A researcher wanted to create a loss of function mutation for studying Type I Diabetes in a model animal. What mutation would mimic Type I diabetes

A knockout mutation in which the gene is "erased" through a nonsense mutation. In this way, the gene that codes for insuline would be eliminated, and no insuline would be produced.

Explanation:

Type I diabetes is a chronic disease in which no insulin or too little insuline is produced by the pancreas. There are many factors that can trigger Type I diabetes, including genetics and certain viruses. Although Type I diabetes is more likely to appear during childhood or adolescence, it can also begin in adulthood. It is a disease that cannot be cured but can be treated, and treatment focuses on controlling blood sugar levels with insulin injections and a controlled diet.

Insulin is produced by beta cells in the islets of Langerhans of the pancreas. It is a hormone used to allow glucose to enter the cells to produce energy, helping to transport the sugar from the blood to the other tissues of the body. So, through glycolysis and cellular respiration, the necessary energy is obtained in the form of ATP.  

So, we could consider that the gene coding for insulin is not working properly or not working at all. So, a mutation that would mimic Type I diabetes is a knockout mutation in which the gene is "erased" through a nonsense mutation (a point mutation in DNA that results in the appearance of a premature termination codon, so the synthesis of the protein ends earlier, it is not completed). In this way, the gene that codes for insuline would be eliminated, and no insuline would be produced. This type of mutation can be achieved in a laboratory and rhis results in organisms that do not express the gene in a specific tissue or in the whole organism.