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Transcript
Animal Reproduction & Development AP Biology 2007-2008 Oogenesis What is the advantage of this development system? Unequal meiotic divisions unequal distribution of cytoplasm 1 egg 2 polar bodies Meiosis 1 completed during egg maturation ovulation Meiosis 2 completed triggered by fertilization AP Biology Put all your egg in one basket! Fertilization AP Biology fertilization cleavage gastrulation neurulation organogenesis Fertilization Joining of sperm & egg AP Biology sperm head (nucleus) enters egg Mammalian Fertilization 1. Sperm binds to receptors in zona pellucida (extracellular matrix of egg) 2. Acrosomal reaction: sperm releases hydrolytic enzymes to digest z.p. (Sea Urchins) Depolarization of membrane: prevent other sperm from binding = fast block to polyspermy 3. Sperm + Egg Fuse 4. Cortical reaction: sperm + egg fusion triggers release of Ca2+ cortical granules fuse with z.p. z.p. hardens to form fertilization envelope = slow block to polyspermy 5. Ca2+ release also triggers activation of the egg AP Biology Cleavage Repeated mitotic divisions of zygote 1st step to becoming multicellular unequal divisions establishes body plan different cells receive different portions of egg cytoplasm & therefore different regulatory signals AP Biology The eggs and zygotes of many animals, except mammals, have a definite polarity The polarity is defined by distribution of yolk, with the vegetal pole having the most yolk The development of body axes in frogs is influenced by the egg’s polarity AP Biology LE 47-8 Point of sperm entry Animal hemisphere Vegetal hemisphere Point of sperm entry Anterior Right Ventral Gray crescent Posterior AP Biology Vegetal pole Future dorsal side of tadpole First cleavage Dorsal Left Body axes Animal pole Establishing the axes Cleavage planes usually follow a pattern that is relative to the zygote’s animal and vegetal poles AP Biology LE 47-9 Zygote 0.25 mm 2-cell stage forming 4-cell stage forming Eight-cell stage (viewed from the animal pole) 8-cell stage 0.25 mm Animal pole Blastula (cross section) Blastocoel Vegetal pole Blastula (at least 128 cells) AP Biology Cleavage zygote morula blastula establishes future development zygote gastrulation AP Biology morula blastula Gastrulation gastrulation in primitive chordates Establish 3 cell layers ectoderm outer body tissues skin, nails, teeth nerves, eyes, lining of mouth mesoderm ectoderm middle tissues blood & lymph, bone & notochord, mesoderm muscle excretory & reproductive systems endoderm inner lining digestive system lining of respiratory, excretory & reproductive systems AP Biology protostome vs. deuterostome endoderm Testing… All of the following correctly describe the fate of the embryonic layers of a vertebrate EXCEPT A. neural tube and epidermis develop from ectoderm B. linings of digestive organs and lungs develop from endoderm C. notochord and kidneys develop from endoderm D. skeletal muscles and heart develop from mesoderm E. reproductive organs and blood vessels develop from mesoderm AP Biology Cleavage If spiral (diagonal cell division) and determinate = protostome development The develop fate of each cell is determined early on (1,2nd cell division) The blastopore becomes the mouth If radial (Up/down side/side cell division) and indeterminate = deuterostome development Cells in the early embryo can develop into a complete embryo The blastopore becomes the anus AP Biology Fig. 32-9 Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderm, chordates) Eight-cell stage Eight-cell stage Spiral and determinate (a) Cleavage Radial and indeterminate (b) Coelom formation Key Coelom Ectoderm Mesoderm Endoderm Archenteron Coelom Mesoderm Blastopore Blastopore Solid masses of mesoderm split and form coelom. Mesoderm Folds of archenteron form coelom. Anus Mouth (c) Fate of the blastopore Digestive tube Mouth Mouth develops from blastopore. AP Biology Anus Anus develops from blastopore. Neurulation Formation of notochord & neural tube develop into nervous system Neural tube Notochord develops into vertebral column AP Biology develops into CNS (brain & spinal cord) Patterns of development Cytoplasmic determinants: chemical signals such as mRNAs and transcription factors, influence pattern of cleavage Induction: interaction among cells that influences their fate, cause changes in gene expression Totipotent cells: capable of developing into all the different cell types AP Biology all cells of mammalian embryos are totipotent until the 16-cell stage Organogenesis Mammalian embryo Umbilical blood vessels Chorion Bird embryo Amnion Yolk sac Allantois Fetal blood vessels Placenta AP Biology Maternal blood vessels Placenta Materials exchange across membranes AP Biology Human fetal development 4 weeks AP Biology 7 weeks Human fetal development 10 weeks AP Biology Human fetal development 12 weeks AP Biology 20 weeks Human fetal development The fetus just spends much of the 2nd & 3rd trimesters just growing …and doing various flip-turns & kicks inside amniotic fluid Week 20 AP Biology Human fetal development 24 weeks (6 months; 2nd trimester) fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix AP Biology Human fetal development 30 weeks (7.5 months) umbilical cord AP Biology Getting crowded in there!! 32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming AP Biology positive feedback Birth AP Biology Birth (36 weeks) Intestine Placenta Umbilical cord Wall of uterus Bladder AP Cervix Vagina Biology The end of the journey! And you think 9 months of AP Bio is hard! AP Biology