A Fruit Fly Cross

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 F1 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 50