A cross between a blue fish with the genotype Bb (dominant allele) and a white fish with the genotype bb (recessive allele) produces offspring with white scales. Which option correctly illustrates this genetic cross

Answer 1

To illustrate the genetic cross between a blue fish with the genotype Bb and a white fish with the genotype bb, we can use a Punnett square. Here’s how you set up the square:

1. Parent Genotypes:

   • Blue fish: Bb (heterozygous for blue scales)
   • White fish: bb (homozygous for white scales)

2. Gametes:

   • The blue fish (Bb) can produce two types of gametes: B (dominant allele) and b (recessive allele).
   • The white fish (bb) can only produce one type of gamete: b (recessive allele).

3. Punnett Square:

   | | b | b | |-----|-----|-----| | B | Bb | Bb | | b | bb | bb |

4. Offspring Genotypes:

   • Bb: 2 offspring (blue scales, since B is dominant)
   • bb: 2 offspring (white scales, since b is recessive)

5. Offspring Phenotypes:

   • 2 Blue fish (Bb)
   • 2 White fish (bb)

6. Ratios:

   • 2 blue fish : 2 white fish, which simplifies to a 1:1 ratio.

However, since the cross results in 50% Bb (blue) and 50% bb (white), the expected phenotype ratio would be as follows:

• 50% Blue fish (Bb)
• 50% White fish (bb)

Since your description states that the offspring produced have white scales, it's important to clarify that while Bb individuals (which are blue) are also produced, the statement indicates a focus on the recessive white phenotype (bb).

In conclusion, the Punnett square effectively demonstrates the genetic cross between the blue fish and white fish and shows the potential outcomes for the offspring.