Chapter 46
Transcript of Chapter 46
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Chapter 46
Animal Reproduction
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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
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Human male reproductive tract
See Fig. 46.10
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Human male reproductive tract
Testes (in scrotum) Sperm Testosterone
See Fig. 46.10
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Human male reproductive tract
Accessory structures Seminal vesicles Prostate gland Bulbourethral gland
(together produce semen)
See Fig. 46.10
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Human male reproductive tract
Accessory structures Epididymis (sperm storage)
See Fig. 46.10
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Accessory structures Vas deferens
(connects testes to urethra)
Human male reproductive tract
See Fig. 46.10
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Testes produce sperm & testosterone
Sperm production occurs
in seminiferous
tubules
See Fig. 46.12
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Testes produce sperm & testosterone
Sperm production occurs
in seminiferous
tubules
At puberty, testosterone
production begins
in interstitial cells
See Fig. 46.12
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Testes produce sperm & testosterone
Sperm production occurs
in seminiferous
tubules
Sertoli cells regulate
sperm production &
nourish developing
sperm
See Fig. 46.12
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Testes produce sperm & testosterone
Sperm production occurs
in seminiferous
tubules
Spermatozoa are
produced by
spermatogonia
See Fig. 46.12
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Spermatogenesis
Spermatogonia (2n) either undergo mitosis to produce new spermatogonia, or undergo meiosis to produce sperm (1n)
See Fig. 46.12
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Human sperm – almost no cytoplasm; carries male DNA to egg DNA
HeadNucleus – DNAAcrosome –
Enzymes
See Fig. 46.12
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Human sperm – almost no cytoplasm; carries male DNA to egg DNA
HeadNucleus – DNAAcrosome –
Enzymes
MidpieceMitochondria –
Energy
See Fig. 46.12
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Human sperm – almost no cytoplasm; carries male DNA to egg DNA
HeadNucleus – DNAAcrosome –
Enzymes
MidpieceMitochondria –
Energy
Tail Flagellum –
Propeller
See Fig. 46.12
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Human female reproductive tract
See Fig.
46.9
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Ovaries Eggs Estrogen / progesterone
Accessory structuresreceive & move sperm to egg & nourish developing embryo Vagina – receives sperm Fallopian tubes – site of fertilization Uterus – site of development of embryo
fimbriae
cervix
Fallopian tubes,
a.k.a. uterine tubes,
a.k.a. oviducts
ovaryuterus
vagina
Human female reproductive tract
See Fig.
46.9
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Ovaries Eggs Estrogen / progesterone
Accessory structuresreceive & move sperm to egg & nourish developing embryo Vagina – receives sperm Fallopian tubes – sites of fertilization Uterus – site of development of embryo
fimbriae
cervix
Fallopian tubes,
a.k.a. uterine tubes,
a.k.a. oviducts
ovaryuterus
vagina
Human female reproductive tract
See Fig.
46.9
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Oogenesis – formation of egg cells via meiosisIt has long been thought that women have
all their primary oocytes (halted at
Prophase of Meiosis I) by
the time they are born
See Fig.
46.11 & 46.13
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Monthly menstrual cycle coordinates:
1) maturation of several eggs2) release of one egg3) preparation of the uterine lining for possible pregnancy
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Hormonal control of the menstrual cycle:Hormones from the brain’s “master gland” (pituitary) initiate development of egg-bearing follicles in the ovary
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Hormonal control of the menstrual cycle: Estrogen produced by egg-bearing follicles stimulates the growth of the uterine lining
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Hormonal control of the menstrual cycle:Ovulation occurs on about day 14; remnants of ruptured follicle become the corpus luteum, which produces both estrogens and progesterone
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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
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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
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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
Oocyte (egg)
SpermSperm
Sperm
Sperm
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Fertilization may lead to pregnancy… Sperm release enzymes that break down the barriers around the egg (corona radiata and
zona pelucida)
Corona radiata – layer of accessory cells around egg
Zona pellucida – jelly-like layer
around egg
oocyte
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Fertilization may lead to pregnancy… Fusion of the nuclei of an egg and one sperm
(fertilization) produces a zygote
Corona radiata – layer of accessory cells around egg
Zona pellucida – jelly-like layer
around egg
oocyte
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If pregnancy begins, the embryo secretes a hormone that prevents the breakdown of the
corpus luteum
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Corpus luteum continues to produce estrogens and progesterone, so the uterine lining continues
to grow and develop
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Most pregnancy tests detect the presence of a hormone produced by the embryo – and present
in the woman’s urine
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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
Umbilical cord
Fetalcapillaries
Maternal bloodpools
Umbilical cord
Maternal portionof placenta
Fetal portion ofplacenta (chorion)
Maternalarteries
Maternalveins
Figure 46.16
Placenta
Uterus
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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
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Asexual reproduction: budding
Adult
Bud
• Occurs in sponges and some cnidarians (e.g., Hydra)
• Miniature animal begins as a bud on an adult, then becomes independent
Budding in Hydra
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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 asea anemone
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Flatworm cinches in
two
Posterior half with no head
Grows new head
Anterior half with no tail
Grows new tail
Asexual reproduction:fission followed by regeneration
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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
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Aphid
Babyaphid
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Whiptail lizard
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Queen bee(fertile female;
diploid)
Worker bee(sterile female;
diploid)
Drone(fertile male;
haploid)
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Sexual reproduction requires fusion of sperm & egg
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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
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Some organisms are hermaphrodites; they produce both eggs and sperm & can self-fertilize
E.g., tapeworm
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Some hermaphrodites cannot self-fertilize and so must exchange
sperm to fertilize each other’s eggs
E.g., some snails
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Most animals are dioecious, with separate females and males
Female mallard Male mallard
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• Females produce large, non-motile eggs, that contain food reserves
• Males produce small, motile sperm, with no food reserves
Most animals are dioecious, with separate females and males
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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)
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Grunion spawning
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Coral spawning
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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
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Internal fertilization• Important adaptation to life on land
• Fertilization occurs inside female’s body
• Copulation: Male deposits sperm directly into female’s reproductive tract
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Internal fertilization
Damselflies mating