This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Introduction, Subject name: Pathology
The approx. number of genes contained in the human genome is: 
Select and explain. 
A. 40,000, B. 20,000, C. 80,000, D. 1,00,000
B: 20,000
Answer: B: 20,000 
Explanation: There are roughly 3.2 billion DNA base pairs in the human genome. Out of the total genome there are about 20,000 protein encoding genes,which comprises only 1.5% of the genome.