Complete the following monohybrid cross.
Two parents that are heterozygous for brown eyes. Be sure to identify the genotypes of the parents, complete the Punnett square, identify the phenotypes with genotypes and the ratio of the phenotypes.
What percent of the offspring have blue eyes?
My answer: 25% of the offspring would have blue eyes if the parents are heterozygous.
What I need help with: How do I fully answer the question? Please help me.
Assuming that both of the heterozygous parents have both blue and brown genes, and blue is recessive to brown, e.g., Bb.
Construct a Punnett square and continue from there.
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To fully answer the question, you need to provide the genotypes and phenotypes for the offspring, as well as the ratio of the phenotypes.
Step 1: Identify the genotypes of the parents.
The question states that both parents are heterozygous for brown eyes, so their genotypes would be Bb (capital B represents the dominant allele for brown eyes, and lowercase b represents the recessive allele for blue eyes).
Step 2: Create a Punnett square.
A Punnett square is a diagram used to predict the possible genotypes of the offspring. Since both parents are heterozygous (Bb), the Punnett square would look like this:
B b
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B | BB | Bb |
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b | Bb | bb |
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Step 3: Identify the phenotypes with genotypes.
To determine the phenotypes, you need to determine which combinations of alleles lead to each eye color. The dominant allele (B) codes for brown eyes, while the recessive allele (b) codes for blue eyes. So, using the Punnett square:
- BB genotype represents individuals with brown eyes.
- Bb genotype represents individuals with brown eyes (as capital B is dominant).
- bb genotype represents individuals with blue eyes.
Step 4: Determine the ratio of phenotypes.
Count the number of individuals with each genotype from the Punnett square. In this case, there are two possible genotypes that result in individuals with brown eyes (BB and Bb) and one genotype that results in individuals with blue eyes (bb). Thus, the ratio of phenotypes would be:
- 2 individuals with brown eyes (BB and Bb)
- 1 individual with blue eyes (bb)
So, the ratio of the phenotypes is 2:1 (brown eyes:blue eyes).
Step 5: Calculate the percent of offspring with blue eyes.
To calculate the percentage, divide the number of individuals with blue eyes (1) by the total number of offspring (3) and multiply by 100:
(1/3) x 100 = 33.33%
Therefore, 33.33% of the offspring would have blue eyes if both parents are heterozygous for brown eyes.