Help with queries.

Dear group,

I just started learning postgres and I have to analyze my data. So
please bear with me, for all the simple questions that I am asking.
Apologies.

I have a table:

snps table

id | sample_id | chromosome | from | to |
----------------------------------------------------------------
1 1 chr1 10 11
2 1 chr1 14 15
3 2 chr1 14 15
4 2 chr1 9 10
5 3 chr1 14 15
6 3 chr14 35 36
7 3 chr14 39 40
8 2 chr14 39 40
9 2 chr14 43 44
10 1 chr14 43 44

gene table:

id | chromosome | from | to | genename
1 chr1 4 20 SRC
2 chr1 25 45 SRC
3 chr1 80 100 CSK
4 chr1 120 140 CSK

My aim is to for a gene in gene table (SRC that has two ranges 4-20 and 25-45),
I want to map all coordinates in snps table.
Then I want to get those entries where sample 1 and sample 2 have in
common and sample 1 and sampl3 in common.

I do not know how to get these entries. Could any one help me please.

thank you.

adrian