AP Biology Animal Reproduction & Development

AP Biology Oogenesis Meiosis 1 completed during egg maturation Meiosis 2 completed triggered by fertilization ovulation  Unequal meiotic divisions  unequal distribution of cytoplasm  1 egg  2 polar bodies What is the advantage of this development system? Put all your egg in one basket!

AP Biology Fertilization  fertilization  cleavage  gastrulation  neurulation  organogenesis

AP Biology Fertilization  Joining of sperm & egg  sperm head (nucleus) enters egg

AP Biology 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 Ca 2+  cortical granules fuse with z.p.  z.p. hardens to form fertilization envelope = slow block to polyspermy 5. Ca 2+ 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 Anterior Right Animal pole Gray crescent Dorsal Ventral Left Posterior Body axes Establishing the axes Future dorsal side of tadpole Point of sperm entry First cleavage Vegetal hemisphere Vegetal pole Point of sperm entry Animal hemisphere

AP Biology  Cleavage planes usually follow a pattern that is relative to the zygote’s animal and vegetal poles

AP Biology LE 47-9 Zygote 2-cell stage forming 8-cell stage 4-cell stage forming Animal pole Blasto- coel Blastula (cross section) Vegetal pole Blastula (at least 128 cells) 0.25 mm Eight-cell stage (viewed from the animal pole) 0.25 mm

AP Biology Cleavage  zygote  morula  blastula  establishes future development zygote blastula morula gastrulation

AP Biology  Establish 3 cell layers Establish 3 cell layers  ectoderm  outer body tissues  skin, nails, teeth  nerves, eyes, lining of mouth  mesoderm  middle tissues  blood & lymph, bone & notochord, muscle  excretory & reproductive systems  endoderm  inner lining  digestive system  lining of respiratory, excretory & reproductive systems Gastrulation ectoderm mesoderm endoderm protostome vs. deuterostome gastrulation in primitive chordates

AP Biology 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 (1,2 nd 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 Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderm, chordates) Eight-cell stage Spiral and determinate Radial and indeterminate Coelom Archenteron (a) Cleavage (b) Coelom formation Coelom Key Ectoderm Mesoderm Endoderm Mesoderm Blastopore Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. AnusMouth Digestive tube MouthAnus Mouth develops from blastopore.Anus develops from blastopore. (c) Fate of the blastopore

AP Biology Neurulation  Formation of notochord & neural tube  develop into nervous system Notochord Neural tube develops into vertebral column develops into CNS (brain & spinal cord)

AP Biology 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  all cells of mammalian embryos are totipotent until the 16-cell stage

AP Biology Organogenesis Umbilical blood vessels Chorion Amnion Yolk sac Allantois Fetal blood vessels Maternal blood vessels Bird embryo Mammalian embryo Placenta

AP Biology Placenta  Materials exchange across membranes

AP Biology Human fetal development 7 weeks4 weeks

AP Biology Human fetal development 10 weeks

AP Biology Human fetal development 12 weeks20 weeks

AP Biology Human fetal development  The fetus just spends much of the 2 nd & 3 rd 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 Birth positive feedback

AP Biology Intestine Placenta Umbilical cord Wall of uterus Vagina Cervix Birth (36 weeks) Bladder

AP Biology The end of the journey! And you think 9 months of AP Bio is hard !