In Guinea pigs, black fur (B) is dominant over white fur ( b). Cross a heterozygous (hybrid) black guinea pig with a homozygous (purebred) white guinea pig. Complete a Punnett square, identify genotype, phenotypes, and probability and fraction that the offspring will be black and white.
To complete a Punnett square and determine the genotype, phenotype, and probability of offspring color, we need to understand the rules of genetics with respect to dominant and recessive alleles.
In this case, black fur (B) is dominant over white fur (b). The heterozygous black guinea pig can be represented as Bb (one copy of the dominant allele and one copy of the recessive allele), while the homozygous white guinea pig is represented as bb (two copies of the recessive allele).
To create a Punnett square, we list the possible alleles that each parent can contribute along the top and left side. In this case, the heterozygous black guinea pig can contribute either a B or a b allele, while the homozygous white guinea pig can contribute only a b allele.
Punnett square:
| B | b |
----|-----|-----|
B | BB | Bb |
b | Bb | bb |
Now we can determine the genotype and phenotype of the offspring:
- Genotype: From the Punnett square, we see that the possible genotypes of the offspring are BB, Bb, Bb, and bb.
- Phenotype: The BB and Bb genotypes will result in black fur, represented by the dominant allele (B), while the bb genotype will result in white fur, represented by the recessive allele (b).
So, the possible phenotypes are black and white fur.
To calculate the probability and fraction of the offspring being black or white, we count the number of each genotype and divide by the total number of possibilities.
- Probability of black fur: There are three possible genotypes that result in black fur (BB, Bb, Bb) out of a total of four possible genotypes. Therefore, the probability of black fur is 3/4 or 0.75 (75%).
- Probability of white fur: There is one possible genotype that results in white fur (bb) out of a total of four possible genotypes. Therefore, the probability of white fur is 1/4 or 0.25 (25%).