Campbell & Reece, 2010:
Chapters 46, 47
Animal reproduction takes
Animal form and function can
be viewed broadly as
adaptations contributing to
Both asexual and sexual
reproduction occur in the
Is the creation of an offspring
of a male gamete (sperm)
and female gamete (egg)
to form a zygote
Is creation of offspring
without the fusion of egg and
Mechanisms of Asexual
One of these is by the
process of fission.
FISSION: Is the separation of
a parent into two or more
individuals of about the
FISSION OF AN
Fission of a sea anemone to producer
two daughter organisms
Second method: BUDDING
In budding, new individuals arise
from outgrowths of existing ones
BUDDING OF A
Third method: FRAGMENTATION
Is breaking of the body into pieces,
some or all of which develop into
Fragmentation must be accompanied
by regeneration - regrowth of lost
REGENERATION OF SEA STARS
Fourth method: Parthenogenesis
Is the development of a new
individual from an unfertilized egg
Introduction to sexual
Reproduction in animals
Almost all eukaryotic species
Sexual reproduction results in
genetic recombination –
variation within species.
Genetic recombination provides
1. An increase in variation in offspring,
2. An increase in the reproductive
success of parents in changing
3. An increase in the rate of
4. Elimination of harmful genes from
REPRODUCTION CYCLES AND
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
Animals may reproduce asexually or
sexually, or they may alternate these
Lizards reproduce only by a complex form
of parthenogenesis that involves the
doubling of chromosomes after
Asexual whiptail lizards are descended
from a sexual species, and females still
exhibit mating behaviours.
Sexual reproduction is a special
problem for organisms that
seldom encounter a mate.
One solution is hermaphroditism,
in which each individual has male
and female reproductive systems
Some hermaphrodites can self-
C. elegans makes both sperm
and eggs and can reproduce
Individuals of some species undergo
Some species exhibit male to
female reversal (for example,
while others exhibit female to male
reversal (for example, a coral reef
Ensuring the Survival of Offspring
All species produce more
offspring than the environment
The proportion that survives is
Species with external fertilization
produce more gametes than
species with internal fertilization.
Species with internal fertilization
provide greater protection of the
embryos and more parental care.
The embryos of some terrestrial animals
develop in amniote eggs with
Other animals retain the embryo,
which develops inside the female.
In many animals, parental care helps
ensure survival of offspring.
Gamete Production and Delivery
Sexually reproducing animals have
systems producing gametes.
These individuals have gonads -
organs producing gametes.
Male gonads : Testis
Female gonads: Ovaries
Some gametes form from
Complex systems contain many
and glands that
and protect gametes and
Some organisms have a cloaca:
is a common opening between
the external environment and the
digestive, excretory, and
Common in non-mammalian
Mammals usually have a
separate opening to the digestive
Monogamy is relatively rare
Males and/or females which
have mechanisms to decrease
the chance of their mate mating
with another individual.
results in mating and
Courtship behaviours can
bright colours or
The 'dancing' done by male
birds of paradise.
which eggs are
Three Methods of reproduction in
which eggs are laid and embryos
Reproduction in which eggs are laid
and embryos develop outside the
Each egg eventually hatching into a
Little or no development occurs within
the mother's body.
Most invertebrates and many
vertebrates reproduce in this way.
Animals produce eggs, but instead
of laying the eggs, the eggs develop
within the mother's body.
The young eat unfertilized eggs in
the womb for nourishment
The young are born alive
without placental attachment
as certain reptiles, fishes, sharks,
Where the embryo develops
within the uterus.
and is nourished through a
yolk sac placenta from the
Young are born alive.
most mammals and some
reptiles and fishes.
Introduction to animal development
The question of how a zygote becomes
The first step is cell division (mitosis)
Second step: Cell differentiation (Is the
specialization of cells in structure and
Third step: Morphogenesis (Is the
process by which an animal takes
Fertilization depends on
mechanisms that bring together
sperm and eggs of the same
All fertilization requires:
In external fertilization,
eggs shed by the female
are fertilized by sperm of male
in the external environment.
In internal fertilization,
sperm are deposited in or near the
female reproductive tract,
and fertilization occurs within the
Internal fertilization requires:
behavioural interactions and
compatible copulatory organs.
PROCESS OF FERTILIZATION
Fertilization brings the haploid nuclei
of sperm and egg together, forming a
The sperm’s contact with the egg’s
surface initiates metabolic reactions
in the egg that trigger the onset of
Triggered when the sperm meets
The acrosome, at the tip of the
sperm releases hydrolytic enzymes
that digest material surrounding the
Gamete contact depolarizes the
egg cell membrane and sets up a
fast block to polyspermy.
Sperm releases haploid nucleus in egg cytoplasm
– fast block prevent polyspermy.
The Cortical Reaction
Initiated by the fusion of egg and
It causes a rise in Ca2+.
This stimulates cortical granules to
release their contents outside the
Cause formation of a fertilization
envelope (functions as a slow
block to polyspermy.)
Rise of calcium in egg and
formation of fertilization envelope
Activation of the Egg
The sharp rise in Ca2+ in the egg’s
cytosol increases the rates of
cellular respiration and protein
synthesis by the egg cell.
Now the egg is said to be activated.
The sperm nucleus merges with the
egg nucleus to form a diploid
zygote and cell division begins.
EMBRYONIC DEVELOPMENT AFTER
3 PROCESSES OCCURE IN AN EMBRYO
A period of rapid cell division
This creates a hollow ball of cells
called a blastula.
The blastula consists of many
smaller cells called blastomeres
The hollow part of the blastula is
filled with fluid and called a
CELL DIVISION OF A FERTILIZED
EGG FORMING A BLASTULA
Two types of cleavage
Meroblastic cleavage, incomplete
division of the egg, occurs in species
with yolk-rich eggs, such as reptiles
Holoblastic cleavage, complete
division of the egg, occurs in species
whose eggs have little or moderate
amounts of yolk, such as sea urchins
rearranges the cells of a
blastula into a three-layered
embryo, called a gastrula,
which has a primitive gut
(archenteron)and opens in a
Three embryonic germ layers
of the gastrula
The ectoderm forms the outer
The endoderm lines the
The mesoderm partly fills the
space between the endoderm
During organogenesis, various
regions of the germ layers
develop into organs.
Early in vertebrate
organogenesis, the notochord
forms from mesoderm, and the
neural plate forms from
The neural plate soon curves
inward, forming the neural tube
The neural tube will become
the central nervous system
(brain and spinal cord).
THE FATE OF THE 3 GERM
ECTODERM MESODERM ENDODERM
Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
Epithelial lining of mouth
Cornea and lens of eye
Sensory receptors in
Epithelium of pineal and
Muscular layer of
stomach and intestine
Circulatory and lymphatic
(except germ cells)
Dermis of skin
Lining of body cavity
Epithelial lining of
Epithelial lining of
Lining of urethra, urinary
bladder, and reproductive
Thyroid and parathyroid
Developmental Adaptations of
Embryos of birds, other reptiles,
and mammals develop in a fluid-
filled sac in a shell or the uterus
Organisms with these adaptations
are called amniotes.
During amniote development, four
extraembryonic membranes form around
The chorion functions in gas exchange
The amnion encloses the amniotic fluid
The yolk sac encloses the yolk
The allantois disposes of waste products
and contributes to gas exchange.
At birth the young may be well-developed
and able to move about at once, this is
called precocial development.
If at birth the young are maybe blind,
hairless, and essentially helpless, it is
called altricial development.
In general, precocial young are born after
a relatively long gestation period and in a
Hares and many large grazing mammals
bear precocial offspring.
Rabbits, carnivores, and most rodents
bear altricial young.