1. Chapter 46 - Animal Reproduction
Lecture Presentation by Nicole Tunbridge and
Kathleen Fitzpatrick
Unit 4: New Cells & Organisms

2. Chapter 46 - Animal Reproduction
Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom
Reproduction
Creation of an offspring
Sexual Reproduction
Fusion of a male gamete (sperm) and female gamete (egg) to form a zygote
Asexual Reproduction
No fusion of gametes.
Unit 4: New Cells & Organisms

3. Mechanisms of Asexual Reproduction
Chapter 46 - Animal Reproduction
Mechanisms of Asexual Reproduction
Budding: Simple form of asexual reproduction only among invertebrates
New individuals arise from outgrowths of existing individuals
Fission: Separation of a parent into two or more individuals of about the same size by many invertebrates
Fragmentation: Breaking of the body into pieces  some or all develop into adults
Must be accompanied by regeneration of lost parts
Parthenogenesis: Development of an unfertilized egg  a new individual
Mostly invertebrates, rarely in some vertebrates
Unit 4: New Cells & Organisms

4. Sexual Reproduction: An Evolutionary Enigma
Chapter 46 - Animal Reproduction
Sexual Reproduction: An Evolutionary Enigma
“Two-fold cost” of Sexual Reproduction
Sexual females have half as many daughters as asexual females
Almost all eukaryotic species reproduce sexually
Asexual Reproduction: Advantageous in stable, favorable environments
Sexual Reproduction: Produces genetically varied offspring  varied phenotypes  enhance reproductive success of parents when environmental factors change relatively rapidly
Unit 4: New Cells & Organisms

5. Chapter 46 - Animal Reproduction
Figure
Asexual
reproduction
Sexual
reproduction
Generation 1
Female
Female
Generation 2
Male
Generation 3
Figure The “reproductive handicap” of sex (step 3)
Generation 4
Unit 4: New Cells & Organisms

6. Chapter 46 - Animal Reproduction
Reproductive Cycles
Some organisms can reproduce sexually or asexually, depending on conditions
Controlled by hormones and/or environmental cues
Most animals exhibit cycles correlate with seasons
Climate change can decrease reproductive success
Seasonal temperature is often an important reproductive cue
Ovulation: Release of mature eggs triggered by hormones at midpoint of female cycle
Several genera of fishes, amphibians, and lizards reproduce only by parthenogenesis
Unit 4: New Cells & Organisms

7. Chapter 46 - Animal Reproduction
Figure 46.4
(a) A. uniparens females
Ovary
size
Ovulation
Ovulation
Progesterone
Estradiol
Hormone
level
Figure 46.4 Sexual behavior in parthenogenetic lizards
Time
Behavior:
Female
Male-
like
Female
Male-
like
(b)
The changes in sexual behavior of A. uniparens
individuals are correlated with the cycles of
ovulation.
Unit 4: New Cells & Organisms

8. Variation in Patterns of Sexual Reproduction
Chapter 46 - Animal Reproduction
Variation in Patterns of Sexual Reproduction
Hermaphroditism
Finding a mate for reproduction may be challenging
Solution: Hermaphroditism
Each individual has male & female reproductive systems
2 hermaphrodites can mate
some hermaphrodites can self-fertilize
Individuals of some species undergo sex reversals
Male  Female
Female  Male
Unit 4: New Cells & Organisms

9. Chapter 46 - Animal Reproduction
Concept 46.2: Fertilization depends on mechanisms that bring together sperm and eggs of the same species
Fertilization: Union of egg + sperm
External Fertilization:
Eggs shed by the female
Fertilized by sperm in the external environment
Moist habitat is always required for external fertilization
Allows sperm to swim to the egg
Prevents the gametes from drying out
Some species exhibit spawning, triggered by chemical signals or environmental cues.
Individuals cluster in the same area to release gametes into water simultaneously.
Unit 4: New Cells & Organisms

10. Internal Fertilization
Chapter 46 - Animal Reproduction
Internal Fertilization
Requires behavioral interactions
Requires compatible copulatory organs
Sperm deposited in or near the female reproductive tract
Fertilization occurs within the tract
Fertilization timing mediated by environmental cues, pheromones, and/or courtship behaviors
Unit 4: New Cells & Organisms

11. Ensuring the Survival of Offspring
Chapter 46 - Animal Reproduction
Ensuring the Survival of Offspring
Internal Fertilization
Yields fewer gametes than external fertilization
Survival % of zygotes higher
Mechanisms provide protection of embryos
Parental care of young helps ensure survival of offspring
Some Terrestrial Animals: Embryos develop in eggs
Ca/protein-containing shells & internal membranes
Other animals retain embryo: Develops inside female
Unit 4: New Cells & Organisms

12. Gamete Production and Delivery
Chapter 46 - Animal Reproduction
Gamete Production and Delivery
Gamete production required for sexual reproduction
Most species have gonads to produce gametes
Simple systems lack gonads
Gametes form from undifferentiated tissue
Elaborate systems include accessory tubes & glands
Carry, nourish, and protect gametes/developing embryos
Insects have separate sexes & complex systems
Female has a spermatheca
Sperm stored during copulation
Unit 4: New Cells & Organisms

13. Chapter 46 - Animal Reproduction
Figure 46.7
Accessory
gland 1
Testis 2
Vas deferens 4
Ejaculatory
duct 3
Seminal
vesicle 5
Penis and
claspers
(a) Male fruit fly 1
Ovary
Figure 46.7 Insect reproductive anatomy 2
Oviduct
Spermatheca
Accessory
gland
Uterus 3
Vulva
(b) Female fruit fly
Unit 4: New Cells & Organisms

14. Chapter 46 - Animal Reproduction
Cloaca
Opening between external environment and the digestive, excretory, and reproductive systems
Common in nonmammalian vertebrates
Mammals: Separate opening to the digestive tract
Monogamy: Rare among animals
Males and/or females of some species evolved mechanisms to decrease chance of the mate mating with another individual
Females can influence relative reproductive success of mates
Unit 4: New Cells & Organisms

15. Concept 46.3: Reproductive organs produce and transport gametes
Chapter 46 - Animal Reproduction
Concept 46.3: Reproductive organs produce and transport gametes
Human Male Reproductive Structures
Gonads: Produce sperm and hormones
Seminiferous Tubules: Site of sperm formation
Leydig Cells: Produce hormones
Scattered between the tubules
Production of healthy sperm cannot occur at the body temperatures of most mammals
Accessory Glands: Secrete products needed for sperm movement
Ducts: Carry sperm and glandular secretions
Unit 4: New Cells & Organisms

16. Human Female Reproductive Structures
Chapter 46 - Animal Reproduction
Human Female Reproductive Structures
Gonads: Ovaries (abdominal cavity)
Contains follicles with oocytes surrounded by support cells
Oocyte: A partially developed egg
Oviduct: Egg cell travels as cilia convey ovary  uterus
Travels via fallopian tubes
Mammary Glands: Small sacs of epithelial tissue secrete milk
Not part of the reproductive system
Unit 4: New Cells & Organisms

17. Chapter 46 - Animal Reproduction
Gametogenesis
Gametogenesis: Production of gametes
Spermatogenesis: Formation of sperm,
Continuous & prolific
Hundreds of millions of sperm are produced per day
Each sperm takes about 7 weeks to develop
Oogenesis: Development of a mature egg
Prolonged process
Immature eggs form in the female embryo
Development completed years, or decades later
Unit 4: New Cells & Organisms

18. Chapter 46 - Animal Reproduction
Epididymis
Primordial germ
cell in embryo
Seminiferous
tubule
Key
Diploid (2n)
Mitotic divisions
Haploid (n)
Spermatogonial
stem cell 2n
Lumen
Mitotic divisions
Testis
Spermatogonium 2n
Mitotic divisions
Sertoli cell
nucleus
Primary
spermatocyte 2n
Meiosis I
Secondary
spermatocyte n n
Spermatids
Meiosis II
Figure 46.11a Exploring human gametogenesis (part 1: spermatogenesis)
Early
spermatid n n n n
Neck
Tail
Plasma
membrane
Midpiece
Head
Differentiation
Lumen of
seminiferous
tubule
Nucleus
Sperm cell n n n n
Acrosome
Mitochondria
Unit 4: New Cells & Organisms

19. Chapter 46 - Animal Reproduction
Primordial germ cell
Ovary
Mitotic divisions
Follicle 2n
Oogonium
Primary oocyte
within follicle
Mitotic divisions
Primary oocyte
(present at birth), arrested
in prophase of meiosis I 2n
Growing
follicle
IN EMBRYO
STARTING AT
PUBERTY
Completion of meiosis I
and onset of meiosis II n n
Secondary oocyte,
arrested at metaphase
of meiosis II
First
polar
body
Mature follicle
Ovulation, sperm entry
Ruptured
follicle
Completion of meiosis II
Second
polar
body
Figure 46.11b Exploring human gametogenesis (part 2: oogenesis) n
Ovulated
secondary oocyte n
Fertilized egg
Corpus luteum
Degenerating
corpus luteum
Unit 4: New Cells & Organisms

20. Spermatogenesis vs. Oogenesis
All four products of meiosis develop into sperm
Occurs throughout adolescence & adulthood
Sperm are produced continuously
Only one of the four products of meiosis becomes an egg
Begins in fetus, matures years later
Prolonged interruptions in egg development

21. Chapter 46 - Animal Reproduction
Human gametogenesis
Spermatogenesis
Oogenesis
Primary
spermatocyte
Primary
oocyte 2n 2n n
Polar body
Secondary
spermatocytes
Secondary
oocyte n n n n n n n
Spermatids
Sperm n n n n
Figure 46.UN03 Summary of key concepts: human gametogenesis n
Polar body
Fertilized
egg n
Unit 4: New Cells & Organisms

22. Chapter 46 - Animal Reproduction
Concept 46.4: The interplay of tropic and sex hormones regulates mammalian reproduction
Humans: Coordinated by hormones secreted by hypothalamus, anterior pituitary, and gonads
Gamete production, mating behavior, development of primary & secondary sex characteristics
Gonadotropin-releasing hormone (GnRH):
Secreted by hypothalamus
Directs the release of FSH (follicle-stimulating hormone) and LH (luteinizing hormone)
From the anterior pituitary
Regulate processes in gonads & production of sex hormones
Testosterone: Main androgen (steroid)
Estrogens: Estradiol & Progesterone (steroid)
Unit 4: New Cells & Organisms

23. Hormonal Control of Male Reproductive System
Chapter 46 - Animal Reproduction
Hormonal Control of Male Reproductive System
Testosterone regulates the production of GnRH, FSH, and LH through negative feedback mechanisms
FSH promotes activity of Sertoli cells
Nourish developing sperm
Sertoli Cells: Secrete inhibin (hormone)
Reduces FSH secretion from the anterior pituitary
LH regulates Leydig cells
Secrete testosterone and other androgens
Promotes spermatogenesis
Unit 4: New Cells & Organisms

24. Chapter 46 - Animal Reproduction
Figure 46.13
Chapter 46 - Animal Reproduction
Hypothalamus
GnRH
Anterior pituitary
FSH LH
Negative feedback
Negative feedback
Sertoli cells
Leydig cells
Figure Hormonal control of the testes
Inhibin
Testosterone
Spermatogenesis
TESTIS
Unit 4: New Cells & Organisms

25. Hormonal Control of Female Reproductive Cycles
Chapter 46 - Animal Reproduction
Hormonal Control of Female Reproductive Cycles
Secretion of hormones and regulated reproductive events are cyclic
Ovarian Cycle
GnRH released  FSH & LH stimulate follicle growth
Estradiol increases  secondary oocyte released
Follicular tissue  corpus luteum  secretes progesterone and estradiol  negative feedback on hypothalamus and pituitary
Uterine Cycle
Secretion of nutrients, shedding of the endometrium coordinates with growth of new ovarian follicles
New cycle begins if no embryo implantation
Unit 4: New Cells & Organisms

26. Chapter 46 - Animal Reproduction
Menopause
After ~500 cycles, human females ovulation and menstruation ceases.
Rare among animals
May have evolved to allow a mother to provide better care for her children and grandchildren
Perhaps humans are living beyond their intended biological lifespans?
Unit 4: New Cells & Organisms

27. Menstrual Versus Estrous Cycles
Chapter 46 - Animal Reproduction
Menstrual Versus Estrous Cycles
Menstrual Cycles
Characteristic only of humans and some other primates
Estrous Cycles
Characteristic of most mammals
Sexual receptivity is limited to a “heat” period called estrus
Length and frequency of estrous cycles vary by species
Unit 4: New Cells & Organisms

28. Chapter 46 - Animal Reproduction
Figure 46.15 3
Cleavage 4
Cleavage
continues.
Ovary 2
Fertilization
Uterus 5
Implantation 1
Ovulation
Figure Formation of a human zygote and early postfertilization events
Endometrium
Unit 4: New Cells & Organisms

29. Chapter 46 - Animal Reproduction
Concept 46.5: In placental mammals, an embryo develops fully within the mother’s uterus
Conception, Embryonic Development, and Birth
Conception: Fertilization of egg by sperm in oviduct
Zygote divides by mitosis (cleavage)  blastocyst  embryo implants
Blastocyst: Ball of cells with central cavity
Pregnancy/Gestation: Carrying 1 or more embryos in the uterus
Duration of pregnancy correlates with body size and maturity of the young at birth in most species
Human Gestation: ~9 months (3 equal trimesters)
Unit 4: New Cells & Organisms

30. Maternal Immune Tolerance of the Embryo and Fetus
Chapter 46 - Animal Reproduction
Maternal Immune Tolerance of the Embryo and Fetus
A woman’s acceptance of her “foreign” offspring is not fully understood
May be due to suppression of immune response in her uterus
Unit 4: New Cells & Organisms

31. Chapter 46 - Animal Reproduction
Figure 46.17
(a) 5 weeks
Figure Some stages of human development during the first and second trimesters
(b) 14 weeks
(c) 20 weeks
Unit 4: New Cells & Organisms

32. Chapter 46 - Animal Reproduction
First Trimester
Most radical changes for both mother and embryo
Implanted embryo secretes hormones  regulate mother’s reproductive system
Human Chorionic Gonadotropin (hCG): Maintains secretion of progesterone and estrogens
Organogenesis: Development of the body organs
Embryo  Fetus: Many major structures present
Not all embryos capable of completing development
Many spontaneously stop due to chromosomal or developmental abnormalities
Ectopic Pregnancy: Fertilized egg lodges in fallopian tube  Can be fatal.
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33. Early Embryonic Development
Chapter 46 - Animal Reproduction
Early Embryonic Development
At 2-4 weeks: Embryo obtains nutrients directly from endometrium
Trophoblast: Outer layer of blastocyst
Endometrium + Trophoblast  Placenta
Monozygotic Twins (Genetically Identical)
Splitting of embryo during 1st month of development
Dizygotic (Fraternal) Twins (Genetically Distinct)
Release and fertilization of two eggs
Unit 4: New Cells & Organisms

34. Second and Third Trimesters
Chapter 46 - Animal Reproduction
Second and Third Trimesters
Second Trimester
The fetus grows and is very active  mother may feel fetal movements
Uterus grows  pregnancy shows
Third Trimester
Fetus grows and fills the space within the embryonic membranes
Childbirth
Labor is regulated by prostaglandins, estradiol, and oxytocin
Unit 4: New Cells & Organisms

35. Chapter 46 - Animal Reproduction
Figure 46.18
Estradiol
Oxytocin
from
ovaries
from fetus
and mother’s
posterior pituitary
Activates oxytocin
receptors on uterus
Stimulates uterus
to contract
Positive feedback
Stimulates
placenta to make
Figure Positive feedback in labor
Prostaglandins
Stimulate more
contractions
of uterus
Unit 4: New Cells & Organisms

36. Chapter 46 - Animal Reproduction
Contraception
Deliberate prevention of pregnancy:
Preventing release of eggs and sperm
Keeping sperm and egg apart
Preventing implantation of an embryo
Method of Contraception
How it works…
Or does it?
Rhythm Method
Refrain from intercourse around ovulation.
10–20%
Coitus Interruptus
Withdrawal before ejaculation.
UNRELIABLE
Barrier Methods
Use of condom or diaphragm.
10%
Intrauterine Devices (IUDs)
Device interferes with implantation; increases risk of ectopic pregnancy.
less than 1%
Female Birth Control Pills
Hormones suppress ovulation.
Sterilization
Tubal Ligation: Ties off the oviducts
Vasectomy: Ties off the vas deferens
Almost 0%!
Unit 4: New Cells & Organisms

37. Chapter 46 - Animal Reproduction
Figure 46.20
Chapter 46 - Animal Reproduction
MALE
FEMALE
Method
Event
Event
Method
Production of
sperm
Production of
primary oocytes
Vasectomy
Combination
birth control
pill (or injection,
patch, or
vaginal ring)
Sperm transport
down male
duct system
Oocyte
development
and ovulation
Abstinence
Abstinence
Condom
Female condom
Coitus
interruptus
(very high
failure rate)
Sperm
deposited
in vagina
Capture of the
oocyte by the
oviduct
Tubal ligation
Spermicides;
diaphragm;
progestin alone
(as minipill
or injection)
Sperm movement
through female
reproductive
tract
Transport
of oocyte in
oviduct
Figure Mechanisms of several contraceptive methods
Meeting of sperm and oocyte
in oviduct
Morning-after pill;
intrauterine device (IUD)
Union of sperm and egg
Implantation of blastocyst
in endometrium
Unit 4: New Cells & Organisms

38. Infertility and In Vitro Fertilization
Chapter 46 - Animal Reproduction
Infertility and In Vitro Fertilization
Causes vary greatly with men and women equally
Preventable Causes
STDs are most significant
In vitro fertilization (IVF):
Mixes eggs with sperm in culture dishes
Returns embryo to uterus at 8-cell stage
Sperm, or sperm nuclei, can also be injected directly into an oocyte
Unit 4: New Cells & Organisms

39. In vitro Fertilization
Chapter 46 - Animal Reproduction
In vitro Fertilization
Figure In vitro fertilization (IVF)
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40. Detecting Disorders During Pregnancy
Chapter 46 - Animal Reproduction
Detecting Disorders During Pregnancy
Noninvasive Procedures
Ultrasound imaging
Invasive Procedures
Amniocentesis & Chorionic Villus Sampling
Amniotic fluid or fetal cells obtained for genetic testing
Genetic testing of fetus poses ethical questions
Presents parents with difficult decisions
Almost all detectable disorders are untreatable in the uterus
Many disorders cannot be corrected after birth
CRISP-Cas9
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41. Chapter 46 - Animal Reproduction
Abortion is the termination of a pregnancy
Miscarriage: Spontaneous abortion
Occurs in up to 1/3 of all pregnancies
Common during the first trimester
Drug-induced: Nonsurgical
RU486 terminates a pregnancy within first 7-weeks
Prior to full development of the fetus.
Unit 4: New Cells & Organisms