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Chapter 42 Animal Development Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. two days six weeks three weeks five months (2 days): Courtesy of the film Building Babies © ICAM/Mona Lisa; (3 weeks): © Lennart Nilsson, A Child is Born, 1990 Delacorte Press, pg. 81; (6 weeks): © Claude Edelmann/Photo Researchers, Inc.; (5 months): © Derek Bromhall/OSF/Animals Animals/Earth Scenes 1 Early Developmental Stages Fertilization Embryonic Development Effect of Yolk Neurulation and the Nervous System Developmental Process Cellular Differentiation Homeotic Genes Human Embryonic and Fetal Development Embryonic Development Fetal Development 2 Fertilization requires that sperm and egg interact to form a zygote A human sperm cell has three parts: The head Contains a haploid nucleus covered by acrosome containing enzymes, allowing the sperm to penetrate the egg. A middle piece Contains ATP - producing mitochondria The tail A flagellum that allows the sperm to swim 3 An egg Surrounded by the zona pellucida. A few layers of adhering follicular cells, collectively called the corona radiata. These cells nourished the egg when it was in a follicle of the ovary. 4 Fertilization involves the following steps: ◦ Several sperm penetrate the corona radiata ◦ Several sperm attempt to penetrate zona pellucida ◦ One sperm enters the egg and their nuclei fuse 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. microvilli of oocyte plasma membrane 2. Acrosomal enzymes digest a portion of zona pellucida. tail 1. Sperm makes its way through the corona radiata. 3. Sperm binds to and fuses with oocyte plasma membrane. sperm 4. Sperm nucleus enters cytoplasm of oocyte. corona radiata plasma membrane nucleus 5. Cortical granules release enzymes; zona pellucida becomes fertilization membrane. middle piece head acrosome fertilization membrane cortical granule sperm pronucleus 6. Sperm and egg pronuclei are enclosed in a nuclear envelope. oocyte plasma membrane zona pellucida egg pronucleus © David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images 6 During first stages of development, an organism is called an embryo Following fertilization, zygote undergoes cleavage Morula forms blastula with a hollow blastocoel Germ layers differentiate Ectoderm Mesoderm Endoderm 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Zygote Cleavage is occurring. blastocoel Blastula blastocoel Gastrulation is occurring. archenteron mesoderm ectoderm endoderm blastopore Early gastrula ectoderm endoderm b. Late gastrula a: © William Jorgensen/Visuals Unlimited; (Frog, p. 781): © Photodisc/Getty Images; 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. archenteron ectoderm mesoderm endoderm cross section a. Lancelet late gastrula archenteron mesoderm ectoderm yolk plug endoderm longitudinal section b. Frog late gastrula archenteron primitive streak mesoderm ectoderm yolk endoderm cross section c. Chick late gastrula 9 Nervous system ◦ Develops from midline ectoderm located just above the notochord ◦ Thickening of neural plate is seen along dorsal surface of the embryo ◦ Neural folds develop on either side of neural groove ◦ Neural grove becomes the neural tube 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. presumptive notochord neural plate neural groove ectoderm coelom mesoderm gut gut endoderm notochord archenteron a. neural tube notochord0 coelom b. yolk c. d. b: Courtesy Kathryn Tosney 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. neural tube somite notochord gut coelom ectoderm mesoderm endoderm 12 Development requires: ◦ Growth ◦ Cellular Differentiation ◦ Morphogenesis Adult body cells are totipotent ◦ Each contains all the instructions needed by any other specialized cell in the body 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. animal pole Dorsal plane of first division gray crescent Anterior site of sperm fusion Posterior Ventral vegetal pole Dorsal Anterior Ventral a. Zygote of a frog is polar and has axes. Posterior b. Each cell receives a part of the gray crescent c. Only the cell on the left receives the gray crescent 14 The ability of one embryonic tissue to influence the development of another tissue Developmental path of cells is influenced by neighboring cells 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Host embryo has undergone gastrulation. presumptive ectoderm ectoderm presumptive mesoderm presumptive endoderm Presumptive nervous tissue is removed from a donor embryo. Host embryo undergoes neurulation. normal host neural plate tissue transplant After removal of host tissue, donor presumptive nervous tissue is transplanted to belly region of host embryo. Due to normal induction process, a host neural plate develops. But donated tissue is not induced to develop into a neural a. Host embryo has undergone gastrulation. Host embryo undergoes neurulation normal host neural plate induced neural plate Presumptive notochord tissue is removed from a donor embryo. Donor presumptive notochord tissue is transplanted to a host embryo. Host belly tissue (which was removed) is returned to the host. Host develops two neural plates—one induced by host notochord tissue, the second induced by transplanted notochord tissue. b. 16 Roundworm, Caenorhabditis elegans Fruit Fly, Drosophila melanogaster Mouse, Mus musculus Fate Maps ◦ Show the destiny of each cell as it arises 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. egg gonad (8–16 divisions) cuticle (8–11 divisions) gonad vulva (10–13 divisions) cuticle egg intestine (3–6 divisions) nervous system (6–8 divisions) vulva sperm intestine nervous system pharynx (9–11 divisions) pharynx 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Protein products of gap genes b. Protein products of pair-rule genes c. Protein products of segment-polarity genes (All): Courtesy Steve Paddock, Howard Hughes Medical Research Institute 19 Homeotic Genes control pattern formation ◦ Organization of differentiated cells into specific three-dimensional structures ◦ Certain genes control whether a particular segment will bear antennae, legs, or wings Homeotic genes all contain the same particular sequence of nucleotides, the homeobox ◦ Mice and humans have the same four clusters of homeotic genes ◦ They are located on four different chromosomes 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Hox-2 Hox-1 mouse chromosomes Hox-3 Hox-4 fly chromosome mouse embryo b. fruit fly embryo mouse fruit fly Courtesy E.B. Lewis 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. embryo allantois amnion yolk sac chorion Chick embryo chorion amnion allantois umbilical cord yolk sac fetal portion of placenta Human maternal portion of placenta 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Fertilization egg nucleus sperm nucleus secondary oocyte secondary oocyte zona pellucida corona radiata 5. Early blastocyst single cell = zygote 1. Ovulation fimbriae inner cell mass ovary oviduct 2-cell stage 6. Implantation 4-cell stage 3. Cleavage 8-cell stage early chorion 4. Morula (Fertilization): © Don W. Fawcett/Photo Researchers, Inc.; (2-cell): © Rawlins-CMSP/Getty Images; (Morula): © RBM Online/epa/Corbis; (Implantation): © Bettmann/Corbis 23 Human gestation time - time from conception to birth - approximately nine months Embryonic Development - Months 1-2 Fetal Development - Months 3-9 Extra-embryonic Membranes Chorion Amnion Allantois Yolk Sac 24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic cavity embryonic disk yolk sac blastocyst cavity trophoblast a. 14 days amniotic cavity embryo yolk sac chorionic villi chorion b. 18 days body stalk amniotic cavity embryo allantois yolk sac chorionic villi c. 21 days chorion amniotic cavity allantois yolk sac amnion chorionic villi d. 25 days amniotic cavity chorion digestive tract chorionic villi amnion umbilical cord e. 35+ days 25 First Week ◦ Morula transformed into blastocyst ◦ Gives rise to chorion Second Week ◦ Implanting begins ◦ Gastrulation occurs Inner cell mass flattened into embryonic disk Ectoderm and Endoderm differentiate 26 Third Week ◦ Nervous system and circulatory system appear Fourth and Fifth Weeks ◦ ◦ ◦ ◦ Umbilical cord is fully formed Limb buds appear Head enlarges Sense organs more apparent 27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. tail brain brain optic vesicle optic vesicle tail pharyngeal pouch pharyngeal pouch heart region of heart, liver liver limb bud limb bud umbilical vessel umbilical vessel a. somite b. gastrointestinal tract limb bud a: © Lennart Nilsson, A Child is Born, Dell Publishing 28 Sixth Through Eighth Weeks ◦ Head achieves normal relationship with the body ◦ Nervous system is developed enough to permit reflex actions 29 The placenta Begins formation once the embryo is fully implanted Provides exchange between maternal and embryonic circulations Gases Nutrients Wastes 30 Chorionic villi Project into the maternal tissues Surrounded by maternal blood sinuses; the maternal and fetal blood do not mix Exchange between the fetal and maternal blood takes place across the walls of the chorionic villi CO2 and wastes move across from the fetus O2 and nutrients flow from the maternal side By the tenth week, the placenta is fully formed 31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic fluid placenta umbilical cord endometrium vagina umbilical cord umbilical blood vessel chorionic villi maternal blood vessels Placenta 32 Fetal development (months 3–9) involves: Extreme increase in size The genitalia appear in the third month A fetus soon acquires hair, eyebrows, eyelashes, and nails A fetus at first only flexes its limbs and nods its head Later it moves its limbs vigorously A mother feels movements from the fourth month After 16 weeks, a fetal heartbeat is heard through a stethoscope. A fetus born at 24 weeks may survive 33 It is believed that at least 1 in 16 newborns has a birth defect Hereditary defects can sometimes be detected before birth Amniocentesis allows the fetus to be tested for abnormalities of development; Chorionic villi sampling allows the embryo to be tested; During preimplantation genetic diagnosis, eggs are screened prior to in vitro fertilization 34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic cavity amniotic fluid and fetal cells biochemical studies and chromosome analysis fetal cells centrifuge amniotic fluid cell culture culture medium fetal cells a. Amniocentesis ultrasound scanner suction tube biochemical studies and chromosome analysis Cells from chorionic villi b. Chorionic villi sampling laparoscope ovary uterus aspirator bladder large intestine c. Preimplantation genetic diagnosis chromosome and genetic analysis oocytes from ovaries 35 Have Good Health Habits Avoid Alcohol, Smoking, and Drugs of Abuse Avoid Certain Medications and Supplements Avoid Having X-rays ◦ Nutritious diet and avoid potentially harmful substances, radiation, and pathogens ◦ Alcohol consumption during pregnancy is a leading cause of birth defects ◦ Many preventable birth defects are caused by cigarette smoking ◦ Even prescription drugs may cause birth defects ◦ Penetrating forms of radiation such as X-rays can hinder cell division and damage DNA, ◦ A particular concern for the rapidly dividing and differentiating cells of a fetus. 36 When the fetal brain matures, the hypothalamus causes the pituitary to stimulate the adrenal cortex so that androgens are released. The placenta uses androgens as precursors for estrogens that stimulate the production of prostaglandin and oxytocin. The hormones estrogen, prostaglandin, and oxytocin all cause the uterus to contract and expel the fetus. The process of birth (parturition) has three stages: dilation of the cervix, birth of the baby, and expulsion of the placenta. 37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. placenta ruptured amniotic sac a. First stage of birth: cervix dilates b. Second stage of birth: baby emerges placenta uterus umbilical cord c. Baby has arrived d. Third stage of birth: expelling afterbirth © Karen Kasmauski/Corbis. 38 Early Developmental Stages Developmental Process Human Embryonic and Fetal Development Fertilization Embryonic Development Effect of Yolk Neurulation and the Nervous System Cellular Differentiation Homeotic Genes Embryonic Development Fetal Development 39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. two days six weeks three weeks five months (2 days): Courtesy of the film Building Babies © ICAM/Mona Lisa; (3 weeks): © Lennart Nilsson, A Child is Born, 1990 Delacorte Press, pg. 81; (6 weeks): © Claude Edelmann/Photo Researchers, Inc.; (5 months): © Derek Bromhall/OSF/Animals Animals/Earth Scenes 40