In guinea pigs, black hair (B) is dominant to brown hair (b) and short hair (H) is dominant to long hair (h). A black, short-haired guinea pig (BBHH) is crossed with a brown short-... In guinea pigs, black hair (B) is dominant to brown hair (b) and short hair (H) is dominant to long hair (h). A black, short-haired guinea pig (BBHH) is crossed with a brown short-haired guinea pig (bbHh). What is the phenotype ratio that will be seen in the offspring?
Understand the Problem
The question is asking for the phenotype ratio of the offspring produced from a genetic cross between a black, short-haired guinea pig (BBHH) and a brown short-haired guinea pig (bbHh). To solve this, we will first determine the possible gametes from each parent and then use a Punnett square to identify the phenotype ratio of the offspring.
Answer
The phenotype ratio of the offspring is $2:0$.
Answer for screen readers
The phenotype ratio of the offspring is $2:0$.
Steps to Solve
- Identify the genotypes of the parents
The genotypes of the guinea pigs are:
- Black, short-haired: $BBHH$
- Brown, short-haired: $bbHh$
- Determine the possible gametes from each parent
For the first parent ($BBHH$), the only possible gamete is:
- $BH$
For the second parent ($bbHh$), the possible gametes are:
- $bH$
- $bh$
- Construct a Punnett square
The Punnett square will have the possible gametes of each parent as follows:
| $bH$ | $bh$ | |
|---|---|---|
| $BH$ | $BbHH$ | $BbHh$ |
- Identify the genotypes of the offspring
From the Punnett square, we see the genotypes of the offspring:
- $BbHH$
- $BbHh$
- Determine the phenotypes of the offspring
Now we can analyze the genotypes to identify phenotypes:
- $BbHH$: Black, short-haired (since black is dominant over brown)
- $BbHh$: Black, short-haired (as heterozygous for color but homozygous for hair)
- Calculate the phenotype ratio
Both offspring are black, short-haired. Therefore, the phenotype ratio is:
- Black, short-haired: 2
- Brown, short-haired: 0
The ratio simplifies to: $$ 2:0 $$
The phenotype ratio of the offspring is $2:0$.
More Information
All offspring from this cross are black and short-haired due to the dominance of the black color allele (B) over the brown color allele (b) and the dominance of the short-haired allele (H) over any recessive alleles.
Tips
- Forgetting to identify dominant and recessive traits, which can lead to inaccurate phenotype predictions.
- Miswriting genotypes or gametes in the Punnett square.
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