Which of the following best describes gene expression? A. Each cell contains the code to make only one protein. B. All cells make all types of proteins at all times. C. Specific proteins are made only at certain times in certain cells. D. A person's phenotype can differ from his or her genotype.

## Step 1<br />Gene expression is the process by which the instructions in our DNA are converted into a functional product, such as a protein. This process is highly regulated and specific, meaning that not all genes are expressed at all times.<br /><br />## Step 2<br />Option A is incorrect because each cell contains the potential to make many different proteins, not just one. This is due to the fact that the DNA in each cell contains the instructions for making all the proteins needed by the organism.<br /><br />## Step 3<br />Option B is also incorrect. Not all cells make all types of proteins at all times. This is because different cells have different functions and therefore need different proteins.<br /><br />## Step 4<br />Option D is not directly related to gene expression. While it is true that a person's phenotype can differ from his or her genotype, this is due to environmental factors and not the process of gene expression itself.<br /><br />## Step 5<br />Option C is the correct answer. It accurately describes the process of gene expression. Specific proteins are made only at certain times in certain cells, which is a reflection of the highly regulated and specific nature of gene expression.