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 through internal or external means, and embryonic development through cleavage, gastrulation and organogenesis. For embryonic development, it highlights adaptations in amniotes including extraembryonic membranes. Offspring can be precocial or altricial at birth depending on the level 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

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

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, 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 DEVELOPOvipary
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

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.