In rats, offspring of larger mothers tend to be larger than offspring of smaller mothers, even when fed the same diet and raised apart from their mothers. When fed higher calorie diets, rats tend to be larger than rats fed lower calorie diets, even when they are offspring of the same mother. These two experimental results suggest that rat body size is influenced by which factors

The correct answer would be - environmental and genetic (allelic) factors.

Explanation:

The phenotype of an animal can be manipulated or affected by the change in gene expression through environmental factors. Environmental factors can be temperature, diet, oxygen level, light, and many other abiotic factors. In this case, diet is affecting the phenotype of the rats that eat high-calorie diets.

Genetic or allelic factors are also expressed in this case as the size of the rats also depends on the size of the mother rat which means that there are some genes also carry these traits