Question

In the cross Bb x Bb (two heterozygous mice), what percentage of the offspring would you predict to have the same phenotype as the parents?

0%

25%

50%

75%

100%
Next, you perform a cross with a mouse with black fur and a mouse with white fur. Which result(s) for the offspring would confirm that the mouse with black fur was heterozygous?

4 mice with black fur

8 mice with black fur, 1 mouse with white fur

5 mice with black fur, 6 mice with white fur

6 mice with black fur, 2 mice with white fur

Answer 1

- For Bb x Bb: 75% of the offspring will have the same (dominant black) phenotype as the parents.

- For the black x white (white = bb) cross: any offspring that are white (bb) prove the black parent carried a b allele (i.e. was Bb). So the results that would confirm the black parent was heterozygous are:
- 8 black, 1 white
- 5 black, 6 white
- 6 black, 2 white

(4 black, 0 white would not confirm heterozygosity.)