Final answer:
The phenotypic ratio for the offspring of two sea stars that are heterozygous for both color and tube feet length is 9:3:3:1, representing a dihybrid cross with independent assortment of the traits.
Step-by-step explanation:
The phenotypic ratio of a cross between two sea stars that are heterozygous for both orange or yellow color and long or short tube feet traits can be determined by setting up a Punnett square for a dihybrid cross. Let's use O for the dominant orange allele, o for the recessive yellow allele, L for the dominant long tube feet allele, and l for the recessive short tube feet allele. Since they are heterozygous for both traits, each sea star's genotype is OoLl.
According to the rules of inheritance, specifically the principle of independent assortment, we would expect to see a 9:3:3:1 phenotypic ratio in the offspring, when traits are not linked. This means out of a sum of 16 possible combinations from a dihybrid cross, there would typically be 9 offspring with the dominant phenotype for both traits (orange, long tube feet), 3 offspring with the dominant phenotype for the first trait and recessive for the second (orange, short tube feet), 3 offspring with the recessive phenotype for the first trait and dominant for the second (yellow, long tube feet), and 1 offspring with the recessive phenotype for both traits (yellow, short tube feet).