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Animal Reproduction. 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. Animal Reproduction. Reproduction is asexual or sexual

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animal reproduction2
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
animal reproduction3
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
animal reproduction6
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
animal reproduction8
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)
animal reproduction9
Animal Reproduction
  • Reproduction is asexual or sexual
    • sexual reproduction
      • offspring differ genetically from parents
      • involves significant cost
      • resulting population exhibits genetic variability
animal reproduction10
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)
animal reproduction11
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
animal reproduction12
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
animal reproduction14
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
animal reproduction15
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
animal reproduction17
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
animal reproduction19
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
animal reproduction21
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
fertilization
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
fertilization24
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
mammalian barriers to sperm entry figure 43 5
mammalian barriers to sperm entryFigure 43.5

(follicle cells)

(glycoprotein)

fast block to polyspermy in sea urchin prevents entry by multiple sperm
fast block to polyspermy in sea urchin:prevents entry by multiple sperm

plasma membrane

electrical potential

rapid Na+ influx

slow block to polyspermy figure 43 6
slow block to polyspermyFigure 43.6

sperm entry

Ca2+ release

exocytosis

fertilization

envelope

fertilization28
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
animal reproduction30
Animal Reproduction
  • sexual identity in animals
    • many animals are dioecious
    • other animals are monoecious (hermaphroditic)
      • simultaneous hermaphrodites
      • sequential hermaphrodites
fertilization31
fertilization
  • fusion of sperm and egg
    • produces zygote
    • requires sperm & egg to be in close proximity
mating behavior
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
mating behavior35
mating behavior
  • internal fertilization
    • protects sperm from desiccation
      • spermatophores - sperm containers
        • released to environment
        • inserted into female genital opening
mating behavior36
mating behavior
  • internal fertilization
    • protects sperm from desiccation
      • copulation
        • direct transfer of sperm
        • requires accessory sex organs
          • penis
          • vagina or cloaca
development
development
  • site of development varies
    • oviparous
      • egg bearing
      • external development
    • viviparous
      • live bearing
      • internal development in uterus
    • ovoviviparous
      • development in eggs retained within body
human reproductive system
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
human reproductive system39
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
human reproductive system42
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
human reproductive system44
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

human reproductive system45
human reproductive system
  • hormonal control of sperm development
    • spermatogenesis is controlled by
      • follicle-stimulating hormone (FSH) &
      • testosterone
        • on Sertoli cells
slide46
control of male sex hormone productionFigure 43.10 [remember to study this figure and explanatory slides associated with it]
human reproductive system48
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
human reproductive system50
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
human reproductive system52
human reproductive system
  • female reproductive cycles
    • uterine cycle
      • growth of endometrium
        • ~days 5-19 of ovarian cycle
        • prepares for implantation
      • breakdown of endometrium
        • ~end of ovarian cycle
        • expelled from body through vagina
human reproductive system53
human reproductive system
  • hormonal control of reproductive cycles
    • GnRH
      • from hypothalamus
      • stimulates
    • gonadotropins (LH & FSH)
      • from anterior pituitary
      • stimulate
    • estrogen
      • from ovary
human reproductive system54
human reproductive system
  • hormonal control of reproductive cycles
    • ~ 5 days before start of ovarian cycle
      • anterior pituitary increases gonadotropins
      • follicle matures & increases estrogen
      • estrogen stimulates endometrial growth
      • estrogen feedback reverses to boost LH
      • LH causes release of secondary oocyte
human reproductive system55
human reproductive system
  • hormonal control of reproductive cycles
    • corpus luteum secretes estrogen & progesterone
      • maintain endometrial growth
      • inhibit gonadotropin release to
      • inhibit follicle development
    • without fertilization, corpus luteum degenerates
slide57
hormonal control of ovarian and uterine cyclesFigure 43.14 [remember to study this figure and explanatory slides associated with it]
human reproductive system58
human reproductive system
  • hormonal control of reproductive cycles
    • with fertilization
      • human chorionic gonadotropin (hCG)
        • is produced by embryo
        • sustains corpus luteum
      • gradually, embryo derived cells
        • produce estrogen & progesterone
        • prevent anterior pituitary from releasing gonadotropins