GS Activity: Mutations (Teacher Version)

Name _______________________________ Date _______________

Mutations Activity: Understanding the connection between changes in DNA and phenotype

GenScope File: Dragon

A mutation is an alteration in the DNA of an organism. When the DNA is changed, the action of the gene is changed and the resulting trait is different from the original.

Open GenScope using the Dragon file and click on the second button to produce a male dragon. Before you start messing around with the DNA, use the chromosome tool to bring up chromosome 1 which contains the horn gene. Click on the alleles on both chromosomes and refresh your memory about what happens to the organism with each combination of alleles.

1. What are the rules for horns?

HH gives _______

Hh gives _______

hH gives _______

hh gives _______

The student should answer that HH, Hh and hH all give horns, hh gives no horns.

This exercise is designed to refresh the memory about a previous exercise. It requires the student to go back and forth between the chromosomes window and the organism window to observe what the effect on the phenotype is when the genotype is changed. This will reinforce the idea of cause and effect, we hope.

2. Now, do the same for wings. Write the rules for the inheritance of this trait, and test your answers. Hint: To test patterns of inheritance, the alleles should be combines in various combinations - like and unlike.

What are the rules for wings?

W W gives __________
W w gives __________
w W gives __________
w w gives __________

These are the "Rules" for inheritance of this trait in dragons. That was easy, wasn't it? The student should fill out the chart by writing that W W, W w and w W gives no wings and w w gives wings.

3. Now lets make a mutation. Using the chromosome tool, open up the chromosome window if it isn't already open. Click on the DNA button. The cursor will turn into a rectangular magnifying glass when it is passed over the chromosome. Center it over the Color A gene on the X chromosome and click. A new window, the DNA window, will appear. If you add some of the four bases (Adenine, Thymine, Cytosine, Guanine) or delete some, then click on the Apply button, you will create a mutation. Go back to the chromosome window and check the menu for the Color A allele on the chromosomes. There should be a new allele listed, aw. Change both alleles to aw and watch what happens to your dragon in the organism window. Now determine what the rule of inheritance is for the albino gene and write it in the space below. Do the same for wings.

To do this, test the mutated gene in the same way that you tested the non-mutated genes: Change the menu for the gene on the chromosome so that you have 2 alleles the same, 2 unlike alleles, allele + mutated alleles and 2 mutated alleles. As you make the changes on the chromosomes, watch what happens to the dragon in the organism window.

What are the rules for Color A? A    A          ____________
A    a          ____________
a     A         ____________
a     a         ____________
A     aw     ____________
aw   A       ____________
a      aw     ____________
aw   a        ____________
aw   aw     ____________
A      -         ____________
a      -          ____________
aw   -          ____________ The chart does not show the B gene for color. To get the full range of color (4) in males, you have to change the B alleles also since color is polygenic. AA, Aa, aA with Bb or bB gives Bronze. AA or Aa or aA with BB gives Topaz. aa with Bb or bB gives Azure and aaBB gives amethyst. aw with A_ gives whatever color A would give, depending on the B gene. aw with a_ gives whatever color a would give depending on the B gene again. aw aw gives albino. In females, A-/B- gives emerald, a-/B- gives gold and aw-/B- gives albino.

The full impact of the intricacy of color inheritance is finally felt here. Because color is polygenic (two genes, interacting, determine color in dragons) the inheritance pattern in necessarily complex. By watching the organism window as the allele combinations are changed, the student can see what the effect is. Of course, we must not forget to mention that the DNA window, a third level, is seen by the student as s/he manipulates the gene. In this way, s/he can actually see the effect of changing the DNA immediately - "up close and personal" - something that you can't do without a computer!

Wings:

W W gives     ____________
W w gives      ____________
w W gives      ____________
w w gives       ____________
W ww gives   ____________
w ww gives    ____________
ww ww gives ____________

When the student fills out the chart, s/he should write W W, W w, and wW gives no wings. W w gives wings, W ww, gives wings, w ww gives double wings and ww ww causes the dragon to die (lethal).

Aside from the fact that having wings is recessive, which is always jolting to the students, a new dimension is added in this problem. Having a double set of the ww allele causes the dragon to die. In real life, there are many mutations which are lethal. This is another case of trying to bridge the gap between the model and the real world.

4. Now, using this information, can you come up with a general rule which would apply to the inheritance of other mutations? Write it in the space below.

Mutations are usually, but not always recessive. Some mutations can be lethal if the allele is present as a double dose.

The most difficult task for almost everyone, adult or student, is to take data and make a generalization from them. By leading the kids through this exercise, we hope that they will get some much needed practice. In this way, they should be able to make the jump from modeling to real life.

5.       There are more mutations. See if you can find them. Write the various combinations of alleles and what the phenotype is for each in the table below: a. firebreathing:
F    F   _____________
F    f    _____________
F    -    _____________
f     f    _____________
f     -    _____________
F    ff   _____________
f     ff   _____________
ff    ff   _____________
ff    -    _____________

F F, F f, F             are non-firebreathing
f f, f-                       breathe fire
F ff, f ff, ff ff, ff -      breathe blue fire

b. Horns:
H h       _____________
H H      _____________
h h       _____________
H hh    _____________
h hh     _____________
hh hh _____________

H h, HH                      have horns
h h                              no horns
H hh, h hh, hh hh        unicorn horn

6. Call your teacher over to see your tables. Do these mutations follow the general rule you wrote?

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