EEB 461/561  Homework #1

Fun with genetic drift

This exercise allows YOU! to simulate genetic drift in a very simple way.

Requires:   
	¥ six pennies, six dimes (or six marbles of one color and six of another, 
	       or six paper slips  marked A and another six marked a, etc.) 
	¥  A cup, hat or some other container 

To start:

Place three of one item (pennies, paper slips marked A, etc.) and three
of the other (dimes, paper slips marked a, etc.) into the cup.   Let the
first item (the penny) represent allele A, and the second item (the dime) mark
 allele a.   Thus, you are starting with a population of six alleles, three of 
which are A (50%).

Blindly draw one item from the cup,  write down what is was, and replace it.  
Repeat this process six times to generate the next generation.  Note this is 
sampling with replacement.  Suppose n copies of allele A are drawn. 
If  n = 0 or 6, the population is fixed for allele a or A, respectively.  If 0 < n < 6, 
then form the next generation by placing n copies of allele A into the cup and 
6-n copies of allele a.  For example, if five dimes were drawn, then the next 
generation starts with five dimes and one penny.

Repeat this, writing down the allele frequencies each generation, until allele 
A is either lost or fixed.  Repeat the entire run three times.  Graph the three 
sample paths for these runs (the frequency of allele A over time).

Part two:  Now start with a single copy of allele A. Repeat the above sampling 
scheme until one allele becomes fixed, and repeat the trails until A is the 
allele that becomes fixed.  How many trails were required to fix A?

Bring this information to class on Tuesday and we will plot the entire class.