For hair color, Brown (B) is a dominant trait and Blond (b) is a recessive trait. If one parent has pure blond hair and one parent has hybrid brown hair, complete the Punnett square and questions that follow.
a) What is the probability that their first child will have pure brown hair?
b) What is the probability that their first child will have blond hair?
c) What is the probability that their first child will have brown hair?
To complete the Punnett square, we need to know the genotypes of the parents. Let's assume that the parent with pure blond hair has the genotype bb (which means both alleles are recessive), and the parent with hybrid brown hair has the genotype Bb (one dominant allele and one recessive allele).
Now, let's fill in the Punnett square:
| b | b |
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B | Bb | Bb |
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b | bb | bb |
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a) The probability that their first child will have pure brown hair (BB) is 0%, since neither parent has the dominant allele for brown hair.
b) The probability that their first child will have blond hair (bb) is 50%. This is because the parent with pure blond hair (bb) can only pass down the recessive allele for blond hair.
c) The probability that their first child will have brown hair (Bb) is also 50%. This is because the parent with hybrid brown hair (Bb) can pass down either the dominant allele for brown hair or the recessive allele for blond hair.
To determine the probabilities, we need to create a Punnett square based on the parental hair color traits. Let's represent pure brown hair with the symbol B and blond hair with the symbol b.
The parent with pure blond hair has the genotype bb, while the parent with hybrid brown hair has the genotype Bb.
To create the Punnett square, we cross the alleles from one parent's genotype with the alleles from the other parent's genotype.
Here is the Punnett square for the given scenario:
| b | b |
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B | Bb | Bb |
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b | bb | bb |
a) Based on the Punnett square, there are two possible genotypes for the child to have pure brown hair: Bb. Thus, the probability of their first child having pure brown hair is 2/4 or, simplifying, 1/2.
b) Similarly, based on the Punnett square, there are two possible genotypes for the child to have blond hair: bb. Hence, the probability of their first child having blond hair is 2/4 or 1/2.
c) To calculate the probability of their first child having brown hair, we need to consider both the pure brown genotype (Bb) and hybrid brown genotype (Bb). In the Punnett square, there are four possible genotypes that result in brown hair: Bb, Bb, Bb, and Bb. Therefore, the probability of their first child having brown hair is 4/4 or 1.