Post on 16-Jan-2016
Biology II
Development
?
?
Muscle
Nerve Blood
Intestinal
EGG
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 alteration2. Nuclear differentiation
D. Experimental evidence
1. Seward’s totipotent carrots2. Gurdon - nuclear transplantation in toads
Waddington’s Developmental Landscape
brain skinmuscle lung
Undifferentiated cell
Differentiatedcells
Nuclear Alteration (progressive loss)
Nuclear Differentiation(differential expression)
Which One?
Fig. 21.5 Seward’s carrot experiment
Fig. 21.6Nuclear transplantation
2% successful
Fig. 21.6Nuclear transplantation
Serial transfers of nucleus
17% successful
Fig. 21.8
Dolly and “mom”
Stem cell research
Noah - an endangered guar
Issues related to totipotency
“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.”
New York Times: November 21, 2007
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
ChordataCnidaria
Echinodermata
…and animals
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)