Population Genetics
Introduction:  In studying evolution the genetic makeup of entire populations must be considered.  No organism makes a dramatic change in its appearance during a single lifetime in such a way that you could call it evolution.  Evolution is the change of the genetic makeup of a population over many generations.  This lab will introduce natural selection into several populations and observe the effects.

Case I: No selection

This population is 25% AA, 50%Aa, and 25% aa.  In other words, there is an equal number of each alelle.

Procedure:

1.  You will receive a card with your genotype.  You are going to pass on one of these alleles to your offspring.

2.  Randomly choose another member of the class to “mate” with.  It doesn’t have to be the opposite sex.

3.  If your genotype is heterozygous (Aa) flip a coin.  If it is heads, you pass on the dominant allele.  Tails, the recessive allele.

4.  Do this twice to produce two offspring.  Record the genotypes of your offspring as the F1 generation.

5.  Wait until everyone has finished producing the F1 generation.

6.  You now take on the genotype of one of the offspring.  Your partner takes the other.

7.  Now find another partner and begin the process again until you reach the F5 generation.
 
 
 

Your initial genotype: ________

  Child 1  Child 2

F1  _________  _________

F2  _________  _________

F3  _________  _________

F4  _________  _________

F5  _________  _________

Sum of entire population of F5.

AA  _________                 Aa  _________              aa  _________

Genotypic frequencies:

AA  _________%             Aa  _________%           aa  _________%

Allele frequencies:

A  _________%                  a  _________%

Based on these results, did this population change its allele frequencies significantly?
 
 
 
 


Case II: Natural selection- Recessive disadvantage

Often genetic disorders can be fatal.  Suppose you have a recessive disorder (i.e. cystic fibrosis), in nature you would not be able to survive long enough to mate and pass on your genes.

Procedure:

The procedure is identical to the last experiment with a few exceptions.

1.  You will again start with a card with your genotype.  The class will again have an equally distributed population.

2.  Repeat the mating procedure from the last trial.  The big exception is that every time the offspring is aa it dies.  You need to try again until you produce two offspring who survive.

3.  Continue the procedure until the F5 generation.

4.  Assume that if you start off aa, you are okay for this first generation.  However, you need to produce offspring that survive by not having the aa condition.

Your initial genotype: ________

  Child 1  Child 2

F1  _________  _________

F2  _________  _________

F3  _________  _________

F4  _________  _________

F5  _________  _________

Sum of entire population of F5.

AA  _________                 Aa  _________              aa  _________

Genotypic frequencies:

AA  _________%             Aa  _________%           aa  _________%

Allele frequencies:

A  _________%                  a  _________%

What happened to the frequency of the recessive allele?
 
 


Case III: Natural selection- Heterozygote advantage

In Western Africa, sickle cell anemia is a genetic disorder that can reduce the survival rate in harsh conditions.  However, being a carrier of the allele for the disorder can increase that person’s resistance to malaria significantly.  This means a the AA condition is disadvantaged for one reason and the aa condition is disadvantaged for another.

Procedure:

The procedure is again identical to the last experiment with another new exception.

1.  You will again start with a card with your genotype.  The class will again have an equally distributed population.

2.  Repeat the mating procedure from the last trial.  The new exception is that every time the offspring is AA or aa it dies.  You need to try again until you produce two offspring who survive.

3.  Continue the procedure until the F5 generation.

4.  Assume that if you start off AA or aa, you are okay for this first generation.  However, you need to produce offspring that survive by not having the aa condition.

Your initial genotype: ________

  Child 1  Child 2

F1  _________  _________

F2  _________  _________

F3  _________  _________

F4  _________  _________

F5  _________  _________

Sum of entire population of F5.

AA  _________                 Aa  _________              aa  _________

Genotypic frequencies:

AA  _________%             Aa  _________%           aa  _________%

Allele frequencies:

A  _________%                  a  _________%

What happened to the frequency of the heterozygous individuals?
 
 
 


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