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Biology II
Development
?
?
Muscle
Intestinal
Nerve
EGG
Blood
Development
• How do we go from an egg to an adult?
• How do cells of one type change or produce
cells of another type?
• How is a cell lineage constrained?
• How does the genetic code cause these
changes?
OUTLINE 2
II. Cell Differentiation
A. What do we know?
B. The developmental landscape model
C. Two hypotheses for how cells become differentiated
1. Nuclear alteration
2. Nuclear differentiation
D.
Experimental evidence
1. Seward’s totipotent carrots
2. Gurdon - nuclear transplantation in toads
Waddington’s Developmental Landscape
Undifferentiated cell
Differentiated
cells
muscle
lung
brain
skin
Nuclear Alteration
(progressive loss)
Which One?
Nuclear Differentiation
(differential expression)
Fig. 21.5
Seward’s carrot experiment
Fig. 21.6
Nuclear transplantation
2% successful
Fig. 21.6
Nuclear transplantation
Serial transfers of nucleus
17% successful
Issues related to totipotency
Stem cell research
Dolly and “mom”
Noah - an
endangered guar
Fig. 21.8
New York Times: November 21, 2007
“Scientists Bypass Need for Embryo to Get Stem Cells
Two teams of scientists reported yesterday that they had turned
human skin cells into what appear to be embryonic stem cells
without having to make or destroy an embryo — a feat that
could quell the ethical debate troubling the field. All they had to
do, the scientists said, was add four genes.”
Place DNA modified by
addition of four genes into
skin cells – appear to act
as stem cells.
But added genes are
cancer genes
Clonal reproduction is not an
evolutionary novel concept
Some plants and animals do so
naturally
Clonal reproduction in plants
…and animals
Chordata
Cnidaria
Echinodermata
Development
Nuclear Differentiation has been
supported by experimental evidence,
Nuclear Alteration has been rejected.
Development occurs because the
same genetic blueprint is expressed in
different ways in different cells and at
different times.
Development
In order to understand the process of
development, we must understand
what controls the expression of genes
(how genes are turned on and off).
OUTLINE 3
III. Control of Gene Expression in Prokaryotes
A. Regulatory proteins
B. The operon model
C. Examples
1. the lac operon (substrate induction)
2. the tryp operon (end product repression)
3. the lac operon (positive control)