Final answer:
The expected phenotypic ratio from the cross between two guinea pigs that are heterozygous for both traits is 3:1, meaning that for every 3 guinea pigs with the dominant trait, there will be 1 guinea pig with the recessive trait.
Step-by-step explanation:
The expected phenotypic ratio from the cross between two guinea pigs that are heterozygous for both traits can be determined using a Punnett square. Let's use the example of two guinea pigs that are heterozygous for coat color, with the dominant allele (A) representing black coat color and the recessive allele (a) representing white coat color. The possible genotypes for the parents are Aa x Aa.
The Punnett square for this cross would look like:
AaAAAAaaAaaa
From the Punnett square, we can see that the expected phenotypic ratio for the offspring is 3:1. This means that for every 3 guinea pigs with the dominant black coat color (AA or Aa), there will be 1 guinea pig with the recessive white coat color (aa).