![the common area under the two distribution curves for Normal and case ][1]

https://www.dropbox.com/s/z36psl4ct8031qo/Screen%20Shot%202017-07-05%20at%2012.25.14.png?dl=0

I want to find the normal distribution for the case and normal samples in microarray then intersect them to find the common area under the two distribution curves for Normal and case samples in Microarray as in the pictuer.

I am not sure how to find the normal distribution. Do I have to find the mean and SD for the normal samples as a one matrix ? or Do I have to find the normal distribution for each gene?

any help will highly appreciated