Animal Reproduction & Development

Acrosomal Process

Fertilization (Page 2) The signal transduction pathway causes large amounts Ca 2+ to be released into the cytoplasm of the egg Ca 2+ causes the cortical reaction  Ca 2+ causes changes in the granules of the egg (vitelline) membrane to become a hard fertilization envelope, so it resists the entry of other sperm  Sharp rise in Ca 2+ caused the egg to activate & develop ** HOWEVER, in parthenogenesis, the cortical reaction is triggered by electrical stimulation or Ca 2+ injection

Embryonic Development 3 Stages 1. Cleavage 2. Gastrulation 3. Organogenesis Cleavage – rapid mitotic division of the zygote  Immediately following fertilization  Early cellular divisions follow 1 of 2 patterns  Protosome or deuterosome

Protosome vs. Deuterosome Protosome Cleavage  Spiral & Determinant  Determinant – future of each cell is determined by the time it reaches the 4-cell stage  At the time of determination, if a cell is separated it will NOT develop into a complete embryo Deuterosome Cleavage  Radial & indeterminant  Indeterminant – each cell retains the capacity to develop into a complete & normal embryo

Cleavage Process -- Results in a fluid-filled ball called a blastula -- Blastomere – blastula cells -- Blastocoel – fluid-filled center

Gastrulation Def – process of rearrangement of the blastula Begins with formation of the blastophore (opening into the blastula) In protosomes, blastophore becomes mouth In deuterosomes, blastophore becomes anus Some of the cells at the surface of the embryo migrate into the blastophore = cavity called archenteron (primitive gut)

Gastrulation (Page 2) This cellular migration produces a 3-layered embryo  Called a gastrula Gastrula – consists of 3 differentiated cell layers  These 3 layers are collectively referred to as embryonic germ layers  They develop into all tissues of the adult Ectoderm – skin & nervous system Endoderm – viscera (lungs, liver, digestive organs, etc) Mesoderm – Muscle, blood, & bones

Gastrulation (Invertebrate)

Gastrulation (Vertebrate)

Embryonic Germ Layers

3 Questions What are the 3 stages of embryonic development? What are the 3 embryonic germ layers? What are the 3 differences between oogenesis & spermatogenesis?

Le Frog Embryo Fertilization – 1/3 of egg is yolk, and is limited to the lower half (called the vegetal pole)  Top half called animal pole and has a pigmented cap  Grey crescent appears on opposite side of sperm entry point Cleavage & Gastrulation  Yolk presence = uneven cleavage  Blastophore forms on the border of the gray crescent and the vegetal pole

Le Frog Embryo (Page 2) Involution – cells at the dorsal lip, but above the blastophore stream over the dorsal lip and into the blastophore These cells then become endoderm & mesoderm The ectoderm streaming inward is called Epibolic movement The blastocoel disappears and is replaced by another cavity called the archenteron The mesoderm opposite the blastophore = dorsal mesoderm

Le Frog Embryo (Page 3) Organogenesis – In chordates, forming first are:  Notochord (skeletal rod characteristic of all chordates)  Forms the dorsal mesoderm  Neural Tube (becomes CNS)  Forms the dorsal ectoderm  Formed by embryonic induction After the blueprints for the organs are established, embryo develops into a larval stage (tadpole) Metamorphosis takes the tadpole to frog

Le Bird Embryo Cleavage & Gastrulation – contains so much yolk that embryo develops on a flat disc (blastodisc) that sits on top of the yolk  Instead of grey streak, it is called primitive streak  Cells migrate over the primitive streak and flow inward to the archenteron  As cleavage & gastrulation occurs, the yolk gets smaller Extraembryonic Membranes – Tissue outside the embryo forms 4 extraembryonic membranes  These membranes support the growing embryo inside the shell

Le Bird Embryo (Page 2) The 4 embryonic membranes are: 1. Yolk Sac 2. Amnion 3. Chorion 4. Allantois 1. Yolk Sac – contains the yolk (food for embryo) 2. Amnion – encloses the embryo in protective amniotic fluid

Le Bird Embryo (Page 3) 3. Chorion – lies underneath the shell -- Allows for the diffusion of respiratory gases between the outside and the growing embryo 4. Allantois – like the placenta in mammals -- Conduit for respiratory gases between the environment and the embryo -- Stores uric acid from the embryo -- Uric acid is the nitrogenous waste from the embryo that accumulates until the chick hatches

Factors that influence Embryonic Development Cytoplasmic determinants – the importance of the cytoplasm surrounding the nucleus for embryonic development For example, if a sea-urchin embryo is cut to influence development:  If cut Longitudinally (some animal pole & vegetal pole cells), subsequent development is normal  If cut Horizontally (all animal pole or all vegetal pole cells), subsequent development is abnormal

8-Cell Stage BlastulaGastrula --If cut Longitudinally (some animal pole & vegetal pole cells), subsequent development is normal --If cut Horizontally (all animal pole or all vegetal pole cells), subsequent development is abnormal

Example of Cytoplasmic Determinants

The Grey Cresent Hans Spemann Embryonic development is affected by how their distribution is affected by the zygote’s characteristic pattern of cleavage Demonstrated that if the grey crescent was constricted to one side of the blastomere, then there was abnormal separation & development

Spemann’s Experiment

Embryonic Induction Def – the ability of one group of embryonic cells to influence the development of another group of embryonic cells Example:  Ordinarily dorsal ectoderm in gastrula  neural plate  If other ectoderm is transplanted in the same gastrula  neural plate (same as b4)  At late stage of development in gastrula, If transplant ectoderm  NO neural plate

Homeotic, Homeobox, or Hox Genes Def – master genes that control the expression of genes responsible for specific anatomical structures Play critical role in normal embryonic development

Example of Embryonic Induction -- Dorsal tube usually initiates a chain of inductions  neural tube development -- Speeman & Mangold -- Grafted dorsal lip onto ventral side of embryo -- The dorsal lip relocated induced the abdomen tissue to become neural tissue -- Termed primary organizer due to its crucial role in development

Videos eature=related eature=related NR=1 NR=1 =related =related