Step 2: Hypothesize

Fruit flies can have wing shapes that are different from the normal (or "wildtype") straight wings of most flies. One of those traits is called "curly", which causes the wings to curl upward. Flies with this trait cannot actually fly, but instead hop around to move. Scientists are not 100% sure how this trait is inherited, although several experiments have suggested that it is dominant.

Wildtype Curly

In order to test the inheritance of the curly trait for ourselves, we will be crossing wildtype females with curly males. In order to best come up with your hypothesis, answer the questions below. Please note that although here a letter has been used to represent the wildtype genotype, in the research community wildtype flies are represented by "+" symbols.

What Results Should You Expect?

1. Recessive traits are represented by which type of letters?
Capital.
Lowercase.
Vowels.
Consonants.

2. According to the work of other scientists, the curly trait is dominant. Therefore, what should we predict the genotype of a heterozygous curly fly to be?
Yy.
YY.
yy.

3. If the wildtype fly we use in our cross is homozygous, what is its genotype?
Yy.
YY.
yy.

4. On a separate sheet of paper, show the cross of the wildtype female to the curly male using a Punnett square (shown below). What percentage of the offspring in the F1 (first generation) will be curly?
50%.
75%.
100%.
0%.

5. According to your Punnett square, what percentage will be wildtype?
50%.
75%.
100%.
0%.

6. All the offspring that are curly will have what genotype?
yy.
YY.
Yy.

7. On your Punnett square, you wrote letters above each space. What does each single letter represent?
A complete genotype.
A body cell that contains a gene from the parent.
A gamete that contains a gene from the parent.
A gamete that contains one allele of the gene from the parent.

8. A heterozygous fly (Yy) would have the same phenotype as a homozygous dominant fly (YY). Why is this so?
Since the Y allele causes the fly to have at least half its proteins for curly wing development, this is enough for the fly to have curly wings.
This is false; since a heterozygous fly has only half the proteins for curly wing development it will still have normal wings (and therefore have a different phenotype from the YY fly).
The big Y is capital and therefore stronger than the little y, so the heterozygous fly will have curly wings just like the homozygous dominant fly.