Question

You cross a true breeding black guinea pig to a true breeding white guinea pig. In the F1 generation, you get all black guinea pigs. You cross the F1 generation together. What are the possible genotypes of the F2 generation?

Answer 1

When F1 black guinea pigs (genotype Bb) are crossed, the F2 generation can have genotypes BB, Bb, or bb with a genotypic ratio of 1:2:1 and a phenotypic ratio of 3 black to 1 white.

Step-by-step explanation:

When you cross a true breeding black guinea pig with a true breeding white guinea pig and get all black guinea pigs in the F1 generation, it implies that black is the dominant color trait. Therefore, all the F1 generation guinea pigs will have the genotype Bb (black color being represented by B and white color by b). When you cross the F1 generation (Bb x Bb), you are performing a monohybrid cross, and you can use a Punnett square to predict the possible genotypes of the F2 generation.

The possible genotypes from such a cross would involve three different combinations according to Mendelian genetics:

1. BB (homozygous dominant)
2. Bb (heterozygous)
3. bb (homozygous recessive)

Using a 4x4 Punnett square, the ratio of the genotypes in the F2 generation would be 1 BB : 2 Bb : 1 bb. This means that there is a 25% chance for a homozygous dominant (all black), 50% chance for a heterozygous (all black), and a 25% chance for a homozygous recessive (white), which sums up to a genotypic ratio of 1:2:1 for BB:Bb:bb, respectively. The phenotypic ratio, which reflects the observable characteristics, would be 3 black : 1 white.