Animal Reproduction

1. Animal Reproduction

2. Animal Reproduction • Reproduction is asexual or sexual • asexual reproduction • offspring genetically identical to parent and siblings • saves costs of sexual reproduction • resulting population lacks genetic variability

3. Animal Reproduction • Reproduction is asexual or sexual • asexual reproduction • various methods • budding • outgrowth from body of parent • regeneration • regrowth of lost body parts or whole organisms

4. budding of hydraregeneration of a sea starFigure 43.1

5. parthenogenesis & viviparyin aphid

6. Animal Reproduction • Reproduction is asexual or sexual • asexual reproduction • various methods • parthenogenesis • production of offspring from unfertilized eggs • may require mating behavior to stimulate development

7. parthenogenesis in whiptail lizardsFigure 43.2

8. Animal Reproduction • Reproduction is asexual or sexual • sexual reproduction • offspring differ genetically from parents • involves significant cost • gametogenesis • mating (getting gametes together) • fertilization (syngamy - gamete fusion)

9. Animal Reproduction • Reproduction is asexual or sexual • sexual reproduction • offspring differ genetically from parents • involves significant cost • resulting population exhibits genetic variability

10. Animal Reproduction • Reproduction is asexual or sexual • sexual reproduction - genetic variability • combines genetic contributions from male and female parents • gamete genomes contain recombined chromosomes • crossing over (prophase I) • independent assortment (metaphase I)

11. Animal Reproduction • Reproduction is asexual or sexual • sexual reproduction • alternates the halving and doubling of genomes • meiosis reduces 2n genome to 1n • fertilization combines two 1n gametes

12. Animal Reproduction • meiosis is part of gametogenesis • gametogenesis occurs in the primary sex organs - the gonads • motile sperm are produced in testes • non-motile eggs (ova) are produced in ovaries

13. Early stagesof spermatogenesis and oogenesisFigure 43.3

14. Animal Reproduction • gametogenesis • germ cells enter the gonads during embryonic development • germ cells divide mitotically to produce spermatogonia or oogonia • spermatogonia and oogonia divide mitotically to produce primary spermatocytes and primary oocytes • meiosis produces spermatids and ootids

15. Animal Reproduction • spermatogenesis • meiosis I divides a primary spermatocyte • produces two secondary spermatocytes • haploid • connected due to incomplete cytokinesis • meiosis II divides secondary spermatocytes • produces four linked spermatids • spermatids develop into sperm

16. complete spermatogenesisFigure 43.3

17. Animal Reproduction • oogenesis • primary oocyte enters prophase I • arrests development at prophase I • remains in prophase I for some time • grows & accumulates nutrients, energy, RNA, ribosomes, organelles

18. human gametesdiffer in size

19. Animal Reproduction • oogenesis • primary oocyte resumes meiosis I • asymmetric division produces two cells • secondary oocyte • first polar body • secondary oocyte divides asymmetrically in meiosis II • ootid • second polar body

20. complete oogenesis, minus pausesFigure 43.3

21. Animal Reproduction • oogenesis • timing of meiosis and egg development varies • secondary oocyte pauses in development prior to meiosis II • meiosis II may occur after expulsion from the ovary • human ova completes meiosis II after fertilization

22. Fertilization • sperm/egg recognition • recognition molecules ensure that sperm interact with eggs of the same species • jelly layer activates acrosome • acrosomal enzymes digest jelly layer • acrosomal process bears bindinproteins • plasma membrane bears bindin receptors

23. sea urchin sperm/egg recognitionFigure 43.4

24. Fertilization • mammalian sperm/egg recognition • sperm capacitation occurs in female reproductive tract • superficial sperm enzymes digest cumulus • zona pellucida glycoproteins bind sperm head recognition proteins • acrosomal enzymes digest zona pellucida • plasma membrane proteins bind sperm adhesion proteins

25. mammalian barriers to sperm entryFigure 43.5 (follicle cells) (glycoprotein)

26. fast block to polyspermy in sea urchin:prevents entry by multiple sperm plasma membrane electrical potential rapid Na+ influx

27. slow block to polyspermyFigure 43.6 sperm entry Ca2+ release exocytosis fertilization envelope

28. Fertilization • egg activation • mammals • calcium release from ER • cortical granule fusion • removal of sperm-binding proteins • metabolic activation • increased cytoplasmic pH • increased O2 consumption • increased protein synthesis • nuclear fusion ~12 h after sperm entry

29. simultaneous hermaphroditic fertilization

30. Animal Reproduction • sexual identity in animals • many animals are dioecious • other animals are monoecious (hermaphroditic) • simultaneous hermaphrodites • sequential hermaphrodites

31. fertilization • fusion of sperm and egg • produces zygote • requires sperm & egg to be in close proximity

32. release of sperm and eggs

33. mating behavior • external fertilization • release of gametes into aquatic environment • chance meeting of egg & sperm • synchronized release by sessile animals • simultaneous release by motile animals

34. simultaneous release of sperm & eggs

35. mating behavior • internal fertilization • protects sperm from desiccation • spermatophores - sperm containers • released to environment • inserted into female genital opening

36. mating behavior • internal fertilization • protects sperm from desiccation • copulation • direct transfer of sperm • requires accessory sex organs • penis • vagina or cloaca

37. development • site of development varies • oviparous • egg bearing • external development • viviparous • live bearing • internal development in uterus • ovoviviparous • development in eggs retained within body

38. human reproductive system • male organs produce & deliver sperm • semen • sperm • produced in testes • stored in epididymis • transported through vas deferens • combined with fluids • ejaculated through urethra during copulation

39. human reproductive system • male organs produce & deliver sperm • semen • bulbourethral fluid • pH buffer & lubricant • seminal fluid • fructose, prostaglandins, mucus/protein • prostate fluid • modifies uterine environment • clots seminal fluid

40. male primary and accessory sex organsFigure 43.8

41. sperm production in seminiferous tubulesFigure 43.9

42. human reproductive system • sperm development • within the scrotum • within seminiferous tubules • developing sperm are engulfed by Sertoli cells • developing sperm migrate from periphery to lumen of tubule • mature sperm are released into lumen and travel to epididymis • Leydig cells produce testosterone

43. SpermatogenesisFigure 43.9

44. human reproductive system • hormonal control of sperm development • gonadotropin-releasing hormone (GnRH) • from hypothalamus, stimulates • luteinizing hormone (LH) • from anterior pituitary, stimulates -testosterone release from Leydig cells

45. human reproductive system • hormonal control of sperm development • spermatogenesis is controlled by • follicle-stimulating hormone (FSH) & • testosterone • on Sertoli cells

46. control of male sex hormone productionFigure 43.10 [remember to study this figure and explanatory slides associated with it]

47. oviduct cilia

48. human reproductive system • female sex organs • ovary produces eggs • eggs are released into oviduct • oviduct transports egg to uterus • embryo implants in uterine wall • cervix retains uterine contents during pregnancy; dilates during birth • sperm enter, baby departs through vagina

49. female primary and accessory sex organsFigure 43.11

50. human reproductive system • female reproductive cycles • ovarian cycle ~28 days • production of a secondary oocyte • surrounded, supplied by follicle cells • growth, maturation, first meiotic division • release from ovary • increased hormone production • follicle cells of corpus luteum • produces estrogen & progesterone