Pea Plant Genetics

Project #1470 on iSENSEProject.org

http://isenseproject.org/projects/1470

Up to this point in our Genetics & Heredity Unit, students will have learned that organisms have 2 genes for each trait they possess (it is explained that this is not the case with ALL traits, but for our purposes, at this level, we use this to learn/understand how the traits are handed down from parent organisms to their offspring).  They have also learned that an organism receives half of their genes/chromosomes from each parent organism and that each time the organisms are "crossed" it is a random selection of which genes are passed on to the offspring from each parent.  They will also have learned how to show the results of a genetic cross using a Punnett Square so that they can see the probable outcomes of the genotypes and phenotypes of the offspring.  

A classic example of showing this phenomenon in genetics is through the use of the traits of pea plants (Gregor Mendel's studies).  Prior to using this project in iSense, I would have the students complete a Punnett Square crossing two parents with the genotypes of Tt and Tt for the trait of height in a pea plant.  The results would show the theoretical probabilities of getting each of the different genotypes of the offspring in a genetic cross between these two parents.

In this iSense project, I would do an activity where the students would have 4 cards - two representing the two genes of one parent and the other two representing the two genes of the other parent pea plant.  The students would put the the two pairs of cards in two separate bags and randomly pull one from each parent representing a cross between the two parents and a possible genotype of one of their offspring.  Each student (or pair of students) would do this ten times, tallying the number of times each different genotype (TT, Tt, or tt) comes up when crossing these two particular genotypes of the parent pea plants.  The parent genotypes used in this activity were Tt and Tt but this could be done with another combination of parent genotypes as well.  

Once the students see the results in bar graph and pie chart form they can compare these results to the probabilities of the Punnett Square.  With more and more data, we would expect to see the actual outcomes come close to the probable outcomes.  When crossing parents Tt X Tt in a Punnett Square, we would expect to see outcomes of 25% TT, 50% Tt and 25% tt.

NOTES:  

1.  iSENSE did not recognize lower vs. uppercase letters so the choices students were given for the gentoypes of the offspring were TallTall, TallShort, and ShortShort instead of TT, Tt and tt.

2.  The data entered is from the results of my own crossing of these two parents.  I ran the activity myself five times.

Directions for Students:

1.  Put the two gene (allele) cards for Parent Pea Plant 1 in one bag and the two gene cards for Parent Pea Plant 2 in another bag.

2.  Without looking, randomly select one gene (allele) from each bag to make a gene combination for the offspring.  Record this as a tally mark for this genotype on paper.

3.  Repeat this step for a total of 10 selections, tallying the number of each genotype you get.  

4.  When completed, enter the given Contributor Key into iSense project #1470 and enter the total number of each genotype you got in the data chart.  

5.  Use the data visualization (the bar and pie graphs) of the class results to answer the following guiding questions.

Guiding Questions:

1.  Which genotype showed up the most often in the class data for the offspring when crossing the the two parents of gentoypes Tt and Tt?

2.  Which genotype showed up the least often in the class data for the offspring when crossing these same parents?

3.  How did the actual outcomes (the class results) compare to the probabilities of getting each of the different genotypes as seen in the results of the Punnett Square when crossing these two parents?  Explain using data.