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In a certain species, the allele for blue flowers (B) is dominant over the allel

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Question: In a certain species, the allele for blue flowers (B) is dominant over the allele for white flowers (b). If two blue-flowered plants, both heterozygous (Bb), are crossed, what is the expected phenotypic ratio of the offspring?

Options:

  1. 1:1
  2. 3:1
  3. 1:2:1
  4. 2:1

Correct Answer: 3:1

Solution: 

The cross Bb x Bb results in a phenotypic ratio of 3 blue (BB or Bb) to 1 white (bb), which is 3:1.

In a certain species, the allele for blue flowers (B) is dominant over the allel

Practice Questions

Q1
In a certain species, the allele for blue flowers (B) is dominant over the allele for white flowers (b). If two blue-flowered plants, both heterozygous (Bb), are crossed, what is the expected phenotypic ratio of the offspring?
  1. 1:1
  2. 3:1
  3. 1:2:1
  4. 2:1

Questions & Step-by-Step Solutions

In a certain species, the allele for blue flowers (B) is dominant over the allele for white flowers (b). If two blue-flowered plants, both heterozygous (Bb), are crossed, what is the expected phenotypic ratio of the offspring?
  • Step 1: Identify the alleles. The allele for blue flowers is 'B' (dominant) and the allele for white flowers is 'b' (recessive).
  • Step 2: Determine the genotypes of the parent plants. Both parent plants are heterozygous, meaning they have one of each allele: 'Bb'.
  • Step 3: Set up the Punnett square. Create a 2x2 grid to show the possible combinations of alleles from the two 'Bb' parents.
  • Step 4: Fill in the Punnett square. The combinations will be: BB (from B and B), Bb (from B and b), Bb (from b and B), and bb (from b and b).
  • Step 5: Count the genotypes. The results from the Punnett square are: 1 BB, 2 Bb, and 1 bb.
  • Step 6: Determine the phenotypes. BB and Bb both result in blue flowers, while bb results in white flowers.
  • Step 7: Calculate the phenotypic ratio. There are 3 blue flowered plants (1 BB + 2 Bb) and 1 white flowered plant (1 bb), giving a ratio of 3 blue to 1 white.
  • Step 8: Write the final ratio. The expected phenotypic ratio of the offspring is 3:1.
  • Mendelian Genetics – Understanding dominant and recessive alleles and how they affect phenotypic ratios in offspring.
  • Punnett Square – Using a Punnett square to predict the genotypic and phenotypic outcomes of genetic crosses.
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