Help Replace value based on a logic statement

Hi All,
i need help to make an logic statement for my data.
i have this data:

1# T/T
2# C/C

4# T/T
5# T/C
6# T/C
7# T/C
8# C/C
9# T/T
10# T/T

Based on information, I want to replace whatever (T/T)or(G/G)or(C/C)or(A/) on 1#row with "A/A" and (T/T)or(G/G)or(C/C)or(A/A) on 2#row with "B/B". And then,from 4#row until 10#row i want to use logical replacement if each row contain "T/G/C/A" like 1#row it should be replaced with "A",and if each row contain "C" it should be replaced with "B".

Here is the result that i want:
1# T/T >>> 1# A/A
2# C/C >>> 2# B/B

4# T/T >>> 4# A/A
5# T/C >>> 5# A/B
6# T/C >>> 6# A/B
7# T/C >>> 7# A/B
8# C/C >>> 8# B/B
9# T/T >>> 9# A/A
10# T/T >>> 10# A/A


is there any logical function that i can use?
Thank you in advance.. :D