Fertilization involves the combining of haploid sets of chromosomes from two individuals into a zygote. This is followed by cleavage, where rapid cell division occurs. Then gastrulation takes place, where cells migrate to locations that will form organs and tissues. Finally, organogenesis occurs, where organ rudiments develop from the three germ layers.

1. Animal Development
Chapter 47
Keonna & Brianna

2. Fertilization, cleavage, Gastrulation,&
Organogenesis
 Main function of fertilization is the combining of haploid
sets of chromosomes from two individuals into a single
diploid cell, the Zygote.
 Acrosomal reaction- The discharge of hydrolytic enzymes that come
from a vesicle in the tip of the sperm, the acrosome, occurs when the
sperm approaches or touches the egg.
 Cortical reaction – Excocytosis of enzymes and other
macromolecules from cortical granules in the egg cytoplasm during
fertilization, leading to the formation of fertilization envelope.
 After fertilization is complete, rapid cell divison occurs.
This stage called cleavage, the cells carry out the S and M phases of
the cell cycle.

3. The acrosomal & cortical reactions during
sea urchin fertilization.

4. Fertilization, cleavage, Gastrulation,&
Organogenesis
 After cleavage, the rate of cell division slows down,
and undergo a process called gasturlation. This
process takes up locations that will later for organs
and tissues.

5. Fertilization, cleavage, Gastrulation,&
Organogenesis
 Organogenesis is the process in which organ
rudiments development from, the 3 germ layers after
gastrulation

6. Developmental
adaptations of amniotes Mammalian development
 Require aqueous environment for  Fertilization occurs in the oviduct,
development. then continues as it completes its
 Reptiles and mammals in eggs or journey to the uterus.
the uterus are surrounded by a  When embryonic cells separate ,
fluid within are called amniotes. causes twins
 Chorin, amnion, yolk sac, and the  Allantois in mammals is
allantois make up the “life-support incooperated in the umbilical cord.
system” for further embryonic  There it forms blood vessels that
development transport Oxygen/nutrients from
the placenta and gets rid of
harmful waste and carbon dioxide.

7. Morphogenesis in animals involves specific
changes in cell shape,position,and adhesion
 Changes of the cells usually involve the
reorganization of the cytoskeleton. Cytoskeleton
drives cell migration.
 Cell adhesion molecules- cell-surface molecule
that bonds to CAM’s on other cells results in
cell-to-cell attachments contribute contributing to
strong tissues attachments.
Credit: 8th edition biology: Cambell.Reece

8. Developmental Fate of Cells
 During early cleavage  Fate maps provide a
divisions have to territorial diagram of
differentiate themselves. embryonic development
 Initial differences result  Fate maps also trace the
from uneven distribution ancestry of each cell
of cytoplasmic  In many species that
determinants have cytoplasmic
 Induction - Interactions determinants only the
among embryonic cells zygote is totipotent
influence their fate by  Totipotent – capable of
changing gene turning into all the
expression different cell types in that
species

9. Developmental Fate of Cells
 Inductive signals play an  Two critical regions in a
important role in: limb bud have profound
 pattern formation – the effects on the limb’s
arrangement of organs and development
tissues  Apical Ectodermal Ridge – a
 Positional information – thickened area of the
tells a cell where it is in ectoderm at the tip of the
location to the animal’s bud. Removal of it prevent
body axes and determine growth of the limb
how the cells and its  Zone of Polarizing Activity - a
desendants will respond to block of mesodermal tissue
molecular signaling underneath the ectoderm
where the posterior side in
attached to the body. It is
neccesary for proper pattern
formation

10. Developmental Fate of Cells
 Hox genes play an  Mutation in the Hox
important role in the genes can cause cells
development of limbs. in the limb buds to react
 Research suggests that differently to the
pattern formation positional cues
requires cells to receive  Can cause
and interpret cues from polysyndactyly
the environment
 This tells cells where
they are in the
developing organ