In rabbits, the allele for black fur color (B) is dominant to the allele for brown fur color (b), and the allele for short fur (F) is dominant to the allele for long fur (f).

Question

If a cross between two rabbits that are heterozygous for both traits results in 16 offspring, how many of the offspring can be expected to have short brown fur?
A 1
B 3
C 9
D 7

Answer 1

To solve this problem, we need to use a Punnett square to find the expected genotypic ratio of the offspring from a cross between two rabbits that are heterozygous for both traits (BbFf x BbFf).

1. Determine the possible gametes from the parents:

   • Each parent can produce the following gametes: BF, Bf, bF, bf.

2. Set up the Punnett square:

               BF         Bf         bF         bf
            ______________________________________
         BF |   BBFF   |   BBFf   |   BbFF   |   BbFf   |
            |______________________________________
         Bf |   BBFf   |   BBff   |   BbFf   |   Bfff   |
            |______________________________________
         bF |   BbFF   |   BbFf   |   bbFF   |   bbFf   |
            |______________________________________
         bf |   BbFf   |   Bfff   |   bbFf   |   bfff   |
   

3. Count the offspring types:

   • We are interested in the number of offspring that have short brown fur (bbF-). The criteria are:

     • The offspring must be homozygous for the brown fur allele (bb).
     • The offspring must have at least one dominant allele for short fur (F-).

   • Looking at the Punnett square, we can find these combinations:

     • From bbFF: 1 (bbFF)
     • From bbFf: 2 (bbFf)

   So, the total number of offspring with short brown fur (bbF-) is:

   • 1 (bbFF) + 2 (bbFf) = 3.

4. Conclusion: The expected number of offspring with short brown fur is 3.

The answer is B 3.