This document provides an overview of animal reproduction and development. It discusses both asexual and sexual reproduction mechanisms in animals. For sexual reproduction, it describes the processes of gamete production, fertilization, and embryonic development. Fertilization can be external or internal. Embryonic development involves cleavage, gastrulation, and organogenesis. Amniotes develop in extraembryonic membranes within the mother. Young can be precocial or altricial at birth, depending on their stage of development.

1. UNIT 5:
ANIMAL
REPRODUCTION AND
DEVELOPMENT
Campbell & Reece, 2010:
Chapters 46, 47

2. INTRODUCTION
 Animal reproduction takes
many forms
 Animal form and function can
be viewed broadly as
adaptations contributing to
reproductive success.
 Both asexual and sexual
reproduction occur in the
animal kingdom.

3. Sexual reproduction
Is the creation of an offspring
by fusion
of a male gamete (sperm)
and female gamete (egg)
to form a zygote

4. Asexual reproduction
Is creation of offspring
without the fusion of egg and
sperm.

5. ASEXUAL
REPRODUCTION

6. Mechanisms of Asexual
Reproduction
Many invertebrates
reproduce asexually.
One of these is by the
process of fission.
FISSION: Is the separation of
a parent into two or more
individuals of about the
same size.
FISSION OF AN
AMOEBA

7. Fission of a sea anemone to producer
two daughter organisms

8. Second method: BUDDING
In budding, new individuals arise
from outgrowths of existing ones
BUDDING OF A
HYDRA

9. Third method: 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
FRAGMENTATION AND
REGENERATION OF SEA STARS

10.  Fourth method: Parthenogenesis
 Is the development of a new
individual from an unfertilized egg

11. SEXUAL
REPRODUCTION

12. Introduction to sexual
Reproduction in animals
Almost all eukaryotic species
reproduce sexually.
Sexual reproduction results in
genetic recombination –
variation within species.

13. Genetic recombination provides
potential advantages:
1. An increase in variation in offspring,
2. An increase in the reproductive
success of parents in changing
environments.
3. An increase in the rate of
adaptation.
4. Elimination of harmful genes from
a population.

14. REPRODUCTIVE
CYCLES AND
PATTERNS

15. REPRODUCTION CYCLES AND
PATTERNS
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

16. Animals may reproduce asexually or
sexually, or they may alternate these
methods.
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 behaviours.

17. Sexual behavior in
parthenogenetic lizards

18. 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-
fertilize.
C. elegans makes both sperm
and eggs and can reproduce
by self-fertilization.

19. 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)

20. HOW DO
ORGANISMS
ENSURE THE
SURVIVAL OF
THEIR
OFFSPRING?

21. Ensuring the Survival of Offspring
All species produce more
offspring than the environment
can handle.
The proportion that survives is
small.
Species with external fertilization
produce more gametes than
species with internal fertilization.

22. 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
protective layers.
Other animals retain the embryo,
which develops inside the female.
In many animals, parental care helps
ensure survival of offspring.

23.  AMNIOTIC EGG OF A CHICKEN

24.  PARENTAL CARE OF AN INVERTEBRATE

25. GAMETE
PRODUCTION
AND DELIVERY

26. 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
undifferentiated tissue.

27. GONADS: MALE – TESTIS AND
FEMALE - OVARIES

28. Complex systems contain many
sets of:
 accessory tubes
 and glands that
carry
nourish,
and protect gametes and
developing embryos.

29. Some organisms have a cloaca:
is a common opening between
the external environment and the
digestive, excretory, and
reproductive systems
Common in non-mammalian
vertebrates;
Mammals usually have a
separate opening to the digestive
tract.

30. CLOACA OF A LIZARD

31. Monogamy is relatively rare
among animals.
Males and/or females which
have mechanisms to decrease
the chance of their mate mating
with another individual.

32. COURTSHIP
BEHAVIOUR
Courtship, in
animals –
behaviour that
results in mating and
eventual
reproduction

33. Courtship behaviours can
include:
special calls,
postures, and
movements,
special plumage,
bright colours or
other ornamentation

34. EXAMPLES
The 'dancing' done by male
birds of paradise.

36. Method of
reproduction in
which eggs are
laid and
embryos
develop

37. Three Methods of reproduction in
which eggs are laid and embryos
develop
Ovipary
Ovovivipary
Vivipary

38. OVIPARYOUS ORGANISMS
Reproduction in which eggs are laid
and embryos develop outside the
mother's body.
Each egg eventually hatching into a
young animal.
Little or no development occurs within
the mother's body.
Most invertebrates and many
vertebrates reproduce in this way.

39. Ovoviviparous:
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
(umbilical cord),
as certain reptiles, fishes, sharks,
insects.

40. VIVIPAROUS
Where the embryo develops
within the uterus.
and is nourished through a
yolk sac placenta from the
mother’s blood.
Young are born alive.
 most mammals and some
reptiles and fishes.

42. OVOVIVIPAROUS

43. ANIMAL
DEVELOPMENT

44. Introduction to animal development
The question of how a zygote becomes
an animal?
The first step is cell division (mitosis)
Second step: Cell differentiation (Is the
specialization of cells in structure and
function)
Third step: Morphogenesis (Is the
process by which an animal takes
shape.)

45. Fertilization

46. Fertilization
Fertilization depends on
mechanisms that bring together
sperm and eggs of the same
species.
All fertilization requires:
 critical timing,
mediated by:
 environmental cues,
 pheromones, and/or
 courtship behaviour.

47. Fertilization
Two types of fertilizations:
 External fertilization
 Internal fertilization

48. External Fertilization
In external fertilization,
eggs shed by the female
are fertilized by sperm of male
in the external environment.

49. Internal Fertilization
In internal fertilization,
sperm are deposited in or near the
female reproductive tract,
and fertilization occurs within the
tract

50. Internal Fertilization
Internal fertilization requires:
 behavioural interactions and
 compatible copulatory organs.
MALE
COPULATORY
ORGANS

51. PROCESS OF FERTILIZATION
Fertilization brings the haploid nuclei
of sperm and egg together, forming a
diploid zygote.
The sperm’s contact with the egg’s
surface initiates metabolic reactions
in the egg that trigger the onset of
embryonic development.
Metabolic reactions:
Acrosomal reaction
Cortical reaction

52. ACROSOMAL REACTION
Triggered when the sperm meets
the egg.
The acrosome, at the tip of the
sperm releases hydrolytic enzymes
that digest material surrounding the
egg.
Gamete contact depolarizes the
egg cell membrane and sets up a
fast block to polyspermy.

53. Sperm contacts egg

54. Acrosome releases
hydrolytic enzymes –
digest egg jelly coat

55. Actin filaments of acrosomal process
binds to the sperm binding receptors.

56. Plasma membranes of sperm
and egg fuses

57. Sperm releases haploid nucleus in egg cytoplasm
– fast block prevent polyspermy.

58. The Cortical Reaction
Initiated by the fusion of egg and
sperm.
It causes a rise in Ca2+.
This stimulates cortical granules to
release their contents outside the
egg.
Cause formation of a fertilization
envelope (functions as a slow
block to polyspermy.)

59. Rise of calcium in egg and
formation of fertilization envelope

60. 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.

61. EMBRYONIC DEVELOPMENT AFTER
FERTILIZATION
3 PROCESSES OCCURE IN AN EMBRYO
AFTER FERTILIZATION:
1.Cleavage
2.Gastrulation
3.Organogenesis

62. 1. CLEAVAGE
A period of rapid cell division
without growth.
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
blastocoel.

63. CELL DIVISION OF A FERTILIZED
EGG FORMING A BLASTULA

64. Two types of cleavage
Meroblastic cleavage, incomplete
division of the egg, occurs in species
with yolk-rich eggs, such as reptiles
and birds.
Holoblastic cleavage, complete
division of the egg, occurs in species
whose eggs have little or moderate
amounts of yolk, such as sea urchins
and frogs

65. 2. Gastrulation
Gastrulation –
rearranges the cells of a
blastula into a three-layered
embryo, called a gastrula,
which has a primitive gut
(archenteron)and opens in a
blastopore.

66. Three embryonic germ layers
of the gastrula
The ectoderm forms the outer
layer
The endoderm lines the
digestive tract.
The mesoderm partly fills the
space between the endoderm
and ectoderm.

67. GASTRULA OF A FROG

68. 3. ORGANOGENESIS
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
ectoderm.

69. ORGANOGENESIS
OF A FROG

70. The neural plate soon curves
inward, forming the neural tube
The neural tube will become
the central nervous system
(brain and spinal cord).

71. THE FATE OF THE 3 GERM
LAYERS
Fig. 47-14
ECTODERM MESODERM ENDODERM
Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
Epithelial lining of mouth
and anus
Cornea and lens of eye
Nervous system
Sensory receptors in
epidermis
Adrenal medulla
Tooth enamel
Epithelium of pineal and
pituitary glands
Notochord
Skeletal system
Muscular system
Muscular layer of
stomach and intestine
Excretory system
Circulatory and lymphatic
systems
Reproductive system
(except germ cells)
Dermis of skin
Lining of body cavity
Adrenal cortex
Epithelial lining of
digestive tract
Epithelial lining of
respiratory system
Lining of urethra, urinary
bladder, and reproductive
system
Liver
Pancreas
Thymus
Thyroid and parathyroid
glands

72. AMNIOTES

73. Developmental Adaptations of
Amniotes
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.

74. During amniote development, four
extraembryonic membranes form around
the embryo:
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.

75. EXTRAEMBRYONIC LAYERS OF BIRDS

76. PRECOCIAL
AND ALTRICIAL
DEVELOPMENT
PRECOCIAL YOUNG
ALTRICIAL YOUNG

77. 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
small litter.
Hares and many large grazing mammals
bear precocial offspring.
Rabbits, carnivores, and most rodents
bear altricial young.