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Unit 5 animal reproduction and development
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  • 1. UNIT 5:ANIMALREPRODUCTION ANDDEVELOPMENTCampbell & Reece, 2010:Chapters 46, 47
  • 2. INTRODUCTION Animal reproduction takesmany forms Animal form and function canbe viewed broadly asadaptations contributing toreproductive success. Both asexual and sexualreproduction occur in theanimal kingdom.
  • 3. Sexual reproductionIs the creation of an offspringby fusionof a male gamete (sperm)and female gamete (egg)to form a zygote
  • 4. Asexual reproductionIs creation of offspringwithout the fusion of egg andsperm.
  • 5. ASEXUALREPRODUCTION
  • 6. Mechanisms of AsexualReproductionMany invertebratesreproduce asexually.One of these is by theprocess of fission.FISSION: Is the separation ofa parent into two or moreindividuals of about thesame size.FISSION OF ANAMOEBA
  • 7. Fission of a sea anemone to producertwo daughter organisms
  • 8. Second method: BUDDINGIn budding, new individuals arisefrom outgrowths of existing onesBUDDING OF AHYDRA
  • 9. Third method: FRAGMENTATIONIs breaking of the body into pieces, some or all of which develop intoadults.Fragmentation must be accompaniedby regeneration - regrowth of lostbody partsFRAGMENTATION ANDREGENERATION OF SEA STARS
  • 10.  Fourth method: Parthenogenesis Is the development of a newindividual from an unfertilized egg
  • 11. SEXUALREPRODUCTION
  • 12. Introduction to sexualReproduction in animalsAlmost all eukaryotic speciesreproduce sexually.Sexual reproduction results ingenetic recombination –variation within species.
  • 13. Genetic recombination providespotential advantages:1. An increase in variation in offspring,2. An increase in the reproductivesuccess of parents in changingenvironments.3. An increase in the rate ofadaptation.4. Elimination of harmful genes froma population.
  • 14. REPRODUCTIVECYCLES ANDPATTERNS
  • 15. REPRODUCTION CYCLES ANDPATTERNSOvulation is the release of matureeggs at the midpoint of a female cycle.Most animals exhibit reproductivecycles related to changing seasons.Reproductive cycles are controlled byhormones and environmental cues
  • 16. Animals may reproduce asexually orsexually, or they may alternate thesemethods.Lizards reproduce only by a complex formof parthenogenesis that involves thedoubling of chromosomes aftermeiosisAsexual whiptail lizards are descendedfrom a sexual species, and females stillexhibit mating behaviours.
  • 17. Sexual behavior inparthenogenetic lizards
  • 18. Sexual reproduction is a specialproblem for organisms thatseldom encounter a mate.One solution is hermaphroditism,in which each individual has maleand female reproductive systemsSome hermaphrodites can self-fertilize.C. elegans makes both spermand eggs and can reproduceby self-fertilization.
  • 19. Individuals of some species undergosex reversalsSome species exhibit male tofemale reversal (for example,certain oysters),while others exhibit female to malereversal (for example, a coral reeffish)
  • 20. HOW DOORGANISMSENSURE THESURVIVAL OFTHEIROFFSPRING?
  • 21. Ensuring the Survival of OffspringAll species produce moreoffspring than the environmentcan handle.The proportion that survives issmall.Species with external fertilizationproduce more gametes thanspecies with internal fertilization.
  • 22. Species with internal fertilizationprovide greater protection of theembryos and more parental care.The embryos of some terrestrial animalsdevelop in amniote eggs withprotective layers.Other animals retain the embryo,which develops inside the female.In many animals, parental care helpsensure survival of offspring.
  • 23.  AMNIOTIC EGG OF A CHICKEN
  • 24.  PARENTAL CARE OF AN INVERTEBRATE
  • 25. GAMETEPRODUCTIONAND DELIVERY
  • 26. Gamete Production and DeliverySexually reproducing animals havesystems producing gametes.These individuals have gonads -organs producing gametes.Male gonads : TestisFemale gonads: OvariesSome gametes form fromundifferentiated tissue.
  • 27. GONADS: MALE – TESTIS ANDFEMALE - OVARIES
  • 28. Complex systems contain manysets of: accessory tubes and glands thatcarrynourish,and protect gametes anddeveloping embryos.
  • 29. Some organisms have a cloaca:is a common opening betweenthe external environment and thedigestive, excretory, andreproductive systemsCommon in non-mammalianvertebrates;Mammals usually have aseparate opening to the digestivetract.
  • 30. CLOACA OF A LIZARD
  • 31. Monogamy is relatively rareamong animals.Males and/or females whichhave mechanisms to decreasethe chance of their mate matingwith another individual.
  • 32. COURTSHIPBEHAVIOURCourtship, inanimals –behaviour thatresults in mating andeventualreproduction
  • 33. Courtship behaviours caninclude:special calls,postures, andmovements,special plumage,bright colours orother ornamentation
  • 34. EXAMPLESThe dancing done by malebirds of paradise.
  • 35. Method ofreproduction inwhich eggs arelaid andembryosdevelop
  • 36. Three Methods of reproduction inwhich eggs are laid and embryosdevelopOviparyOvoviviparyVivipary
  • 37. OVIPARYOUS ORGANISMSReproduction in which eggs are laidand embryos develop outside themothers body.Each egg eventually hatching into ayoung animal.Little or no development occurs withinthe mothers body.Most invertebrates and manyvertebrates reproduce in this way.
  • 38. Ovoviviparous:Animals produce eggs, but insteadof laying the eggs, the eggs developwithin the mothers body.The young eat unfertilized eggs inthe womb for nourishmentThe young are born alivewithout placental attachment(umbilical cord),as certain reptiles, fishes, sharks,insects.
  • 39. VIVIPAROUSWhere the embryo developswithin the uterus.and is nourished through ayolk sac placenta from themother’s blood.Young are born alive. most mammals and somereptiles and fishes.
  • 40. OVOVIVIPAROUS
  • 41. ANIMALDEVELOPMENT
  • 42. Introduction to animal developmentThe question of how a zygote becomesan animal?The first step is cell division (mitosis)Second step: Cell differentiation (Is thespecialization of cells in structure andfunction)Third step: Morphogenesis (Is theprocess by which an animal takesshape.)
  • 43. Fertilization
  • 44. FertilizationFertilization depends onmechanisms that bring togethersperm and eggs of the samespecies.All fertilization requires: critical timing,mediated by: environmental cues, pheromones, and/or courtship behaviour.
  • 45. FertilizationTwo types of fertilizations: External fertilization Internal fertilization
  • 46. External FertilizationIn external fertilization,eggs shed by the femaleare fertilized by sperm of malein the external environment.
  • 47. Internal FertilizationIn internal fertilization,sperm are deposited in or near thefemale reproductive tract,and fertilization occurs within thetract
  • 48. Internal FertilizationInternal fertilization requires: behavioural interactions and compatible copulatory organs.MALECOPULATORYORGANS
  • 49. PROCESS OF FERTILIZATIONFertilization brings the haploid nucleiof sperm and egg together, forming adiploid zygote.The sperm’s contact with the egg’ssurface initiates metabolic reactionsin the egg that trigger the onset ofembryonic development.Metabolic reactions:Acrosomal reactionCortical reaction
  • 50. ACROSOMAL REACTIONTriggered when the sperm meetsthe egg.The acrosome, at the tip of thesperm releases hydrolytic enzymesthat digest material surrounding theegg.Gamete contact depolarizes theegg cell membrane and sets up afast block to polyspermy.
  • 51. Sperm contacts egg
  • 52. Acrosome releaseshydrolytic enzymes –digest egg jelly coat
  • 53. Actin filaments of acrosomal processbinds to the sperm binding receptors.
  • 54. Plasma membranes of spermand egg fuses
  • 55. Sperm releases haploid nucleus in egg cytoplasm– fast block prevent polyspermy.
  • 56. The Cortical ReactionInitiated by the fusion of egg andsperm.It causes a rise in Ca2+.This stimulates cortical granules torelease their contents outside theegg.Cause formation of a fertilizationenvelope (functions as a slowblock to polyspermy.)
  • 57. Rise of calcium in egg andformation of fertilization envelope
  • 58. Activation of the EggThe sharp rise in Ca2+ in the egg’scytosol increases the rates ofcellular respiration and proteinsynthesis by the egg cell.Now the egg is said to be activated.The sperm nucleus merges with theegg nucleus to form a diploidzygote and cell division begins.
  • 59. EMBRYONIC DEVELOPMENT AFTERFERTILIZATION3 PROCESSES OCCURE IN AN EMBRYOAFTER FERTILIZATION:1.Cleavage2.Gastrulation3.Organogenesis
  • 60. 1. CLEAVAGEA period of rapid cell divisionwithout growth.This creates a hollow ball of cellscalled a blastula.The blastula consists of manysmaller cells called blastomeresThe hollow part of the blastula isfilled with fluid and called ablastocoel.
  • 61. CELL DIVISION OF A FERTILIZEDEGG FORMING A BLASTULA
  • 62. Two types of cleavageMeroblastic cleavage, incompletedivision of the egg, occurs in specieswith yolk-rich eggs, such as reptilesand birds.Holoblastic cleavage, completedivision of the egg, occurs in specieswhose eggs have little or moderateamounts of yolk, such as sea urchinsand frogs
  • 63. 2. GastrulationGastrulation –rearranges the cells of ablastula into a three-layeredembryo, called a gastrula,which has a primitive gut(archenteron)and opens in ablastopore.
  • 64. Three embryonic germ layersof the gastrulaThe ectoderm forms the outerlayerThe endoderm lines thedigestive tract.The mesoderm partly fills thespace between the endodermand ectoderm.
  • 65. GASTRULA OF A FROG
  • 66. 3. ORGANOGENESISDuring organogenesis, variousregions of the germ layersdevelop into organs.Early in vertebrateorganogenesis, the notochordforms from mesoderm, and theneural plate forms fromectoderm.
  • 67. ORGANOGENESISOF A FROG
  • 68. The neural plate soon curvesinward, forming the neural tubeThe neural tube will becomethe central nervous system(brain and spinal cord).
  • 69. THE FATE OF THE 3 GERMLAYERSFig. 47-14ECTODERM MESODERM ENDODERMEpidermis of skin and itsderivatives (including sweatglands, hair follicles)Epithelial lining of mouthand anusCornea and lens of eyeNervous systemSensory receptors inepidermisAdrenal medullaTooth enamelEpithelium of pineal andpituitary glandsNotochordSkeletal systemMuscular systemMuscular layer ofstomach and intestineExcretory systemCirculatory and lymphaticsystemsReproductive system(except germ cells)Dermis of skinLining of body cavityAdrenal cortexEpithelial lining ofdigestive tractEpithelial lining ofrespiratory systemLining of urethra, urinarybladder, and reproductivesystemLiverPancreasThymusThyroid and parathyroidglands
  • 70. AMNIOTES
  • 71. Developmental Adaptations ofAmniotesEmbryos of birds, other reptiles,and mammals develop in a fluid-filled sac in a shell or the uterusOrganisms with these adaptationsare called amniotes.
  • 72. During amniote development, fourextraembryonic membranes form aroundthe embryo:The chorion functions in gas exchangeThe amnion encloses the amniotic fluidThe yolk sac encloses the yolkThe allantois disposes of waste productsand contributes to gas exchange.
  • 73. EXTRAEMBRYONIC LAYERS OF BIRDS
  • 74. PRECOCIALAND ALTRICIALDEVELOPMENTPRECOCIAL YOUNGALTRICIAL YOUNG
  • 75. At birth the young may be well-developedand able to move about at once, this iscalled precocial development.If at birth the young are maybe blind,hairless, and essentially helpless, it iscalled altricial development.In general, precocial young are born aftera relatively long gestation period and in asmall litter.Hares and many large grazing mammalsbear precocial offspring.Rabbits, carnivores, and most rodentsbear altricial young.