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: Biochemistry
In the mammalian genome, maximum number of genes code for the receptors of: 
Select and explain. 
A. Immunoglobulin receptors, B. Interleukins, C. Growth factors, D. Odorants
D: Odorants
Answer: D: Odorants 
Explanation: Ans: D. OdorantsIn the mammalian genome, maximum number of genes code for the receptors of odorants."The olfactory receptor (OR) genes constitute the largest gene family in mammalian genomes.Humans have >1,000 OR genes, of which only -40% have an intact coding region and are therefore putatively functional.Odorant receptor genes form the largest gene family in the genome of many animals: for example, the mouse genome contains approximately 1200 of these genes.