Transcript 46.2 Mechanisms of Fertilization

Concept 46.1: Both asexual and sexual
reproduction occur in the animal kingdom
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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
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Mechanisms of Asexual Reproduction
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Many invertebrates reproduce asexually by fission,
separation of a parent into two or more individuals of
about the same size
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Video: Hydra Budding
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In budding, new individuals arise from outgrowths of
existing ones
Fragmentation is breaking of the body into pieces, some
or all of which develop into adults
Fragmentation must be accompanied by regeneration,
regrowth of lost body parts
Parthenogenesis is the development of a new individual
from an unfertilized egg
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Figure 46.3-1
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Figure 46.3-2
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Figure 46.3-3
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Generation 3
Figure 46.3-4
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Generation 3
Generation 4
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Sexual reproduction results in genetic recombination,
which provides potential advantages
An increase in variation in offspring, providing an
increase in the reproductive success of parents in
changing environments
 An increase in the rate of adaptation
 A shuffling of genes and the elimination of harmful
genes from a population
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Reproductive Cycles
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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 seasonal temperature is often an important cue
in reproduction, climate change can decrease
reproductive success
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Some organisms can reproduce sexually or asexually,
depending on conditions
Several genera of fishes, amphibians, and lizards
reproduce only by a complex form of parthenogenesis
that involves the doubling of chromosomes after meiosis
Asexual whiptail lizards are descended from a sexual
species, and females still exhibit mating behaviors
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Variation in Patterns of Sexual
Reproduction
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For many animals, finding a partner for sexual
reproduction may be challenging
One solution is hermaphroditism, in which each
individual has male and female reproductive systems
Two hermaphrodites can mate, and some
hermaphrodites can self-fertilize
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Individuals of some species undergo sex reversals
Some species exhibit male to female reversal (for
example, certain oysters), while others exhibit female to
male reversal (for example, a coral reef fish)
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46.2 MECHANISMS OF
FERTILIZATION
Methods of Fertilization
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External
 Female
 Male
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eggs released into environment
fertilizes
Internal
 Sperm
is deposited in or near female reproductive tract
External
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Moist habitat
 Prevents
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Timing = crucial
More gametes
 Lower
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desiccation
zygote-survival rate
Spawning
 Release
of gametes in mass quantity
 Non-specific
fertilization
http://www.youtube.com/watch?v=wsaZ8I7akg
Mating Behavior
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“courtship”
 Allows
for mate choice
 Increases probability of successful fertilization
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Pheromones
 Chemicals
 Influence
physiology and behavior (e.g. attract)
Internal Fertilization
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Better zygote survival rate
 Eggs
sheltered
 Parental care (K selection)
 *often have additional adaptations
 Calcium/protein membranes
containing shells
Gamete Production
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Undifferentiated cells
 Simplest
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technique
Gonads
 Organs
that produce gametes
Delivery
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Males
 Testes
– organ in which sperm develops
 Seminal
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vesicles - storage
Females
 Ovaries
 Uterus
– develop eggs
– receives eggs
 Spermathecae
– sacs in which sperm can be stored
 Cloaca – one opening (digestive, excretory, reproductive)
Mechanisms that thwart or promote fertilization
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Male insects
 Transfer
secretions that make female less receptive to
courtship
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(abusive insect boyfriend)
http://www.youtube.com/watch?v=m2H-uTg51_c
46.3:
REPRODUCTIV
E ORGANS
PRODUCE
AND
TRANSPORT
GAMETES
Rachel Sylvia
Mr. Reis
AP Biology
8 April 2013
Female Reproductive Anatomy:
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External reproductive structures = clitoris and labia
(2 sets)
Internal reproductive structures = gonads (produce
eggs and hormones) and a system of ducts and
chambers which receive and carry gametes and
house the embryo and fetus
Ovaries :D
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Female gonads held in place by ligaments
Outer layer is packed with follicles each consisting
of am oocyte (partially developed egg surrounded
by support cells)
The surrounding cells protect and nourish during
formation and development of the egg
FUN FACT!
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SO…..You know ovulation? WELL… during a
*typical* 4- week menstrual cycle a single follicle
matures and dumps its egg which is OVULATION!
After ovulation the follicle tissue grows in the ovary
making a mass called the corpus luteum (yellow
body) which secretes hormones which help maintain
uterine lining during pregnancy
The corpus luteum degenerates and a new follicle
mautures in the next cyle if the egg Is not fertilized
Oviducts and Uterus
Vagina and Vulva
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The vagina is a muscular but elastic chamber that
is the site for instertion of the penis and
deposition of sperm during copulation
Also serves as a birth canal and opens to the
outside at the vulva (all the external genitalia)
Labia majora protects the rest of the vulva and
the vaginal opening of the urethra are in a cavity
bordered by tiny skinfolds known as the labia
minora
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Thin tissue called the hymen covers the
vaginal opening until sexual intercourse or
vigorous physical activity breaks it… gross
The clitoris is made of erectile tissue
supporting a glans (head) covered by a
hood of skin (prepuce)
The clitoris, labia minora and vagina all
engorge with blood during sexual arousal
(basically the female version of… yeah)
Mammary Glands
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Mammary glands are in
both sexes but only
produce milk in girls
Small sacs secrete milk
which drain into ducts
which open up at the
nipple
Breasts contain connective
and adipose tissue as well!
Man breasts are small
Male reproductive anatomy!
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Testes = male gonads which produce sperm
in coiled tubes called seminiferous tubules
Leydig cells produce testosterone
Testes have to be cooler than normal body
temperature to produce sperm in mammals..
Which is TOTALLY why they’re on the outside
of a dude!
The scrotum makes sure that the testis are at
a lower temp than the rest of the body
FUN FACT! Some mammals whose body
temperature is low enough to allow sperm
maturation such as whales and elephants
retain testes in the abdominal cavity
Accessory glands:
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1) seminal vesicles (yellowish, thick fluid)
2) prostate gland (milky, thin fluid)
3) bulbourethral glands (clear and
mucusy fluid)
Produce secretions which combine with
sperm to form semen
ATTENTION!
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BULBOURETHRAL FLUID
ALSO CARRIES SOME
SPERM RELEASED BEFORE
EJACULATION WHICH IS
WHY IT’S A BAD IDEA TO
GO FOR THE
WITHDRAWAL METHOD
OF BIRTH CONTROL,
FORMERLY CALLED
COITUS INTERRUPTUS
CAUSE SPERM CAN STILL
GET UP IN YO’ BODY.
Penis.
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The penis contains the urethra and 3 cylinders of
spongy erectile tissue which fills with blood from the
arteries
Which results in erection so that the penis can be
inserted into the vagina
Alcohol, some drugs, emotional issues, and again can
cause erectile dysfunction
The penis shaft is covered by skin , the head is covered
by thin skin so it is more sensitive, and the glans is
covered by prepuce or foreskin which is removed
through circumcision
Gametogenesis
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Gametogenesis = production of gametes
Spermatogenesis = formation and development of
sperm
It takes 7 weeks for one sperm to be created start
to finish! Oogenesis = development of mature
oocytes (eggs)
Immature eggs are formed but don’t mature until
yeeeeears later
Concept 46.5: In placental mammals, an
embryo develops fully within the mother’s
uterus
Kind of like…
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Conception, Embryonic Development, and
Birth
• An egg develops into an embryo in a series of
predictable events
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Conception, fertilization of an egg by a sperm, occurs in
the oviduct
The resulting zygote begins to divide by mitosis in a
process called cleavage
Division of cells gives rise to a blastocyst, a ball of cells
with a central cavity
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Figure 46.15
3
Cleavage
4
Cleavage
continues
5
Implantation
Ovary
2
Fertilization
Uterus
1
Ovulation
(a) From ovulation to implantation
Endometrium
Endometrium
Inner cell
mass
Cavity
Blastocyst
(b) Implantation of blastocyst
Trophoblast
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The embryo releases human chorionic
gonadotropin (hCG), which prevents
menstruation
Pregnancy/gestation- condition of
carrying one or more embryos in the
uterus
Body size + maturity of young at birth =
duration of pregnancy
Chromosomal or developmental
abnormalities can spontaneously
terminate pregnancies
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First Trimester
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Human gestation can be divided into three trimesters of
about three months each
The first trimester is the time of most radical change for
both the mother and the embryo
During implantation, the endometrium grows over the
blastocyst
(a) 5 weeks
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(b) 14 weeks
(c) 20 weeks
• During its first 2 to 4 weeks, the embryo obtains
nutrients directly from the endometrium
Maternal
arteries
Placenta
Umbilical
cord
Maternal
veins
Maternal
portion of
placenta
Chorionic
villus,
containing
fetal
capillaries
Fetal
portion of
placenta
(chorion)
Maternal
blood pool
Uterus
Fetal arteriole
Fetal venule
Umbilical cord
•
Umbilical
arteries
Umbilical vein
Outer layer of the blastocyst, called the trophoblast, mingles with the endometrium and
eventually forms the placenta
• The first trimester is the main period of organogenesis,
development of the body organs
• All the major structures are present by 8 weeks, and the
embryo is called a fetus
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Splitting of the embryo during the first month of
development results in genetically identical twins
Release and fertilization of two eggs result in fraternal
and genetically distinct twins
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Changes occur in the mother
Mucus plug to protect against infection
 Growth of the placenta and uterus
 Cessation of ovulation and the menstrual
cycle
 Breast enlargement
 Nausea is also very common
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Hormones cause changes
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Progesterone- hormone that maintains the
pregnancy (prevents menstruation)
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Second Trimester
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During the second trimester
The fetus grows and is very active
 The mother may feel fetal movements
 The uterus grows enough for the pregnancy to become
obvious
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Third Trimester
• During the third trimester, the fetus grows and fills the
space within the embryonic membranes
• A complex interplay of local regulators and hormones
induces and regulates labor, the process by which
childbirth occurs
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Figure 46.18
from
ovaries
Oxytocin

from fetus
and mother’s
posterior pituitary
Activates oxytocin
receptors on uterus
Stimulates uterus
to contract
Stimulates
placenta to make
Prostaglandins
Stimulate more
contractions
of uterus
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Positive feedback
Estradiol
Three Stages of Labor
Placenta
Umbilical cord
Uterus
Cervix
1 Dilation of the cervix
•
Delivery of the baby and
placenta is brought about by a
series of strong, rhythmic
uterine contractions
2 Expulsion: delivery of the infant
Uterus
Placenta
(detaching)
Umbilical cord
3 Delivery of the placenta
Maternal Immune Tolerance of the Embryo
and Fetus
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A woman’s acceptance of her “foreign” offspring is not
fully understood
It may be due to suppression of the immune response in
her uterus
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Contraception and Abortion
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Contraception, the deliberate prevention of pregnancy,
can be achieved in a number of ways
Contraceptive methods fall into three categories
Preventing release of eggs and sperm
 Keeping sperm and egg apart
 Preventing implantation of an embryo
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Figure 46.20
Method
A condom fits
over the penis
Female
Male
Event
Production
of sperm
Event
Production of
primary oocytes
Vasectomy
Oocyte
Sperm transport
development
down male
and ovulation
duct system
Abstinence
Condom
Coitus
interruptus
(very high
failure rate)
Method
Combination
birth control
pill (or injection,
patch, or
vaginal ring)
Abstinence
Female condom
Sperm
deposited
in vagina
Capture of the
oocyte by the
oviduct
Tubal ligation
Sperm
movement
through female
reproductive
tract
Transport
of oocyte in
oviduct
Spermicides;
diaphragm;
progestin alone
(as minipill
or injection)
Meeting of sperm and oocyte
in oviduct
Union of sperm and egg
Implantation of blastocyst
in endometrium
Morning-after
pill; intrauterine
device (IUD)
Detecting Disorders During Pregnancy
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Amniocentesis and chorionic villus
sampling are invasive techniques
in which amniotic fluid or fetal
cells are obtained for genetic
analysis
Noninvasive procedures usually
use ultrasound imaging to detect
fetal condition
Genetic testing of the fetus poses
ethical questions and can present
parents with difficult decisions
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Treating Infertility
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Modern technology can provide infertile couples with assisted reproductive technologies
In vitro fertilization (IVF) mixes eggs with sperm in culture dishes and returns the embryo to
the uterus at the 8-cell stage
Sperm are injected directly into an egg in a type of IVF called intracytoplasmic sperm
injection (ICSI)
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