A Horn Activity: Making Predictions: Learning how to make intelligent guesses
GenScope File: HornsExperiment.gs
In the Horns Experiment, you made forty babies! That's a BIG family! You started with a Mom and Dad who both had horns. You noticed that most of their babies had horns, just like their parents, but some of them (approximately one quarter) were hornless.
Today, you will make some predictions about the babies from these very same parents OFF THE COMPUTER. Then you will use GenScope to check your predictions about the outcomes. Don't worry if your predictions do not come true -that's part of the fun of science!
Just to remind you, here's what the
parent dragons look like:
1. Note that neither one of the parents has wings. What do you think the babies will look like? Select one answer and make a check mark next to it.
___ A few (fewer than half) of the babies will have wings.
___ Most of the babies will have wings.
___ All of the babies will have wings.
Since having wings is a recessive trait,
many of the students will run into trouble. They are used to the concept
that having a trait means that the trait is dominant. This reversal of
the usual is difficult for some of the students to deal with at first.
Since they think of having wings as dominant, a lot of them will say that
none of the babies will have wings.
Most of the students have little trouble remembering that it takes LL to produce 4 legs, Ll two legs and ll no legs. They rarely make mistakes in this part of the problem. A helpful hint, in case they do have trouble, is to remind them that anytime they have 3 different phenotypes, it usually indicates 2 alleles which are incompletely dominant. to each other. Many students may say that the offspring will have two legs without actually going through the detailed reasoning that justifies such a prediction, just on the basis that two is the average of four and zero. It is important that they eventually come to realize that it is the allelic combinations that create the offspring's phenotype. One way to get them to reflect on this is to ask them what will happen when two two-legged parents mate. In contrast to the zero- and four-legged phenotypes, two-legged dragons do not "mate true" because their alleles can mix in three different ways, corresponding to all three possible phenotypes.
These questions require good recall
of various traits dealt with in former puzzles on the computer. They also
serve as a gentle quiz to determine how many of the basic genetics rules
the students remember, and how well they can apply them. As for what they
learn from this exercise, the answers will vary from wonderfully complex
ones about learning genetics per se to more prosaic ones about checking
your work to avoid surprises.