Biology II

Development

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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)