Final answer:
The deviation in the posies population's genotype frequencies from Hardy-Weinberg expectations could likely be explained by genetic drift, especially in a small population.
Step-by-step explanation:
A student has collected certain genotype data for a population of posies and has noticed a deviation from the expected Hardy-Weinberg predictions. Several plausible explanations for this deviation include balancing selection, negative frequency-dependent selection, inbreeding, and genetic drift. Considering the data provided, where certain genotypes appear more frequently than expected, genetic drift is a likely explanation, especially if the population size is relatively small. This phenomenon causes random fluctuations in allele frequencies and can result in the observed deviation from expected frequencies based on Hardy-Weinberg equilibrium.