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sheep-fussyfemales

by Ed Hazzard (Submitted: 02/07/2005)

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Evolution: Sheep-fussyfemales
This is a model of a flock of sheep whose survival depends on eating grass. The babies inherit traits from their parents according to Mendelian genetics. One can watch the spread of a mutation and how it depends on selection pressure. There are two such pressures here: the energy sheep get from grass, and the fact that females will not breed with mutated sheep.

Here are are some explorations:
1. Picture yourself as a farmer with a large field of sheep. You start with an equal number of males (horns) and females (no horns). They live for six years. The sheep move around the field and eat grass, which grows back at a certain rate. The patch is green if there is grass there, and brown if there is no grass. In the model, the sheep move and eat during each year. They use up energy as they move, and they gain energy from eating grass. If their energy goes to zero, they die.

2. Once a year, from age 3 to age 6, each female mates with a randomly chosen male and gives birth to a baby. The baby inherits its TEETH trait from both its parents.

3. In this version, all of the sheep have standard teeth. There are two new
features, one a pressure in favor of the muation, and one opposing it:
a. An ADD MUTANTS button. When you hit this button, some blue sheep are added to the herd. Sheep pass their color gene on to their offspring.
b. A FUSSYFEMALES button. When you hit this button, females refuse to mate with blue (mutated) males.

4. If SELECTION? = ON, a blue sheep gets twice as much energy from grass as a regular sheep. If SELECTION? = OFF, the blue color has no effect on its eating or how likely it is to survive and have offspring.

5. Try the model with SELECTION? on or off, and FUSSYFEMALES? on or off. Run the model, add at least 15 mutants, and fill in the following table.

Condition What happens

SELECTION? = OFF
FUSSYFEMALES? = ON

SELECTION? = ON
FUSSYFEMALES? = OFF

SELECTION? = ON
FUSSYFEMALES? = ON

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