animal reproduction. reproduction is asexual or sexual –asexual reproduction offspring genetically...
TRANSCRIPT
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Animal Reproduction
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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
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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
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budding of hydraregeneration of a sea star
Figure 43.1
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parthenogenesis &
viviparyin
aphid
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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
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parthenogenesis in whiptail lizardsFigure 43.2
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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)
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Animal Reproduction
• Reproduction is asexual or sexual
– sexual reproduction
• offspring differ genetically from parents
• involves significant cost
• resulting population exhibits genetic variability
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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)
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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
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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
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Early stages
of spermatogenesis
and oogenesis
Figure 43.3
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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
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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
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complete spermatogenesisFigure 43.3
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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
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human gametesdiffer
in size
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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
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complete oogenesis, minus pausesFigure 43.3
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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
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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 bindin proteins
• plasma membrane bears bindin receptors
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sea urchin sperm/egg recognitionFigure 43.4
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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
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(follicle cells)
(glycoprotein)
mammalian barriers to sperm entryFigure 43.5
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fast block to polyspermy in sea urchin: prevents entry by multiple sperm
plasma membrane electrical potential rapid Na+ influx
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sperm entry
Ca2+ release
exocytosis
fertilization envelope
slow block
to polyspermyFigure 43.6
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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
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simultaneous hermaphroditic fertilization
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Animal Reproduction• sexual identity in animals
– many animals are dioecious– other animals are monoecious
(hermaphroditic)• simultaneous hermaphrodites• sequential hermaphrodites
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fertilization• fusion of sperm and egg
– produces zygote– requires sperm & egg to be in close
proximity
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release of
sperm and eggs
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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
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simultaneous release of sperm & eggs
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mating behavior• internal fertilization
– protects sperm from desiccation• spermatophores - sperm containers
–released to environment–inserted into female genital opening
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mating behavior• internal fertilization
– protects sperm from desiccation• copulation
–direct transfer of sperm–requires accessory sex organs
»penis»vagina or cloaca
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development• site of development varies
–oviparous• egg bearing• external development
–viviparous• live bearing• internal development in uterus
–ovoviviparous• development in eggs retained within body
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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
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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
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male primary and accessory sex organsFigure 43.8
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sperm production in seminiferous tubules
Figure 43.9
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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
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SpermatogenesisFigure 43.9
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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
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human reproductive system• hormonal control of sperm development
– spermatogenesis is controlled by • follicle-stimulating hormone (FSH) &• testosterone
–on Sertoli cells
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control of
male sex hormone production
Figure 43.10 [remember to study this figure and
explanatory slides associated with it]
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oviduct cilia
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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
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female primary and accessory sex organs
Figure 43.11
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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
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stages of the ovarian cycleFigure 43.12
meiosis
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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
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human reproductive system• hormonal control of reproductive cycles
– GnRH • from hypothalamus• stimulates
– gonadotropins (LH & FSH)• from anterior pituitary• stimulate
– estrogen• from ovary
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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
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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
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Figure 43.13
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hormonal control of ovarian and
uterine cycles
Figure 43.14 [remember to study this figure
and explanatory slides associated with it]
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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