I have performed an experiment to study the response of a yeast (that contains 5000 genes) to stress caused by heat shock. I have one list of 48 genes that are overexpressed at 37ºC and another list of 145 genes that are overexpressed at 42ºC. There are 38 genes that are overexpressed in both of them.
By chance I expected only 1 gene overexpressed in both of them, how can I calculate if the overlap that I have obtained is significantly? How can I obtained the $p$ value? I know nothing about biostatistic or math software. Thanks you very much!!! Any help will be very welcome :)