Teacher Version


Name: _______________________ Date: ___________________

A Horns Activity:  Taking Data:  Understanding how to take data that will generate ratios and statistics

GenScope File: HornsExperiment.gs
The Horns Experiment file is locked so that it cannot be modified by the students. If you should lose it and have to reproduce it, the genomes of the parents are as follows: Dolly: Hh; Ww, LL, tT; F-, A-, B-. Solly: Hh; Ww, ll, TT; FF, aa, BB. They are set to have their alleles and DNA observable but not alterable. The password for changing this setting is "dragon." Number of offspring (under "Pedigree Options") is set to 40.

1.       Start GenScope and open the Horns Experiment organism file.

Note that you may double click on the Horns Experiment file from the Finder - this will start GenScope and open the file. You can also start GenScope by double-clicking on the application program and then use the File, Open File menu selection to open the Horns Experiment file from within GenScope

2.      GenScope will come up with two dragons, a male and a female, in a pedigree window set to show the "Horns" trait. In other words, in this window, dragons with horns are open circles or squares (circles for females, squares for males) and hornless dragons are closed (black) circles and squares. (If you want to see what your dragons look like, use the magnifying glass.) Both of your dragons have horns, so the circle and the square are both open (white).


3.      Use the cross tool (it looks like a "multiplication sign") to breed your two dragons. This cross will result in a great big family of dragon children (offspring).

4.       Count how many of these have horns and how many don't, then enter your data below:

Number of horned offspring: _____________
Number of hornless offspring: _____________
Total number of offspring: _____________   On the surface this exercise is a simple case of producing offspring at the pedigree level. A large number of offspring are produced and the student counts the number of horned and hornless dragons.

Here is a chance for you to use a straightforward activity to drive home some interesting lessons. Since having horns is dominant to being hornless, one would expect two heterozygotes (Hh) to produce offspring in a ratio of 1 HH: 2 Hh: 1 hh, or 3 horned to 1 hornless. The students should count up the various types of dragons (looking at only their phenotypes) and enter the numbers in the chart.

Of the 40 dragons produced, approximately 10 of them should be hornless and the rest horned. Introduce Punnett squares at this point to show the students how the genotype ratio can be derived . It is important for the students to realize that the idealized 3:1 ratio predicted by the Punnett square analysis is not always (or even usually) reflected in practice. Rather, the statistical prediction is that, in the overwhelming majority of cases, the ratio will come close to 3:1. If time permits, you may want to pool the data obtained by each group in the class to examine that the observed ratio comes closer to the predicted value when the size of the sample is increased.

This activity is to be followed by "Making Predictions."

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