Final answer:
Two genetically identical Agouti mice exhibited different appearances due to environmental factors affecting gene expression, resulting in one being yellow and fat while the other brown and thin, highlighting epigenetic influence on phenotype.
Step-by-step explanation:
The two genetically identical Agouti mice had different appearances due to b) Environmental factors affecting gene expression. Even though the mice were clones, with identical genetic material, the expression of their genes changed in response to environmental conditions. This phenomenon illustrates how nongenetic factors can influence phenotype, resulting in significant differences such as one mouse being yellow and fat, while the other is brown and thin. This is an example of how identical genetic makeup can yield different phenotypes due to epigenetic modifications and the impact of external factors on how genes are expressed, suggesting that the answer is not related to genetic differences, mutations, or randomness.
Understanding the interaction between genetic predispositions and environmental influences sheds light on topics such as epistasis and gene expression patterns that contribute to diverse characteristics within a species.