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Animal Reproduction
Chapter 46
Fission
• Separation of a parent into two or more
individuals of about the same size
Fragmentation
• Breaking of the body into pieces, some or all
of which develop into adults
Both asexual and sexual reproduction
occur in the animal kingdom
• Sexual reproduction is the creation of an
offspring by fusion of a male gamete (sperm)
and female gamete (egg) to form a zygote
• Asexual reproduction is creation of offspring
without the fusion of egg and sperm
Budding
• New individuals form from outgrowths of
existing ones
Parthenogenesis
• Development of a new individual from an
unfertilized egg
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Advantage of sex
• Sex generates variation and removes deleterious genes
• Asexual reproduction more favored in stable environments
Reproductive cycles
• Ovulation is the release of mature eggs at the
midpoint of a female cycle
• Most animals exhibit reproductive cycles
related to changing seasons
• Reproductive cycles are controlled by
hormones and environmental cues
Because daylight is often an important cue in reproduction,
climate change can decrease reproductive success
• Some organisms can
reproduce sexually or
asexually, depending
on conditions
• Asexual whiptail lizards
are descended from a
sexual species, and
females still exhibit
mating behaviors
Mates can be limiting
• Two hermaphrodites can mate, and some
hermaphrodites can self-fertilize
Sex reversal
• When male dies, largest member of harem
becomes female
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Sex reversal
External fertilization
• Oysters are male when small, and female
when large
Internal fertilization
Generally more parental care with
internal fertilization
• Ensure survival of offspring
Gamete production
• Most species have gonads
• In many insects, the female has a
spermatheca in which sperm is stored during
copulation
– Organs that produce gametes
• Simple systems do not have gonads, but
gametes form from undifferentiated tissue
Accessory
gland
Ovary
Testis
– Annelids
Oviduct
• More elaborate systems include sets of
accessory tubes and glands that carry,
nourish, and protect gametes and developing
embryos
Spermatheca
Vas
deferens
Ejaculatory
duct
Seminal
vesicle
Uterus
Accessory
gland
Penis and
claspers
(a) Male fruit fly
Vulva
(b) Female fruit fly
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Cloaca
• Common opening between the external
environment and the digestive, excretory, and
reproductive systems
Monogamy is rare
• Mechanisms have evolved to decrease the
chance of their mate mating with another
individual
– Found in nonmammalian vertebrates
Females can influence the relative
reproductive success of their mates
Female reproductive anatomy
Ovaries
Male reproductive anatomy
• Each ovary contains many follicles, which
consist of a partially developed egg, called an
oocyte, surrounded by support cells
• Once a month, an oocyte develops into an
ovum (egg) by the process of oogenesis
• Ovulation expels an egg cell from the follicle,
the cells of which produce estradiol prior to
ovulation
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Testes
Accessory glands
• The male gonads consist of highly coiled tubes
surrounded by connective tissue
• Sperm form in these seminiferous tubules
• Production of normal sperm cannot occur at
the body temperatures of most mammals
• Semen is composed of sperm plus secretions
from three sets of accessory glands
• The two seminal vesicles contribute about 60% of
the total volume of semen
• The prostate gland secretes its products directly
into the urethra through several small ducts
• The bulbourethral glands secrete a clear mucus
before ejaculation that neutralizes acidic urine
remaining in the urethra
Gametogenesis
• Gametogenesis, the production of gametes,
differs in male and female, reflecting the distinct
structure and function of their gametes
• Spermatogenesis, the development of sperm, is
continuous and prolific
– millions of sperm are produced per day
– each sperm takes about 7 weeks to develop
Spermatogenesis differs from
oogenesis in three ways
– All four products of meiosis develop into sperm
while only one of the four becomes an egg
– Spermatogenesis occurs throughout adolescence
and adulthood
– Sperm are produced continuously without the
prolonged interruptions in oogenesis
• Oogenesis, the development of a mature egg, is a
prolonged process
– Immature eggs form in the female embryo
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Tropic and sex hormones regulate
mammalian reproduction
Hormonal control of the female
reproductive cycles
• Human reproduction is coordinated by hormones
from the hypothalamus, anterior pituitary, and
gonads
• Gamete production, including sexual behavior
and the development of primary and secondary
sex characteristics
• Gonadotropin-releasing hormone (GnRH) is
secreted by the hypothalamus and directs the
release of FSH and LH from the anterior pituitary
• FSH and LH regulate processes in the gonads and
the production of sex hormones
• In females, the secretion of hormones and the
reproductive events they regulate are cyclic
• Prior to ovulation, the endometrium thickens
with blood vessels in preparation for embryo
implantation
• If an embryo does not implant in the
endometrium, the endometrium is shed in a
process called menstruation
Ovarian cycle
Ovarian Cycle
• The sequential release of GnRH then FSH and
LH stimulates follicle growth
Uterine (Menstrual) Cycle
• Hormones
coordinate the
uterine cycle
with the
ovarian cycle
Menstrual versus estrous cycles
• Menstrual cycles are characteristic only of
humans and some other primates
– The endometrium is shed from the uterus in a
bleeding called menstruation
– Sexual receptivity is not limited to a time frame
• Estrous cycles are characteristic of most
mammals
– The endometrium is reabsorbed by the uterus
– Sexual receptivity is limited to a “heat” period
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Hormonal control of the male
reproductive system
In placental mammals, an embryo
develops fully within the mother’s
uterus
• An egg develops into an embryo in a series of
predictable events
Embryo implantation and gestation
• Embryo releases human chorionic
gonadotropin (hCG), which prevents
menstruation
• Duration of species’ pregnancy correlates with
body size and maturity of the young at birth
Twins
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A. she will ovulate
within one week.
B. she has not been
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D. she is undergoing
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oogenesis produces one
haploid cell and
spermatogenesis produces
four.
B. oogenesis begins at the onset
of puberty.
C. spermatogenesis begins in
the embryonic stage of
development.
D. oogenesis produces one
ovum and spermatogenesis
produces four spermatozoa.
internal fertilization allows
animals to reproduce
sexually.
B. internal fertilization requires
much less expenditure of
resources.
C. internal fertilization produces
more offspring, ensuring
rapid population growth.
D. internal fertilization prevents
the drying out of gametes in a
dry environment.
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that are identical to the parent,
since the parent’s sperm and eggs
are identical to each other.
that are different from the parent,
since the parent must use sperm
stored from a previous mating.
that are different from the parent,
because random assortment and
crossing over during meiosis can
generate a unique combination of
genes upon fertilization.
that are different from the parent,
because interactions with the
environment alter all genes.
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A.
An advantage of internal fertilization
over external fertilization is that
u.
..
A self-fertilizing hermaphrodite
produces offspring
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An infant suckling on the breast of a woman who has recently given birth
sends a nerve impulse to the pituitary gland. The pituitary gland then secretes
oxytocin, which stimulates the mammary glands in the breasts to release
milk. What type of hormonal feedback is this?
A. Negative feedback
B. Positive feedback
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