1. A Fruit Fly Cross

2. Background information A recessive mutant allele, black, causes a very dark body in fruit flies, Drosophila, when homozygous. The wild-type color is described as gray.

3. So the Question is… What F 1 phenotypic ratio is predicted when a black female is crossed to a gray male whose father was black? Hint: Use B for the dominant trait

4. Time to Think…5 Steps Review the data Set up the problem Make your punnett square Look at your results Do they make sense?

5. And the Answer is… Since the female parent is black, she must be ________ for the mutant, recessive color (bb).

6. That was the answer because… The male parent is gray and thus he must have at least one dominant allele (B). Since his father was black (bb), and since he received one of the chromosomes from his father, the male parent must be heterozygous (Bb).

7. Look at the facts… So the female is bb (black) And the male is Bb (gray) Put them into a punnett square bb x Bb

8. And the results are… _______ % Gray _______ % Black 50