Chapter 46 - Animal Reproduction

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  • 1. Animal Reproduction Chapter 46
  • 2. How does the human reproductive system work?• Mammals, including humans produce gametes in paired organs called gonads• In males: testes (singular = testis); produce sperm• In females: ovaries; produce eggs
  • 3. Human male reproductive tractSee Fig. 46.10
  • 4. Human male reproductive tractTestes (inscrotum) Sperm Testosterone See Fig. 46.10
  • 5. Human male reproductive tractAccessorystructuresSeminal vesiclesProstate glandBulbourethral gland(together produce semen) See Fig. 46.10
  • 6. Human male reproductive tractAccessorystructures Epididymis(sperm storage) See Fig. 46.10
  • 7. Human male reproductive tractAccessorystructures Vas deferens(connects testes to urethra) See Fig. 46.10
  • 8. Testes produce sperm &testosteroneSperm production occursin seminiferoustubulesSee Fig. 46.12
  • 9. Testes produce sperm &testosteroneSperm production occursin seminiferoustubulesAt puberty, testosteroneproduction beginsin interstitial cellsSee Fig. 46.12
  • 10. Testes produce sperm &testosteroneSperm production occursin seminiferoustubulesSertoli cells regulatesperm production &nourish developingspermSee Fig. 46.12
  • 11. Testes produce sperm &testosteroneSperm production occursin seminiferoustubulesSpermatozoa areproduced byspermatogoniaSee Fig. 46.12
  • 12. SpermatogenesisSpermatogonia (2n) either undergo mitosis toproduce new spermatogonia, or undergo meiosis toproduce sperm (1n)See Fig. 46.12
  • 13. Human sperm – almost no cytoplasm; carries male DNA to egg DNAHead Nucleus – DNA Acrosome – Enzymes See Fig. 46.12
  • 14. Human sperm – almost no cytoplasm; carries male DNA to egg DNAHead Nucleus – DNA Acrosome – EnzymesMidpiece Mitochondria – Energy See Fig. 46.12
  • 15. Human sperm – almost no cytoplasm; carries male DNA to egg DNAHead Nucleus – DNA Acrosome – EnzymesMidpiece Mitochondria – EnergyTail Flagellum – Propeller See Fig. 46.12
  • 16. Human female reproductive tractSee Fig. 46.9
  • 17. Human female reproductive tract Fallopian tubes, Ovaries a.k.a. uterine tubes, Eggs a.k.a. oviducts Estrogen / progesterone Accessory structures receive & move sperm to egg & nourish ovary fimbriae uterus developing embryo Vagina – receives cervix sperm vagina Fallopian tubes – site of fertilization Uterus – site of development of embryo See Fig. 46.9
  • 18. Human female reproductive tract Fallopian tubes, Ovaries a.k.a. uterine tubes, Eggs a.k.a. oviducts Estrogen / progesterone Accessory structures receive & move sperm to egg & nourish ovary fimbriae uterus developing embryo Vagina – receives cervix sperm vagina Fallopian tubes – sites of fertilization Uterus – site of development of embryo See Fig. 46.9
  • 19. Oogenesis – formation of egg cells viameiosisIt has long been thought that women haveall their primary oocytes (halted atProphase of Meiosis I) bythe time they are born See Fig.46.11 & 46.13
  • 20. Monthly menstrual cycle coordinates:1) maturation of several eggs2) release of one egg3) preparation of the uterine lining forpossible pregnancy
  • 21. Hormonal control of the menstrual cycle:Hormones from the brain’s “master gland”(pituitary) initiate development of egg-bearingfollicles in the ovary
  • 22. Hormonal control of the menstrual cycle: Estrogen produced by egg-bearing folliclesstimulates the growth of the uterine lining
  • 23. Hormonal control of the menstrual cycle:Ovulation occurs on about day 14; remnants ofruptured follicle become the corpusluteum, which produces both estrogens andprogesterone
  • 24. Hormonal control of the menstrual cycle: Combination of estrogens + progesterone:1) Inhibits hormone release from pituitary,preventing development of more follicles2) Stimulates further growth of uterine lining
  • 25. Hormonal control of the menstrual cycle: If pregnancy does not begin:1) The corpus luteum breaks down2) Estrogens & progesterone levels fall3) Uterine lining is shed as menstrual flow
  • 26. Fertilization may lead to pregnancy…Sperm deposited in the vagina during copulation swim through the uterus into the Fallopian tubes, where they may encounter an egg Sperm Sperm Sperm Sperm Oocyte (egg)
  • 27. Fertilization may lead to pregnancy… Sperm release enzymes that break down the barriers around the egg (corona radiata and zona pelucida) oocyte Zona pellucida – Corona radiata – layer of jelly-like layeraccessory cells around egg around egg
  • 28. Fertilization may lead to pregnancy… Fusion of the nuclei of an egg and one sperm (fertilization) produces a zygote oocyte Zona pellucida – Corona radiata – layer of jelly-like layeraccessory cells around egg around egg
  • 29. If pregnancy begins, the embryo secretes ahormone that prevents the breakdown of the corpus luteum
  • 30. Corpus luteum continues to produce estrogensand progesterone, so the uterine lining continues to grow and develop
  • 31. Most pregnancy tests detect the presence of ahormone produced by the embryo – and present in the woman’s urine
  • 32. Fetal development… • The inner wall of the uterus together with embryonic tissues become the placenta, which transfers oxygen, carbon dioxide, nutrients and wastes between the mother and the developing fetus Maternal Maternal arteries veins Placenta Maternal portion Umbilical cord of placenta Fetal capillaries Fetal portion of Maternal blood placenta (chorion) pools Uterus Umbilical cordFigure 46.16
  • 33. Two basic reproductive modes• Asexual reproduction – Requires only one parent – Offspring are genetically identical to parent and to each other• Sexual reproduction – Requires meiotic cell division in two parents – Produces genetically variable offspring, with different combinations of parental genes
  • 34. Asexual reproduction: budding• Occurs in sponges and some cnidarians (e.g., Hydra)• Miniature animal begins as a bud on an adult, then becomes independent Budding in Hydra Adult Bud
  • 35. Asexual reproduction: fission followed by regeneration• Occurs in some cnidarians, flatworms and some segmented worms (annelids)• Body splits into two or more pieces• Each piece regenerates any missing body parts Fission in a sea anemone
  • 36. Asexual reproduction: fission followed by regeneration Grows new tail Anterior half with no tail Posterior Flatworm half with Growscinches in two no head new head
  • 37. Asexual reproduction: parthenogenesis• In rotifers, as well as some insects, fish, amphibians and reptiles the eggs produced by females develop directly into adults without being fertilized by sperm• This process is called parthenogenesis
  • 38. Aphid Baby aphid
  • 39. Whiptail lizard
  • 40. Queen bee(fertile female; diploid) Worker bee (sterile female; diploid) Drone (fertile male; haploid)
  • 41. Sexual reproduction requires fusion of sperm & egg
  • 42. Sexual reproduction in animals• Requires the production of gametes (egg and sperm), which are haploid (1n) cells• Gametes are produced from diploid (2n) cells by meiosis• Fusion of egg and sperm (fertilization) produces a diploid zygote, which divides by mitosis and develops into new diploid animal
  • 43. Some organisms arehermaphrodites; they produce botheggs and sperm & can self-fertilize E.g., tapeworm
  • 44. Some hermaphrodites cannot self- fertilize and so must exchangesperm to fertilize each other’s eggs E.g., some snails
  • 45. Most animals are dioecious, with separate females and males Female mallard Male mallard
  • 46. Most animals are dioecious, with separate females and males• Females produce large, non-motile eggs, that contain food reserves• Males produce small, motile sperm, with no food reserves
  • 47. External fertilization: Spawning• Union of sperm and egg takes place outside the bodies of the parents• External fertilization is common in animals that live in water• Release of sperm and eggs into the water is called spawning• Release is often synchronized using environmental cues (e.g., seasons, tides)
  • 48. Grunion spawning
  • 49. Coral spawning
  • 50. External fertilization: Amplexus• Male frogs mount females in a pose called amplexus• Female releases eggs and male then releases a cloud of sperm over them
  • 51. Internal fertilization• Important adaptation to life on land• Fertilization occurs inside female’s body• Copulation: Male deposits sperm directly into female’s reproductive tract
  • 52. Internal fertilization Damselflies mating