# How Leopards get Their Spots Will Brennan - PowerPoint PPT Presentation

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## How Leopards get Their Spots Will Brennan

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### One was developed by James Murray, and the other was developed by David Young ... if AD - w*ID = 0 leave the central cell unchanged. Model in Action. Young's model ... – PowerPoint PPT presentation

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Title: How Leopards get Their Spots Will Brennan

1
How Leopards get Their SpotsWill Brennan
• How Zebras Get Their Stripes

2
Spots and Stripes
• Skin coloration is caused by melanin
• What is the cause of specific patterns such as
spots and stripes?

3
Modeling animals
• Spot and stripe arrangement are random and
distinct, yet share a definite pattern
• This led mathematicians to
• realize that there must be
• some way to model the
• phenomena

4
Models Emerge
• Two models emerge
• One was developed by James Murray, and the other
was developed by David Young
• Both models both incorporate the same elements
however reaction-diffusion

5
Young Model
• Youngs model is based off of cellular automata
modeling
• Young has 4 assumptions on his model
• There are two types of cells colored(D) and
uncolored(U)
• The colored cells secrete 2 morphagens an
inhibitor(I) and an activator(A)

6
Diffusion of Morphagens
• As the D cells release the A and I morphagens,
they diffuse throughout the environment
• Near the D cells, there is a higher concentration
of A, but this is inverse with its distance from D

7
Whats it all mean?
• Cell type is determined by the concentration of
the morphagens in its area
• If over a U cell, AI then the cell will switch
to a D and start producing morphagens
• Conversely, if over a D cell, IA, then it will
change to a U

8
How does this explain the patterns?
• if AD - wID 0 set the central cell to D,
• if AD - wID 0 leave the central cell
unchanged.

9
Model in Action
• Young's model
• The shape of the patterns can then be changed by
inputting different variables for the area of the
model

10
Murrays model
• Also based on reaction-diffusion, but
concentrated on the rate of diffusion as opposed
to concentration
• Also had two chemicals an inhibitor and an
activator working on the cells

11
Speed is of the essence
• The chemicals work at different speeds
• The activator is slower
• While the inhibitor is faster
• This disparity in speed allows the inhibitor to
surround the activator during diffusion, causing
a spot.

12
An Analogy
• Forest Fires mimic this same dynamic
• Fires burn first, but diffuse slowly.
• Firefighters respond, spraying untouched trees
surrounding the fire with anti-inflammatory
chemicals, containing the fire in Spots

13
Theory in action
• By changing the rate of diffusion then, the
pattern will be different.
• Murray also found as Young did that shape plays a
role in the development of the pattern

14
Spots vs Stripes
• Since spotted leopards and striped tigers are