In guinea pigs, black cot is dominant to albino. Rough coat us dominant to smooth coat. A black smooth guinea pig was mated with an albino rough guinea pig. Their offspring were black rough and black smooth. If these were the only produced over a period of years of matings, what was the possible genotype of each parent?

Question

In guinea pigs, black cot is dominant to albino. Rough coat us dominant to smooth coat. A black smooth guinea pig was mated with an albino rough guinea pig. Their offspring were black rough and black smooth. If these were the only produced over a period of years of matings, what was the possible genotype of each parent?

Answer 1

To determine the possible genotypes of the parent guinea pigs, we need to analyze the phenotypes of their offspring. Let's start by assigning letters to represent the different traits:

- Black coat color is dominant to albino, so we will use "B" to represent black and "b" to represent albino.
- Rough coat is dominant to smooth coat, so we will use "R" to represent rough and "r" to represent smooth.

Now, let's examine the traits of the offspring from the given mating:

1. Some offspring were black rough. This means they must have inherited the dominant black color (B) and the dominant rough coat (R). Therefore, we know the genotype of these offspring is B_R_.

2. Some offspring were black smooth. This means they must have inherited the dominant black color (B), but they have a recessive smooth coat (rr). Therefore, we know the genotype of these offspring is B_rr.

Now, let's determine the possible genotypes of each parent by working backward based on the offspring's genotypes:

1. From the information provided, we know that one parent is black and smooth (B_rr). This parent must have the genotype B_rr since the offspring inherited the recessive smooth coat (rr) from this parent.

2. The other parent produced both black rough (B_R_) and black smooth (B_rr) offspring. To have a mix of rough and smooth offspring, this parent must be heterozygous for the rough/smooth coat trait, meaning its genotype could be either Rr or rR (because the order doesn't matter for codominant pairs). However, since it mated with the smooth-coated (rr) parent, we can conclude that this parent is Rr.

In summary, the possible genotype of the black smooth guinea pig is B_rr, and the possible genotype of the albino rough guinea pig is Rr.

Answer 2

To determine the possible genotypes of the parent guinea pigs, we need to analyze the phenotypes of their offspring. Let's start by assigning letters to represent the different traits:

One is either BBss or Bass; the other is aaRs or aaRR. Which combination would always give a Black coat and only sometimes a smooth coat?