Teacher Version


Name: ______________________                Date: ______________

A Horns Activity: Writing Rules:  Generalizing from data

Dragons have two different ways to express the horn genes. They can have horns or be "hornless."   The rule for horns is:

HH, Hh, and hH gives horns, hh gives no horns.

1.      Try to answer the following questions without looking at the computer.  You may use the horns rule (above) as an example:

Not all dragons have the same number of legs. How many ways can the legs genes be expressed? ________

What is the rule for legs?

Dragons have three ways to express the legs genes: 4, 2 and 0. The rule is LL for 4, Ll for 2 and ll for 0 legs.

2.       How many ways can the wings genes be expressed? ________
What is the rule for wings?
There are two ways to express the wings genes: No wings and wings. WW, Ww and wW is no wings, ww has wings. 3.      Now that you have written rules for these other dragon traits, use GenScope to check your work. If you want to add or change anything that you wrote above now that you've looked at GenScope, do not change the answers above - just rewrite the information below. New information about legs:  
New information about wings:
    The first part of this exercise is straight recall.

We ask the student to recall what the alleles for the different traits are and then to write a rule for that trait. This builds on the previous exercise. The next direction takes the kids to the computer to check their work and to make corrections when necessary. The last two questions require multilevel thinking.

4.       Do you notice anything special about these traits and their rules? That is, are they similar or different from the rule for horns? Explain below.

5.       Why is it important to look at the similarities and differences? What does it mean to have different patterns of inheritance? Explain below.

The students will compare the rules they have devised to the rule for horns which we gave them and will decide whether the rules are the same or different from the one for horns. They will write why they think there is a difference or a similarity and then try to explain what they think it all means.

The rule for horns is that H plus anything else gives horns, hh gives no horns. The rule for legs is LL gives 4 legs and ll none. (Incomplete dominance.) For wings, W plus anything else gives no wings, ww gives wings. All the traits except legs are examples of simple dominant/recessive rules.

Again, we are asking the student to do something which is very hard. We are asking them to put into words the differences or similarities between the different rules. Once they have written their reasons down, they aren't through. They have to explain why. In order to explain why, they must mentally review everything they have learned about the relationship between two alleles for a trait and the effect of that relationship on the phenotype of the organism. The fundamental rules of genetics must be recalled and applied to each set of alleles, since the mode of inheritance may differ from horns. And we wonder why they have trouble articulating the answers to these questions!

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