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Reproduction &
Development
Asexual & Sexual Reproduction
• Sexual reproduction produces offspring that are
genetically different from their parents.
• Asexual reproduction produces offspring
genetically identical to their parent.
• Examples:
1. Binary Fission
2. Budding
3. Spore Production
4. Fragmentation
5. Parthenogenesis
Modes of Reproduction
Asexual Reproduction
• One parent cell divides by mitosis to
produce 2 identical cells that are
clones of the parent
Types of Asexual Reproduction
1. Budding - an outgrowth on the parent organism
that develops into a new organism
that eventually separates from the
parent.
• Example-yeast and hydra
http://www.youtube.com/watch?v=489CSop00sY
2. Binary fission –DNA is copied through mitosis,
causing the original parent cell to split into
two smaller, genetically identical cells.
Example-bacteria
http://www.youtube.com/watch?v=D
Y9DNWcqxI4
3. Spore production - spores are produced by
mitosis and are released from the original
parent cell for dispersal.
• Example – Fungi (Rhizopus stolonifera)
http://bcs.whfreeman.com
/thelifewire8e/content/cat
_010/30040.html
4. Fragmentation – when a piece of the parent
organism breaks off and is dispersed. Each
section is able to form a new organism.
• Example - House plants formed from cuttings
Planaria flatworm
5. Parthenogenesis – when offspring are
produced from unfertilized eggs
• Example - some insects, such as the Oleander aphid
Sexual Reproduction
• In sexual reproduction new individuals are
produced by the fusion of haploid gametes
to form a diploid zygote.
• Sexual reproduction offers the benefit of
generating genetic variation among
offspring, which enhances the chances of
the population's survival.
Sexual Reproduction in Angiosperms
Life Cycle of Flowering Plants
1. Pollination
– Pollen is transferred from the anther to the
stigma
– Two types:
i. Self-pollination: occurs within the same
flower, or between flowers on the same plant
ii. Cross-pollination: Occurs between flowers on
different plants
2. Fertilization
– Pollen tube grows down through the style to deliver
sperm nucleus to the egg
– Egg and sperm unite to form a zygote
3. Seed Development
– Zygote grows and develops into an embryo plant
– Ovule wall thickens to become a seed coat
– Seed also contains stored food for the developing
embryo
4. Fruit Development
– Ovary tissue develops to enclose the seeds
– This is called the fruit (ex: apple, tomato, green
pepper
– Aids in seed dispersal
http://www.youtube.com/watch?v=RuYrFwDuYn0
What is found in a pollen grain?
1. A generative nucleus which divides to produce
two sperm nuclei
2. A tube nucleus which causes the pollen tube to
grow
What is found in an ovule?
• The ovule contains:
1. One Egg
2. Two polar bodies
What is double fertilization?
• When the pollen tube enters an ovule:
– one sperm nucleus fuses with an egg to form
the zygote (2n)
– the other combines with two polar nuclei to
form the endosperm (3n) - a food reserve
• http://www.youtube.com/watch?v=Gq8NWh98wQs
Monocots vs. Dicots
• Some angiosperms are monocots (one storage
structure in the seed)
– Others are dicots (two storage structures in the seed)
– monocot seeds store most of their food in the
endosperm
– Ex: corn
• dicot seeds store most of their food in the
cotyledons (seed leaves)
– Ex: beans
http://www.youtube.com/watch?v=gI2RxzAT-ww
Male Reproductive System
• The male gonad is the TESTES
• Testes produce SPERM and the hormones
TESTOSTERONE and INHIBIN
• The testes are located in the SCROTUM
– Sac outside the body cavity
– Temperature in scrotum is about 1.5oC cooler
than that of the abdominal cavity.
– Necessary so that sperm will develop properly
Review:
Structure
Function
Penis
Transfers sperm to the female
Testes
Make sperm (in seminiferous tubules) and
testosterone
Scrotum
Keeps testes at a lower body temp – outside
the body
Urethra
Carries semen and urine through the penis to
the outside
Cowper’s Gland,
Prostate Gland,
Seminal Vesicles
Epididymis
Secrete fluids into the urethra to nourish and
protect the sperm
Vas Deferens
Tube that leads sperm from the epididymis to
the urethra
Stores immature sperm for 18 hours until
they mature
• The path of the sperm from the inside to the
outside of the male:
TESTES (Seminiferous tubules)
EPIDIDYMIS
VAS DEFERENS
URETHRA
PENIS
OUTSIDE THE BODY
• Before ejaculation, the URETHRA blocks the
opening from the urinary bladder
Spermatogenesis
Male Sex Hormones
1. Follicle Stimulating Hormone (FSH)
• produced by the anterior pituitary gland
• stimulates the testes to produce sperm and the
hormone inhibin
2. Luteinizing Hormone (LH)
• produced by the anterior pituitary gland
• stimulates the testes to produce male sex
hormones (ex: Testosterone)
* FSH and LH are called gonadotropic hormones*
3. Testosterone - male sex hormone
• produced by interstitial cells of the testes
• causes the development of secondary sex
characteristics (hair growth, deepening of
voice, etc)
4. Inhibin
• produced by the seminiferous tubules of the
testes
• acts as a negative feedback signal for the
hypothalamus to regulate sperm production.
Female Reproductive System
• The female gonads are the OVARIES
• Located in the lower abdominal cavity
• Ovaries produce eggs (ova) and the hormones
ESTROGEN and PROGESTERONE
• Estrogen is the hormone responsible for
secondary sex characteristics (breasts, pelvis,
fat, menstruation)
Review
• The path of eggs from the inside of the female to
the outside of the female:
OVARY
OVIDUCT
UTERUS
CERVIX
VAGINA
OUTSIDE
• When an egg matures, the FOLLICLE (egg sac)
around it ruptures and the egg is released from
the OVARY (ovulation)
Structure
Function
Ovaries
Makes eggs and secretes estrogen
Oviduct
Tube lined with cilia for egg passage. Fertilization
(Fallopian Tube) occurs here.
Uterus
(Womb)
Thick, muscular and pear-shaped fertilized egg
develops here
Cervix
Narrow opening to the uterus. It expands during
childbirth
Leads to the outside of the body. Sperm are
deposited here. Baby and menstrual tissue exit
here.
Vagina
(Birth Canal)
Oogenesis
What is the Menstrual Cycle?
1. The maturation of an egg
2. The preparation of the uterus (womb) for pregnancy
• It begins at PUBERTY and stops during PREGNANCY
(temporarily) and MENOPAUSE (permanently)
• Ovulation (egg-releasing) occurs approximately midway
through the cycle
• If pregnancy does not occur, the UTERINE LINING
breaks down and is discharged…this is menstruation
http://www.sumanasinc.com/webcontent/animations/content/ovarianuterine.html
Stages of the Menstrual Cycle
1. Follicle Stage (lasts about 10 days)
• FSH produced by the PITUITARY GLAND
stimulates the growth of the FOLLICLE in the
ovary.
• The growing follicle produces ESTROGEN
– causes the wall of the UTERUS to grow and
thicken.
2. Ovulation (lasts 1 day)
• As ESTROGEN level increases, production of
FSH decreases
• Pituitary INCREASES its production of LH.
• This sudden INCREASE of LH causes
OVULATION
– Follicle bursts and an EGG is released
3. Corpus Luteum (lasts about 14 days)
• LH causes the ruptured FOLLICLE to turn into
the CORPUS LUTEUM or “yellow body”.
• The corpus luteum begins to produce the
hormone PROGESTERONE
– maintains the thick wall of the UTERUS.
– of ten called the “HORMONE of PREGNANCY”
4. Menstruation (lasts about 4 days)
– also called the Flow Stag
– Beginning of new cycle
• If FERTILIZATION does NOT occur:
– secretion of LH decreases
– UTERINE LINING breaks down.
– Blood and tissue pass out of the uterus through the
vagina
– This is called the woman’s PERIOD or
MENSTRUATION
Review:
http://www.youtube.com/watch?v=W
GJsrGmWeKE&safety_mode=true&pe
rsist_safety_mode=1&safe=active
Fertilization, Development
and Birth
Review: Male Reproductive Structures and Glands
Review: Female Reproductive Structures
Fertilization and Pregnancy
• Fertilization
– The union of egg and sperm
– Occurs in the Fallopian tube
• Pregnancy
– Occurs 6-7 days after fertilization
– Fertilized egg (zygote) divides by mitosis and moves
down into the uterus
– Young embryo becomes implanted in the
endometrium (inner lining of the uterus)
http://www.youtube.com/watch?v=BFrVmDgh4v4
Fertilization
OVIDUCT
UTERUS
EGG
CERVIX
VAGINA
OVARY
FOLLICLE
SPERM
Stages of Embryonic Development
•
•
•
•
•
•
•
•
Fertilization
Cleavage
Implantation of Blastocyst
Gastrulation
Neurula
Embryo
Fetus
Birth
Early embryological development:
1. Cleavage
– series of mitotic cell divisions in which zygote
becomes a mass of cells called the morula
– No growth occurs
2. Implantation of Blastocyst (or blastula)
– A hollow fluid-filled cavity develops inside the
morula
– Implantation occurs at this stage
Structure of Blastocyst
• Blastocoel – central cavity
(trophoblast)
• Trophoblast – outer layer;
forms part of the placenta
• Inner cell mass – becomes
the embryo
blastocoel
Inner cell mass
3. Gastrulation
– Cells of the trophoblast migrate inward to form 3
cell layers or germ layers
– The embryo is now called a gastrula
– Differentiation - the process in which the three
cell layers of the gastrula develop into different
parts of the body
• Ectoderm – will become skin and nervous system
• Endoderm – will become respiratory and digestive
systems
• Mesoderm – will become the muscles , circulatory
system, and other body systems
– (See Fig. 15.14 page 508)
4. Neurula
 Development of the nervous
system begins
 Cells of the ectoderm form
neural ridges, which fold
together to form a hollow
neural tube
 Neural tube becomes the
spinal cord
 anterior end becomes the brain
Early
development
How twins form
 Fraternal twins
 Develop from separate fertilizations
 Two different placentas develop
 Twins are not genetically identical
 Identical twins
 Develop from a single fertilized egg
 Early embryo splits into two (or more )
 Each develops into a separate embryo
 Genetically identical (clones)
 Usually share one placenta
• Conjoined twins
What happens during implantation?
• Occurs about 7 days after ovulation
• Blastocyst attaches itself to endometrium in
the uterus
• Trophoblast begins to secrete human
chorionic gonadotropin (HCG)
– Prevents corpus luteum from breaking down
– Can be detected in woman’s urine
• Basis of pregnancy test kits
Embryonic Membranes
• These membranes are not part of the embryo,
but support, nourish, and protect it.
• The embryonic membranes are:
1.
2.
3.
4.
Amnion (amniotic sac)
Chorion
Yolk
Allantois
1. Amnion (amniotic sac)
• a fluid-filled sac which surrounds the embryo
• develops from the trophoblast
• acts as a shock absorber and protects the
embryo.
• During birth, when the amniotic sac ruptures,
the fluid passes out of the vagina.
– This is known as the “water breaking”
2. Chorion
• develops from the trophoblast.
• located outside (surrounding) the amnion.
• has finger-like projections called chorionic villi
– villi connect with the endometrium of the uterus
– Chorionic villi and endometrium form the placenta
3. Yolk
– a membrane containing the food supply (as in the
yolk of a chicken egg). The yolk forms part of the
umbilical cord.
4. Allantois
– a membrane that collects wastes from the embryo
– this also becomes part of the umbilical cord.
What is the umbilical cord?
• a cord of tissue and blood
vessels which connects the
embryo to the placenta.
• contains umbilical arteries
carrying blood from the
embryo to the placenta, and
veins returning blood to the
embryo
What is the Placenta?
• Tissue through which exchange takes place
between mother and embryo
• Formed from endometrial tissue and embryonic
tissue
• Mother’s and embryo’s blood capillaries are very
close, but not directly connected, in the placenta.
• Materials (O2, food, wastes) pass from mother to
embryo, and vice versa, by diffusion.
• Produces estrogen and progesterone to inhibit the
release of FSH and LH.
– No ovulation or menstruation occurs during pregnancy.
The Placenta
What are Teratogens?
• Any substances and other factors which can
negatively affect the developing embryo.
• Examples:
1)alcohol
2) chemicals in cigarette smoke
3) prescription drugs (ex: thalidomide )
4) radiation.
• Exposure to these can cause defects such as physical
abnormalities,
– Ex: fetal alcohol syndrome, Down’s syndrome.
Effects of Teratogens
• FAS (Fetal Alcohol
Syndrome)
– mild to moderate mental
retardation
– behavior problems.
•Thalidomide
- shortening and
deformity of limbs
Stages of Development
•
Over a period of 38 weeks, a tiny clump of identical
cells develop into a human being with fully formed
tissues and organs.
•
The 38 weeks are divided into three time periods
called trimesters. These are called the first,
second, and third trimesters. Each trimester lasts
about 3 months.
First Trimester (Weeks 1 - 12)
•
At the end of 3 weeks, the embryo is called a neurula. At this stage the embryo has
the beginnings of a nervous system.
•
At the end of 4 weeks, the limbs, eyes and spine begin to form.
•
At 8 to 9 weeks, the first bone cells begin to form. The organism is known as a fetus
at this stage.
•
At 12 weeks, all of the major organs have started to form including ; the liver,
stomach, brain, and heart. As well, a noticeable head and limbs have developed.
•
The fetus is only 100 mm long at the end of this stage.
Second Trimester (Weeks 13 - 24)
•
In this stage, the fetus develops an
audible heartbeat.
•
The skeleton begins to form.
•
The brain and the nervous system
develop further.
•
The limbs continue to develop.
•
At the end of 24 weeks, most of a
fetus organs have developed.
•
The fetus is 300 mm long after 24
weeks.
Third Trimester (Weeks 25 - 38)
•
In the third trimester, the fetus size
increases quickly.
•
The immune system develops.
•
The brain continues to grow and
develop.
•
The fetus opens its eyes at the end
of the eighth month.
•
At the end of 9 months, the fetus is
around 525 mm long and weighs
about 3.38 kg.
http://www.youtube.com/watch?v=Ba2BbzV8cQY&safety_mode=true&persist
_safety_mode=1&safe=active
Birth
1. Dilation
– Cervix dilates (opens up) to allow baby to pass
through
– Muscles of the uterus begin to contract (labor)
• Caused by oxytocin – released by pituitary gland in
positive feedback loop
– Amniotic sac breaks and fluid flows from the
vagina
2. Expulsion
– Powerful contractions push the baby into the birth
canal (vagina)
– Baby passes out of mother’s body, head first,
through the vagina
– Umbilical cord is clamped and cut
http://www.youtube.com/watch?v=Xath6kOf0NE&safety_mode=true&persist_saf
ety_mode=1&safe=active
– Breech birth
• if the baby comes out buttocks or feet first
• High-risk birth – baby may suffer oxygen deprivation
3. Placental
– Further contractions of the uterus expel the
placenta
– This is known as the “afterbirth”
Alternative to natural birth – Caesarean Section
– Incision is made in mother’s abdomen and uterus
to remove the baby
http://www.youtube.com/watch?v=xyN48VnRYUY&safety_
mode=true&persist_safety_mode=1&safe=active
Lactation
•
the formation and secretion of breast
milk from the new mother.
• Prolactin - hormone which controls
the production of milk in a pregnant
female
– Released after woman has given
birth
– Suckling by infant stimulates release
of milk from breasts
– Initially, the breasts secrete a thin,
yellowish fluid called colostrum, but
eventually they secrete milk for the
baby.
http://www.youtube.co
m/watch?v=DQjMn0c370&safety_mode
=true&persist_safety_m
ode=1&safe=active
Fetal diagnostic techniques
1. Amniocentesis
– sample of amniotic fluid is
taken.
– fetal cells can be used to
produce a karyotype photograph of the fetal
chromosomes
– can be used to identify
chromosomal disorders (ex:
Down’s syndrome)
2. Chorionic Villi Sampling
– cell sample taken from the chorion of the
embryo. Karyotype is produced to detect
chromosome
– can be performed earlier in pregnancy than
amniocentesis, but at greater risk to the embryo.
3. Fetoscopy
– Observation of the fetus
in the womb through a
special camera
(endoscope) inserted into
the woman’s abdomen.
– Used with other
procedures (eg. Taking
blood samples, draining
excess fluid, fetal surgery)
4. Ultrasound
– high frequency sound waves are directed at the womb
– echo patterns produce a grainy image of the fetus
– Can be used to study external features of the fetus
• (eg. Determining sex of fetus)