This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Retinoblastoma gene is located on a chromosome - 
Select and explain. 
A. 13, B. 6, C. 9, D. 21
A: 13
Answer: A: 13 
Explanation: Location of retinoblastoma (RB) gene is 13 q 14
Deletion of a small number of tightly clustered genes result in a number of genetic disorders termed as microdeletion syndromes