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© 2010 Pearson Education, Inc.
Reproduction and Development
Unifying Comcepts of Animal Reproduction
Human Reproduction
Reproductive Health
Human Development
Reproductive Technologies
© 2010 Pearson Education, Inc.
UNIFYING CONCEPTS OF ANIMAL REPRODUCTION• Reproduction is the creation of new individuals from existing
ones.
© 2010 Pearson Education, Inc.
Asexual Reproduction• Asexual reproduction creates offspring that are genetically
identical to the parent.
© 2010 Pearson Education, Inc.
• Budding, a type of asexual reproduction, produces offspring by the outgrowth and eventual splitting off of a new individual from the parent.
Bud
Figure 26.1
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• During the asexual process of fission, a parent separates into two or more offspring of about equal size.
Figure 26.2
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• 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
Number of chromosomesin body cells
Indian muntjac deer
Species
Opossum
Koala
Human
Mouse
Giraffe
Buffalo
Dog
Red viscacha rat
Duck-billed platypus
102
78
60
54
46
40
30
22
16
6
Figure 8.2
© 2010 Pearson Education, Inc.
• Asexual reproduction
– Allows a population to perpetuate itself if its individual members are isolated from one another
– Permits organisms to multiply quickly
© 2010 Pearson Education, Inc.
• However, asexual reproduction produces genetically identical offspring, which limits a population’s chance to survive periods of environmental change.
© 2010 Pearson Education, Inc.
• Sexual reproduction involves
– The fusion of gametes (sperm and egg) from two parents
– The formation of a zygote
Sexual Reproduction
© 2010 Pearson Education, Inc.
• 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
Twooffspringarising fromasexualreproductionby fission
Eggs
Figure 26.3
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• Some species are hermaphrodites, individuals with
– Male and
– Female reproductive systems
© 2010 Pearson Education, Inc.
• The mechanics of fertilization play an important part in sexual reproduction.
– Aquatic animals typically
– Use external fertilization
– Discharge their gametes into the water
Egg
Figure 26.4
© 2010 Pearson Education, Inc.
– Most terrestrial organisms deposit sperm directly from the male into the female.
© 2010 Pearson Education, Inc.
HUMAN REPRODUCTION• Both sexes of humans have
– A pair of gonads that produce gametes
– Ducts to store and deliver the gametes
© 2010 Pearson Education, Inc.
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
Side view
Rectum
Seminalvesicle
Vasdeferens
SpermductProstategland
Anus Vas deferensEpididymisTestisScrotum
Urinary bladder
Pubic bone
Erectiletissue
Urethra
Glans
Prepuce
Penis
Urinarybladder
Prostategland
Erectiletissueof penis
Vasdeferens
Epididymis
Testis
Front view
Seminalvesicle(behind bladder)
Urethra
Scrotum
Glans ofpenis
Figure 26.5
© 2010 Pearson Education, Inc.
• 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
© 2010 Pearson Education, Inc.
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
Urinary bladder
Front view
Endometrium(lining of uterus)
Uterus
Cervix(“neck” of uterus)Vagina
OviductOvaries
Follicles
Wall of uterus
Corpus luteum
Side view
Cervix
Vagina
Rectum
Vaginal opening
Anus
Uterus
Oviduct
Ovary
Urethra
Pubic bone
Shaft
Labia majora
Labia minora
ClitorisPrepuceGlans
Urinary bladder
Side view
Cervix
Vagina
Rectum
Vaginal opening
Anus
Uterus
Oviduct
Ovary
Urethra
Pubic bone
Shaft
Labia majora
Labia minora
ClitorisPrepuceGlans
Figure 26.6
© 2010 Pearson Education, Inc.
• 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
© 2010 Pearson Education, Inc.
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
© 2010 Pearson Education, Inc.
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.
Seminiferoustubule
Penis
Testis
TestisScrotum
Epididymis
Crosssection ofseminiferous tubule
Mature sperm released intocenter of seminiferous tubule
Differentiation andonset of meiosis
Diploid cell
Meiosis
Meiosis completed (diploid)
(haploid)
Secondary spermatocyte
Primary spermatocyte
Developing sperm cells
Differentiation
(haploid)Sperm cells
2n
2n
n
n
n
nnn
nnnn
Figure 26.7
© 2010 Pearson Education, Inc.
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
Differentiation and onset of
meiosis
Diploid cell in embryo
(diploid)
(haploid)
Secondary oocyte
Primary oocyte
2n
n
2n
Completion of meiosis
and onset of meiosis
n
Entry ofsperm triggerscompletion of
meiosis n
n
arrested at prophase of meiosis ; present
at birth
arrested at metaphase of meiosis
(haploid)
Mature egg (ovum)
Firstpolar body
Secondpolar body
Secondary oocyte Ovary
A secondary oocyte beingreleased during ovulation
LM
Degeneratingcorpus luteum
Corpus luteum
Ovulatedsecondary oocyte
Rupturedfollicle
Mature follicle
Growing follicle
Primaryoocytewithin follicle
Figure 26.8
© 2010 Pearson Education, Inc.
• 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.
The Female Reproductive Cycle
© 2010 Pearson Education, Inc.
• Menstruation is
– Uterine bleeding
– Caused by the breakdown of the endometrium
© 2010 Pearson Education, Inc.
REPRODUCTIVE HEALTH• Two issues of human reproductive health are
– Contraception, the deliberate prevention of pregnancy
– Sexually transmitted diseases (STDs)
© 2010 Pearson Education, Inc.
Contraception• Contraception comes in many forms with varying degrees of
effectiveness.
© 2010 Pearson Education, Inc.
• 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.
Table 26.1b
© 2010 Pearson Education, Inc.
• 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
Figure 26.10
Spermicide
Diaphragm
Condom
Birth control pill
Table 26.1
© 2010 Pearson Education, Inc.
Sexually Transmitted Diseases• Sexually transmitted diseases (STDs) are
– Contagious diseases
– Spread by sexual contact
© 2010 Pearson Education, Inc.
• Viral STDs
– Cannot be cured but can be controlled by medications
– Include
– AIDS
– Genital herpes
– Genital warts
Co
lori
zed
TE
M
Herpes simplex virusTable 26.2e
Co
lori
zed
TE
M
PapillomavirusesTable 26.2f
© 2010 Pearson Education, Inc.
• STDs caused by bacteria, protozoans, and fungi are generally curable with drugs.
Co
lori
zed
TE
M
Chlamydia trachomatis
Co
lori
zed
TE
M
Neisseria gonorrhoeae
Co
lori
zed
SE
M
Treponema pallidum
Co
lori
zed
TE
M
Herpes simplex virus
Co
lori
zed
TE
M
Papillomaviruses
Co
lori
zed
SE
M
Trichomonas vaginalis
Co
lori
zed
SE
M
Candida albicans
Table 26.2
© 2010 Pearson Education, Inc.
HUMAN DEVELOPMENT• Embryonic development begins with fertilization, the union of
sperm and egg to form a zygote.
© 2010 Pearson Education, Inc.
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.
© 2010 Pearson Education, Inc.
• The shape of a human sperm is streamlined, which helps it swim through fluids in the
– Vagina
– Uterus
– Oviduct
Plasma membrane
Acrosome
Head(carries genetic material)
Flagellum(used for swimming)
Mitochondrion(produces energy)
Nucleus
Figure 26.11
© 2010 Pearson Education, Inc.
• Fertilization by a sperm involves many steps.
Sperm
NucleusAcrosome
Follicle cell
n
Jellycoat
n
Acrosomalenzymes
Plasmamembrane
Eggnucleus
Egg cell
n
n
nCytoplasm
Zygotenucleus
Spermnucleus
2n
The spermsqueezesthrough cellsleft over fromthe follicle.
The sperm’sacrosomalenzymes digestthe jelly coatsurrounding theegg. The plasma
membranes of thesperm and egg fuse.
The sperm nucleus entersthe egg cytoplasm.
Co
lori
zed
SE
M
The sperm andegg chromosomesintermingle.
Figure 26.12
© 2010 Pearson Education, Inc.
Basic Concepts of Embryonic Development• The key to development is that each stage of development takes
place in a highly organized fashion.
© 2010 Pearson Education, Inc.
• 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.
© 2010 Pearson Education, Inc.
• 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.
Many cells(solid ball)
2 cellsZygote
4 cells
8 cells
Blastocyst (hollow ball)
Cross section of blastocyst
Gastrula (cross section)
EndodermMesodermEctoderm Gastrulation
Cleavage
Inner cellmass
Figure 26.13
© 2010 Pearson Education, Inc.
• 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
Figure 26.14
© 2010 Pearson Education, Inc.
• 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
Pregnancy and Early Development
© 2010 Pearson Education, Inc.
• The early stages of human development begin in the oviduct with
– Fertilization
– Cleavage
Oviduct
Ovary
Ovulation releasessecondary oocyte,which entersoviduct.
Uterus
The blastocystimplants in theendometrium.
Endometrium
The embryodevelops into ablastocyst.
Cleavage (cell division)of embryo starts.
Mature egg (ovum)is fertilized by asperm, forming azygote.
Figure 26.15-5
© 2010 Pearson Education, Inc.
• 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
Endometrium
Inner cell mass
January
Day 31
Day 10Day 6
Cavity
TrophoblastUterine cavity
(a) Day 6: Before implantation (b) Day 10: Implantation under way
Endometrium
Futureyolk sac
Uterine cavity
Blood vessel(maternal)
Trophoblast
Multiplying cells of trophoblast(future placenta)
Embryo
(c) Day 31: The embryo and its life-supportequipment
Chorionicvilli
Yolk sac
Mother’sbloodvessels
Allantois (formspart of theumbilicalcord)
Chorion
Amnion
Embryo
Placenta
Figure 26.16
© 2010 Pearson Education, Inc.
• 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
© 2010 Pearson Education, Inc.
The Stages of Pregnancy• Pregnancy is divided into three trimesters about 3 months each.
© 2010 Pearson Education, Inc.
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
14 weeks (98 days)9 weeks (63 days)5 weeks (35 days)
Amnion
Umbilical cordPlacenta
Figure 26.17a
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• 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.
20 weeks (140 days) At birth (280 days)
Figure 26.17b
Figure 26.18
© 2010 Pearson Education, Inc.
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
5 weeks (35 days)Figure 26.17c
© 2010 Pearson Education, Inc.
• 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
9 weeks (63 days)
Amnion
Umbilical cordPlacenta
Figure 26.17d
© 2010 Pearson Education, Inc.
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)
14 weeks (98 days)Figure 26.17e
20 weeks (140 days)Figure 26.17f
At birth (280 days)Figure 26.17g
© 2010 Pearson Education, Inc.
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
Dilation of the cervix
Cervix
Uterus
Placenta
Umbilical cord
Expulsion: delivery ofthe infant
Delivery of the placenta
UterusPlacenta(detaching)
Umbilical cord
Figure 26.19
© 2010 Pearson Education, Inc.
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.
© 2010 Pearson Education, Inc.
In Vitro Fertilization• In vitro fertilization (IVF) begins with
– The surgical removal of eggs
– The collection of sperm
• Fertilization happens under artificial, laboratory conditions.
In vitro fertilization
Zygote
Implantation
Collectedegg
Collectedsperm
Earlyembryo
Figure 26.20
© 2010 Pearson Education, Inc.
• IVF
– Offers choices that nature does not
– Raises many moral and legal issues
The Ethics of IVF
Evolution Connection: The “Grandmother Hypothesis”• Around age 50, human females undergo menopause, the
cessation of ovulation and menstruation.
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
• 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.