Fertilization & Development
• Fertilization occurs in the oviduct
• Sperm + Egg  Zygote
• Haploid +Haploid  Diploid
Formation of the Zygote
Once fertilization has occurred and the
genetic material has combined, cell
division begins.
Is it mitosis or meiosis?
Formation of the Zygote
Once fertilization has occurred and the
genetic material has combined, cell
division begins.
Is it mitosis or meiosis?
Mitosis
Formation of the Zygote
A special type of mitotic cell division called
cleavage occurs.
Formation of the Zygote
Cleavage results in
cells being formed
which become
progressively smaller.
Formation of the Zygote
Notice how the over
all size remains the
same while the
number of cells
increase.
Formation of the Zygote
Formation of the Zygote
Cleavage occurs
while the zygote is
moving through the
oviduct.
Formation of the Zygote
As the zygote develops it goes through
several specific phases.
These are the :
– Morula
– Blastula &
– Gastrula
Formation of the Zygote
The Morula is a solid
ball of cells.
This develops during
the first few days after
conception.
Formation of the Zygote
The Blastula is a
hollow ball of cells.
Formation of the Zygote
The Gastrula is
formed from the
blastula.
It establishes the
three embryonic
tissue layers.
Formation of the Zygote
The three layers are:
– Endoderm
– Mesoderm &
– Ectoderm
Formation of the Zygote
The ectoderm gives rise to the skin and
nervous system.
Formation of the Zygote
The ectoderm gives rise to the skin and
nervous system.
The mesoderm gives rise to the muscles,
bones, circulatory and excretory systems.
Formation of the Zygote
The ectoderm gives rise to the skin and
nervous system.
The mesoderm gives rise to the muscles,
bones, circulatory and excretory systems.
The Endoderm gives rise to the digestive
and respiratory systems.
Implantation
The Morula secrets a
hormone, HcG.
This maintains
Progesterone levels,
preventing
menstruation.
Implantation
HcG is detected early
and forms the basis
for the home
pregnancy test kits .
Implantation
Implantation occurs in
the endometrial lining
of the uterus.
This occurs by day 7.
Associated Structures
The umbilical cord
connects the embryo
to the placenta.
Associated Structures
The umbilical cord
connects the embryo
to the placenta.
In adults, its scar
forms the navel.
Associated Structures
The placenta is the
site of gas and
nutrient exchange
between the mother
and the fetus.
Associated Structures
The Amniotic Fluid is
the liquid that the
baby floats in.
It serves as a
cushion.
Multiple Births
Multiple births can occur two ways:
– The splitting of one fertilized egg that will give
rise to identical twins
Multiple Births
Multiple births can occur two ways:
– The splitting of one fertilized egg that will give
rise to identical twins
– Multiple eggs are fertilized giving rise to
fraternal twins (not identical)
Twins
In Vitro Fertilization
Types of Sexual Reproduction
The reproductive pattern shown by
mammals and marsupials involves internal
fertilization and internal development.
Types of Sexual Reproduction
The reproductive pattern shown by
mammals and marsupials involves internal
fertilization and internal development.
The number of off spring per pregnancy is
low but parental care is high.
Types of Sexual Reproduction
Types of Sexual Reproduction
The reproductive pattern shown by reptiles
and birds involves internal fertilization but
external development (egg)
The number of off spring is higher, and
parental care is variable.
Types of Sexual Reproduction
Types of Sexual Reproduction
The reproductive pattern shown by
amphibians and fish involves external
fertilization and external development
The number of off spring is much higher,
and parental care is usually lacking
Types of Sexual Reproduction
Types of Sexual Reproduction
Regardless of the
type of sexual
reproduction, the
development of the
embryo is similar.