Mendelian Crosses

Project #1477 on iSENSEProject.org

Students will predict outcomes of three Mendelian crosses in a species using Punnett Squares.  The first cross is between parents having only dominant alleles (homozygous dominant).  The second cross is one parent with only dominant alleles (homozygous dominant) and the other parent having one dominant and one recessive allele (heterozygous).  The third cross is between two parents each having one dominant and one recessive allele (heterozygous).  Students model the process using two different colored marbles, one representing the dominant allele (green) and the other the recessive allele (white).  Students compare predictions of Punnett Squares and actual outcomes, which will be displayed in bar and pie graphs.

Source:  Prentice Hall Science Explorer Cells and Heredity, Copyright 2007 by Pearson Education, Inc., publishing as Pearson Prentice Hall, Boston, Massachusetts 02116, pages 90 to 91.

Data used for this project completed by Marjorie Pine

Student Notes:

1.  You will be given two bags and six marbles, 3 each of two different colors.

2.  Decide which color will represent the dominant allele and which will be the recessive allele.

3.  Mark one bag #1 Female and the other bag #2 Male.

4.  Put two dominant marbles in one bag and two recessive marbles in the other bag.

5.  You will select one marble from each bag and write down the outcome of alleles.  This will be done 10 times.

6.  Create a data table to take down your data.

7. When you have completed this 10 times, change the bag with the recessive marbles to one recessive and one dominant marble.  Repeat Step 5 with the current bags.

8.  When you have completed Step 7, remove one dominant marble from the homozygous parent bag.  Replace it with a recessive bag.  You should have two heterozygous parents.  Repeat Step 5 with the current bags.

9.  Create Punnett Squares for each of the scenarios described.

10.  Use the instructions included to input your data into iSense project #1477

Questions

1.  How do your group's results compare to the expected outcome from the Punnett Squares?

2.  What happens to the comparison as other group's data is combined with yours?

3.  Why do you think this happens?