This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Which of the following techniques is used for detection of variation in DNA sequence and Gene expression? 
Select and explain. 
A. Nohern blot, B. Southern blot, C. Western blot, D. Microarray
D: Microarray
Answer: D: Microarray 
Explanation: DNA microarray (also commonly known as DNA chip or biochip) is a collection of microscopic DNA spots attached to a solid surface. Scientists use DNA microarrays to measure the expression levels of large numbers of genes simultaneously or to genotype multiple regions of a genome.