Fertilization involves the fusion of an egg and sperm cell to form a zygote, activating embryonic development. Cells then differentiate as stem cells become specialized through DNA expression and gene activity, taking on specific roles. Embryos across generations display similarities because they develop from a common ancestor, though differentiation increases specialization over time.

1. UNIT 4
REPRODUCTION &
CELLULAR DIVISION
Section 4
Fertilization, Differentiation, and
Embryology
Biology - DeFord

2. FERTILIZATION
 Fertilization is the fusion of the
haploid sperm cell nucleus
with the haploid egg cell
nucleus to produce a diploid
zygote (fertilized egg).
 The process of fertilization
activates the egg, triggering the
beginning of embryonic
development.
 The first of many challenges

3. CELL DIFFERENTIATION
 Multicellular organisms begin
as undifferentiated masses of
cells called stem cells.
 Variation in DNA expression
and gene activity determine
the differentiation of cells and
ultimately their specialization.
 Differentiation is the process by which cells become
specialized. During the development of an organism,
cells differentiate into many types of cells.

4. CELL DIFFERENTIATION
 All cells contain the same DNA so cells initially have the
potential to become any type of cell. When a cell becomes
specialized, only specific parts of DNA are activated; the
activated DNA determine the function and structure of a
cell.
 A differentiated cell has become, quite literally, different
from the embryonic cell that produced it, and specialized to
perform certain tasks, such as contraction, photosynthesis,
or protection.
 At some point the adult cell reaches the point at which

5. EMBRYOLOGY – COMMON ANCESTOR
 Look at generation I.
What similarities
exist?
 All these embryos
have so much in
common because
they all come from a
common ancestor.
 Look at generation
III. Which organism