Final answer:
The genetic cross between heterozygous and homozygous recessive flies that yielded a P value of 0.25 indicates no significant deviation from Mendel's law of independent assortment. The traits in question appear to assort independently, and any discrepancies from the expected ratio are likely due to chance.
Step-by-step explanation:
When a student performs a dihybrid test cross between flies that are heterozygous (one dominant and one recessive allele) for both traits and flies that are homozygous recessive for both traits, the assumption underlying the predicted outcome is that the traits will assort independently according to Mendel's law of independent assortment. If the P value from the experiment is determined to be 0.25 and considered insignificant, suggesting a good fit, the conclusion is that there is no statistical evidence to reject the hypothesis that the two genes are assorting independently. This means that the observed deviation from the expected 1:1:1:1 phenotypic ratio is likely due to random chance rather than a violation of independent assortment or linkage between the genes.
The analysis would suggest that the two traits are being inherited in a manner consistent with Mendel's second law, which states that alleles for different genes assort into gametes independently of one another—as long as they are not linked on the same chromosome. Therefore, even if there is variation from the predicted ratio, as long as the variation is not statistically significant, the results still support the law of independent assortment.