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Reproduction and Development
Unifying Comcepts of Animal Reproduction
Human Reproduction
Reproductive Health
Human Development
Reproductive Technologies
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UNIFYING CONCEPTS OF ANIMAL
REPRODUCTION
• Reproduction is the creation of new individuals from existing
ones.
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Asexual Reproduction
• Asexual reproduction creates offspring that are genetically
identical to the parent.
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• Budding, a type of asexual reproduction, produces offspring by
the outgrowth and eventual splitting off of a new individual from
the parent.
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Bud
Figure 26.1
• During the asexual process of fission, a parent separates into two
or more offspring of about equal size.
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Figure 26.2
• Fragmentation is the breaking of a parent body into several
pieces.
• Regeneration
– Typically follows fragmentation
– Is the regrowth of a whole animal from the pieces
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Species
Indian muntjac deer
Koala
Opossum
Giraffe
Mouse
Human
Duck-billed platypus
Buffalo
Dog
Red viscacha rat
Number of chromosomes
in body cells
6
16
22
30
40
46
54
60
78
102
Figure 8.2
• Asexual reproduction
– Allows a population to perpetuate itself if its individual members are
isolated from one another
– Permits organisms to multiply quickly
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• However, asexual reproduction produces genetically identical
offspring, which limits a population’s chance to survive periods of
environmental change.
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Sexual Reproduction
• Sexual reproduction involves
– The fusion of gametes (sperm and egg) from two parents
– The formation of a zygote
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• Sexual reproduction increases the
– Genetic variability among offspring
– Chances that some of the variants can survive and reproduce
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• Some animals can reproduce both
– Sexually and
– Asexually
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Eggs
Two
offspring
arising from
asexual
reproduction
by fission
Figure 26.3
• Some species are hermaphrodites, individuals with
– Male and
– Female reproductive systems
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• The mechanics of fertilization play an important part in sexual
reproduction.
– Aquatic animals typically
–
Use external fertilization
–
Discharge their gametes into the water
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Egg
Figure 26.4
– Most terrestrial organisms deposit sperm directly from the male into the
female.
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HUMAN REPRODUCTION
• Both sexes of humans have
– A pair of gonads that produce gametes
– Ducts to store and deliver the gametes
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Male Reproductive Anatomy
• The penis
– Contains erectile tissue that fills with blood
– Becomes erect during sexual arousal
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• The male gonads are the testes, which
– Are enclosed in a sac called the scrotum
– Produce sperm
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Side view
Rectum
Seminal
vesicle
Front view
Urinary bladder
Vas
deferens
Anus
Erectile
tissue
Urethra
Vas deferens
Epididymis
Testis
Scrotum
Glans
Seminal
vesicle
(behind
bladder)
Prostate
gland
Pubic bone
Sperm
duct
Prostate
gland
Urinary
bladder
Penis
Erectile
tissue
of penis
Urethra
Vas
deferens
Scrotum
Glans of
penis
Prepuce
Epididymis
Testis
Figure 26.5
• During an ejaculation, the seminal vesicles and prostate gland
add fluid that
– Nourishes the sperm
– Provides protection from the natural acidity of the vagina
• Semen consists of
– This fluid and
– Sperm
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Female Reproductive Anatomy
• The outer features of the female reproductive tract are the vulva,
consisting of the
– Vagina, or birth canal
– Labia majora, fatty ridges that protect the entire genital region
– Labia minora, inner folds bordering the openings
– Hymen, partially covering the vaginal opening
– Clitoris, which becomes erect upon sexual arousal
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Oviduct
Ovary
Uterus
Side view
Urinary bladder
Rectum
Pubic bone
Cervix
Urethra
Shaft
Glans
Clitoris
Prepuce
Labia minora
Vagina
Anus
Vaginal opening
Labia majora
Oviduct
Ovaries
Front view
Follicles
Uterus
Corpus luteum
Wall of uterus
Vagina
Endometrium
(lining of uterus)
Cervix
(“neck” of uterus)
Figure 26.6
• The ovaries
– Are the sites of gamete production
– Contain follicles consisting of a single egg surrounded by layers of cells
that nourish and protect it
• The follicles also produce estrogen, the female sex hormone.
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• During ovulation an egg is
– Ejected from a follicle
– Collected into the oviduct, where fertilization typically occurs
• The remains of the follicle grow to form a solid mass, the corpus
luteum, which releases hormones during the reproductive cycle.
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• The uterus
– Is the actual site of pregnancy
– Is lined by a thick blood-rich layer of tissue, the endometrium, where an
embryo implants and grows
• A developing human is called
– An embryo for the first nine weeks
– A fetus from the 9th week until birth
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• The cervix
– Is the narrow neck at the bottom of the uterus
– Opens into the vagina
• Annual Pap smears:
– Sample cervical cells
– Can detect cervical cancer early, when treatment is more likely to be
successful
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Gametogenesis
• Gametogenesis produces gametes, haploid cells, by meiosis.
• In females, it’s called oogenesis. Most eggs are formed before
birth
• In males, it’s called spermatogenesis and continues from puberty
to death
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Spermatogenesis
• Spermatogenesis
– Is the formation of sperm cells
– Occurs in seminiferous tubules inside the testes
• Primary spermatocytes are diploid cells that undergo meiosis
and produce secondary spermatocytes.
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Epididymis
Testis
Scrotum
Penis
Diploid cell
2n
Testis
Seminiferous
tubule
Differentiation and
onset of meiosis 
Primary spermatocyte
2n
Meiosis  completed
n
(diploid)
Cross
section of
seminiferous tubule
Secondary spermatocyte
n
(haploid)
Meiosis 
n
n
n
n
Developing sperm cells
Differentiation
n
n
n
n
Sperm cells
(haploid)
Mature sperm released into
center of seminiferous tubule
Figure 26.7
Oogenesis
• Oogenesis is the development of eggs within the ovaries.
• Meiosis I produces
– A secondary oocyte
– A polar body
• Meiosis II produces
– A mature ovum
– A polar body
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Primary
oocyte
within
follicle
Growing
follicle
2n
Diploid cell
in embryo
Mature follicle
Differentiation
and onset of
meiosis 
Secondary
oocyte
Ovary
Ruptured
follicle
2n
n
n
Ovulated
secondary oocyte
polar body
A secondary oocyte being
released during ovulation
Secondary oocyte
n
Entry of
sperm triggers
completion of
meiosis 
(diploid)
arrested at prophase
of meiosis ; present
at birth
First
LM
Completion
of meiosis 
and onset of
meiosis 
Primary oocyte
(haploid)
arrested at metaphase
of meiosis 
Corpus luteum
n
Second
polar body
Mature egg (ovum)
(haploid)
Degenerating
corpus luteum
Figure 26.8
The Female Reproductive Cycle
•
•
•
Human females have a reproductive cycle, a recurring series of
events that
–
Produces gametes
–
Makes females available for fertilization
–
Prepares the body for pregnancy
The female reproductive cycle is actually two cycles in one:
–
The ovarian cycle controls the growth and release of an egg.
–
The menstrual cycle prepares the uterus for possible implantation of
an embryo.
Hormones regulate the ovarian and menstrual cycle.
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• Menstruation is
– Uterine bleeding
– Caused by the breakdown of the endometrium
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REPRODUCTIVE HEALTH
• Two issues of human reproductive health are
– Contraception, the deliberate prevention of pregnancy
– Sexually transmitted diseases (STDs)
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Contraception
• Contraception comes in many forms with varying degrees of
effectiveness.
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• Barrier methods prevent sperm from meeting an egg. These
include
– Diaphragms, a dome-shaped rubber cap that covers the cervix
– Condoms, sheaths usually made of latex, that fit
–
Over the penis or
–
Within the vagina
• Barrier devices are usually used with spermicides, sperm-killing
chemicals.
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Table 26.1b
• Birth control hormones include
– Oral contraceptives, or birth control pills, which have been used by
millions of women since the 1960s
– Morning-after pills (MAPs), which are about 75% effective at preventing
pregnancy when taken within three days of intercourse
– RU-486, which can induce abortions
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Figure 26.10
Spermicide
Diaphragm
Condom
Birth control pill
Table 26.1
Sexually Transmitted Diseases
• Sexually transmitted diseases (STDs) are
– Contagious diseases
– Spread by sexual contact
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• Viral STDs
– Cannot be cured but can be controlled by medications
– Include
–
AIDS
–
Genital herpes
–
Genital warts
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Colorized TEM
Herpes simplex virus
Table 26.2e
Colorized TEM
Papillomaviruses
Table 26.2f
• STDs caused by bacteria, protozoans, and fungi are generally
curable with drugs.
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Colorized TEM
Herpes simplex virus
Papillomaviruses
Colorized SEM
Treponema pallidum
Trichomonas vaginalis
Colorized SEM
Neisseria gonorrhoeae
Colorized TEM
Colorized SEM
Colorized TEM
Colorized TEM
Chlamydia trachomatis
Candida albicans
Table 26.2
HUMAN DEVELOPMENT
• Embryonic development begins with fertilization, the union of
sperm and egg to form a zygote.
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Fertilization
• Sexual intercourse releases hundreds of millions of sperm into
the vagina.
– Only a few hundred survive the trip to the egg.
– Only one will fertilize it.
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• The shape of a human sperm is streamlined, which helps it swim
through fluids in the
– Vagina
– Uterus
– Oviduct
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Head
(carries genetic material)
Plasma membrane
Mitochondrion Nucleus
(produces energy)
Acrosome
Flagellum
(used for swimming)
Figure 26.11
• Fertilization by a sperm involves many steps.
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The plasma
membranes of the
sperm and egg fuse.
The sperm nucleus enters
the egg cytoplasm.
Acrosomal
enzymes
Sperm
Nucleus
Acrosome
n
n
n
Cytoplasm
Follicle
cell
Colorized SEM
The sperm
squeezes
through cells
left over from
the follicle.
The sperm’s
acrosomal
enzymes digest
the jelly coat
surrounding the
egg.
Jelly
coat
Egg cell
Plasma
membrane
n
Sperm
nucleus
2n
n
Egg
nucleus
The sperm and
egg chromosomes
intermingle.
Zygote
nucleus
Figure 26.12
Basic Concepts of Embryonic Development
• The key to development is that each stage of development takes
place in a highly organized fashion.
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• Development begins with cleavage, a series of rapid cell divisions
that results in a multicellular ball.
• Cleavage continues as the embryo moves down the oviduct
toward the uterus.
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• A blastocyst
– Forms about 6–7 days after fertilization
– Consists of a fluid-filled hollow ball with:
–
About 100 cells
–
A small clump of inner cells called the inner cell mass, which
eventually forms the fetus
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• About 9 days after conception, the embryo
– Undergoes gastrulation, an organized migration of cells
– Changes to a gastrula stage with three main tissue layers that establish
the basic body plan:
–
Ectoderm is the outer layer that forms the nervous system and
skin.
–
Mesoderm is the middle layer that forms the heat, kidneys, and
muscles.
–
Endoderm is the innermost layer the becomes the lining of the
digestive tract.
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Zygote
2 cells
4 cells
Cleavage
8 cells
Inner cell
mass
Many cells
(solid ball)
Blastocyst
(hollow ball)
Ectoderm
Mesoderm
Endoderm
Cross section
of blastocyst
Gastrulation
Gastrula
(cross section)
Figure 26.13
• Tissues and organs take shape in a developing embryo as a result
of many different changes in the cells.
• In the process called induction, one group of cells influences the
development of an adjacent group of cells.
• Programmed cell death:
– Selectively kills cells to reshape the embryo
– Is used to form the fingers of the human hand
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Figure 26.14
Pregnancy and Early Development
•
Pregnancy, or gestation, is
–
The carrying of developing young within the female reproductive
tract
–
Measured as 40 weeks from the start of the last menstrual cycle in
humans
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• The early stages of human development begin in the oviduct
with
– Fertilization
– Cleavage
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The embryo
develops into a
blastocyst.
Cleavage (cell division)
of embryo starts.
Oviduct
Mature egg (ovum)
is fertilized by a
sperm, forming a
zygote.
Ovary
The blastocyst
implants in the
endometrium.
Ovulation releases
secondary oocyte,
which enters
oviduct.
Endometrium
Uterus
Figure 26.15-5
• About one week after conception
– The embryo has become a blastocyst.
– The blastocyst implants in the uterine wall.
– The outer embryonic cell layer, the trophoblast, starts to form part of
the placenta, the organ that
–
Provides nourishment and oxygen to the embryo
–
Helps dispose of metabolic waste
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January
Day 6 Day 10
Day 31
Endometrium
Endometrium
Inner cell mass
Embryo
Future
yolk sac
Cavity
Placenta
Allantois (forms
part of the
umbilical
cord)
Blood
vessel
(maternal)
Multiplying cells
of trophoblast
(future placenta)
Trophoblast
Trophoblast
(a) Day 6: Before implantation
Uterine cavity
Yolk
sac
Mother’s
blood
vessels
Amnion
Embryo
Chorion
Chorionic
villi
Uterine cavity
(b) Day 10: Implantation under way
(c) Day 31: The embryo and its life-support
equipment
Figure 26.16
• About a month after conception
–
The placenta has fingerlike chorionic villi that promote exchanges
between the embryo’s and mother’s blood
–
Four life-supporting membranes have formed:
– Amnion, a fluid-filled sac that protects the embryo
– Yolk sac, which produces the first blood cells
– Allantois, which helps form the umbilical cord
– Chorion, which contributes to the placenta
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The Stages of Pregnancy
• Pregnancy is divided into three trimesters about 3 months each.
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The First Trimester
• About 5 weeks after fertilization, the embryo
– Has formed a brain and spinal cord
– Has developed four stumpy limb buds
– Has a short tail
– Has pharyngeal pouches
– Has genitals that can be examined to determine the sex by an ultrasound
device
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Amnion
Placenta
5 weeks (35 days)
Umbilical cord
9 weeks (63 days)
14 weeks (98 days)
Figure 26.17a
• About 9 weeks after fertilization:
– The embryo has all of its organs and major body parts.
– The limb buds have become tiny arms and legs with fingers and toes.
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20 weeks (140 days)
At birth (280 days)
Figure 26.17b
Figure 26.18
The Second Trimester
• At about 14 weeks of development, the fetus
– Is about 2.4 inches long
– Starts to look distinctly human
• At about 20 weeks of development, the embryo
– Is now called a fetus
– Mostly reveals an increase in
–
Size
–
Detail
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5 weeks (35 days)
Figure 26.17c
• At 20 weeks, the fetus
– Is about 19 cm (7.6 in.) long
– Weighs about half a kilogram (1 lb)
– Has the face of an infant
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Amnion
Placenta
Umbilical cord
9 weeks (63 days)
Figure 26.17d
The Third Trimester
• The third trimester
– Is a time of rapid growth
– Includes many important physical changes
• At birth, a typical baby
– Is about 50 cm (20 in.) long
– Weighs 2.7–4.5 kg (6–10 lb)
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14 weeks (98 days)
Figure 26.17e
20 weeks (140 days)
Figure 26.17f
At birth (280 days)
Figure 26.17g
Childbirth
• The birth of a child is brought about by a series of strong,
rhythmic contractions of the uterus called labor.
• Hormones such as oxytocin, a powerful stimulant of the smooth
muscle walls in the uterus, play a key role in inducing labor.
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• Labor involves three stages:
– (1) Dilation:
–
The longest stage of labor
–
Increases the opening of the cervix
– (2) Expulsion results in the delivery of the child
– (3) Delivery of the placenta, about 15 minutes after the birth of the baby
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Uterus
Placenta
(detaching)
Placenta
Umbilical cord
Uterus
Cervix
Umbilical cord
Dilation of the cervix
Expulsion: delivery of
the infant
Delivery of the placenta
Figure 26.19
Infertility
• Infertility is
– The inability to have children after one year of trying
– Most often due to problems in the man, such as underproduction of
sperm or impotence
– Sometimes caused by impotence (erectile dysfunction), the inability to
maintain an erection
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• Female infertility can result from
– A lack of eggs
– A failure to ovulate
• There are technologies available to help treat the many forms of
infertility.
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In Vitro Fertilization
• In vitro fertilization (IVF) begins with
– The surgical removal of eggs
– The collection of sperm
• Fertilization happens under artificial, laboratory conditions.
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Implantation
Zygote
Early
embryo
Collected
egg
In vitro fertilization
Collected
sperm
Figure 26.20
The Ethics of IVF
• IVF
– Offers choices that nature does not
– Raises many moral and legal issues
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Evolution Connection:
The “Grandmother Hypothesis”
• Around age 50, human females undergo menopause, the
cessation of ovulation and menstruation.
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• How might menopause be adaptive?
• Menopause might increase a woman’s fitness by allowing her to
invest more time and energy in her children and grandchildren
instead of having more children.
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