to form a secondary oocyte If the secondary oocyte is fertilized, it completes meiosis and becomes a haploid ovum

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Oogenesis

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Interaction of sperm and egg The chemoattraction of the sperm to the egg by soluble molecules secreted by the egg The exocytosis of the acrosomal vesicle to release its enzymes The binding of the sperm to the extracellular envelope (vitelline layer or zona pellucida) of the egg The passing of the sperm through this extracellular envelop Fusion of egg and sperm cell plasma membranes

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Interaction of sperm and egg A chemotactic molecule, a 14-amino acid peptide called resact , has been isolated from the egg jelly of the sea urchin Arbacia punctulata A. punctulata sperm have receptors in their plasma membranes that bind resact and can swim up a concentration gradient of this compound until they reach the egg. The acrosomal reaction in sea urchins is initiated by contact of the sperm with the egg jelly . Contact with egg jelly causes the exocytosis of the sperm’s acrosomal vesicle and the release of proteolytic enzymes that can digest a path through the jelly coat to the egg surface .

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Interaction of sperm and egg The zona pellucida in mammals plays a role analogous to that of the vitelline envelope in invertebrates. This glycoprotein matrix, which is synthesized and secreted by the growing oocyte, plays two major roles during fertilization: it binds the sperm, and it initiates the acrosomal reaction A membrane molecule 83-kDa glycoprotein, ZP3 lays an important role in this interaction

Basic Concepts of Embryonic Development:

The key to development in all organisms is that each stage of development takes place in a highly organized fashion Basic Concepts of Embryonic Development

Early Stages of Development:

Early Stages of Development Fertilization Cleavage Gastrulation Neurulation

Fertilization:

Fertilization unequal gamete contributions egg contributes nutrients proteins, mRNAs mitochondria essential developmental genes (imprinted) sperm contributes centriole tubulin essential developmental genes (imprinted)

Fertilization:

Fertilization rearrangements of egg cytoplasm egg contents are distributed heterogeneously frog model system animal hemisphere contains nucleus heavily pigmented cortical cytoplasm lightly pigmented inner cytoplasm vegetal hemisphere contains nutrients unpigmented

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Fertilization results in the union of sperm and egg to form a zygote and triggers embryonic development

Cleavage - blastulation:

Cleavage - blastulation rapid cell divisions divisions oriented in specific directions little gene expression little cell growth packaging of cytoplasmic heterogeneity final product is a hollow ball of cells = blastula cells = blastomeres hollow cavity = blastocoel

Cleavage - blastulation:

Cleavage - blastulation yolky eggs alter pattern of divisions animal hemisphere divides normally vegetal (yolky) hemisphere divides less often produces larger cells

Mammalian Cleavage:

Mammalian Cleavage in oviduct slow cell divisions asynchronous cell divisions accompanied by gene expression produces a blastocyst inner cell mass - primordial embryo trophoblast - primordial placenta component

Gastrulation:

Gastrulation is the second major phase of embryonic development It adds more cells to the embryo It sorts all cells into three distinct cell layers The embryo is transformed from the blastula into the gastrula Gastrulation

Gastrulation-organizing the body plan:

Gastrulation-organizing the body plan undifferentiated cells produce germ layers ectoderm - prospective epidermis, nervous system endoderm - prospective gut tissues mesoderm - prospective organs, etc. germ layers migrate to new positions contact between layers allows inductive interactions to direct differentiation

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Formation of Endoderm The enlargement of the blastodermic vesicle is followed by the detachment of some cells from the inner cell mass. The detached cells are pushed into the blastocoel to form the embryonal endoderm or hypoblast. These cells rapidly increase in number to constitute the second complete layer inside the original outer layer of the blastodermic vesicle.

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Formation of Mesoderm After the completion of the endoderm as a cellular layer, cells from the caudal margin of the embryonic disc, start proliferating at an increased rate. This results in an increase in the thickening of the disc at that end. These cells then detach themselves and spread next to the endodermis to form the mesoderm. Formation of Ectoderm After the formation of the mesoderm the remaining cells of the embryonic disc arrange themselves outer to the mesoderm to form the ectoderm

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Types of cell movements during gastrulation Urchin Frog Urchin Fly, Mouse Frog 8.5

Organs start to form after gastrulation:

In the next stage of embryonic development, the cells of each germ layer begin to differentiate and specialize to form tissues, organs, and organ systems. In chordates the notochord develops from the mesoderm the neural tube develops from the ectoderm Organs start to form after gastrulation

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Universal mechanisms of animal development-similar basic structure

Neurulation:

Neurulation organogenesis formation of organs and organ systems caused by inductive interactions among germ layers vertebrate body segmentation alongside neural tube segments of mesoderm = somites somites direct development of vertebrae, ribs, trunk muscles, limbs, outgrowth of nerves, blood vessels, etc repeated segments are modified along the anterior/posterior axis Primary and Secondary neurulation

Changes in cell shape, cell migration, and programmed cell death give form to the developing animal:

Tissues and organs take shape in a developing embryo as a result of cell shape changes cell migration Changes in cell shape, cell migration, and programmed cell death give form to the developing animal

Pattern formation organizes the animal body:

Pattern formation is the emergence of a body form with structures in their correct relative positions It involves the response of genes to spatial variations of chemicals in the embryo Pattern formation organizes the animal body

The path of vertebrate development: An illustration of the major events in the development of Mus musculus, the house mouse. :

The path of vertebrate development: An illustration of the major events in the development of Mus musculus , the house mouse. ( a) Cleavage. ( b) Formation of blastula. ( c) Gastrulation . ( d) Neurulation . ( e) Cell migration. ( f) Organogenesis. ( g) Growth.

1]Cleavage:

1]Cleavage BLASTOMERES

2]BLASTULA FORMATION:

2]BLASTULA FORMATION MAMMALIAN BLASTOCYST

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ECTODERM ENDODERM

3] GASTRULATION:

3] GASTRULATION ECTODERM MESODERM ENDODERM

4] NEURULATION:

4] NEURULATION NEUTRAL PLATE

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NEURAL GROOVE NOTOCHORD

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NEURAL CREST NEURAL TUBE

5] cell migration:

5] cell migration MID GUT Mesoderm Spinal chord

6] organogenesis:

6] organogenesis intestine stomach MUSCLE SOMITES SPINAL CHORD BRAIN HEART

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