The data provided on the body size of mice suggests a range of sizes, indicating that the trait is likely influenced by multiple genes rather than a single gene with complete dominance. The presence of various size categories (very small, small, average, large, very large) and the distribution of the number of mice across those categories suggests a continuous variation in traits rather than distinct categories.
Therefore, the inheritance pattern that this trait follows in mice is polygenic inheritance.
This type of inheritance involves multiple genes contributing to a single trait, resulting in a range of phenotypes, which aligns with the data you've presented.