FAC Ex. 3: DNA sequences

# DNA sequences

You're working in a scientific laboratory that specialises in DNA research. Cool!

Each sequence of DNA is made up of four bases: A, C, G and T. Your job is to count how many times each base appears in a particular sequence. You quickly get bored of doing this by hand and decide to write a program to do it for you.

You have the following sequence:

`"GCAACTCTCTATTGTGCCGGAAGTTAATATGCAAAGAGTAATTTCCCATCCCCACTACCGAATCCCTGACCAACCGCCTTCTTCAGGGTGATTACGTGCTAAGCTTATTAGCGCTCTCTTTTCCGATTCACTGTTCAAGATCGTCATTTTCGGGACCATTCCTTGATTCACACACTGAACGATTATGAGGTGTATACGAAACGGGTAGAGGCCCGCAAATGCGTCCTCGATACAGATGCTCGGGTCTGTTCCTGCACGGGCACGTAAACAGCGTGTTAAGGGAGAAAGTGTGAGTGTGAAGATGAATTAAAGGCTTATCAGCCACGGCTTCAAAGACTATAGCAACGCAGAGGAACCGAGCATTTCCATCCCAGCTCATGGTAATTTACTACGGGAGCTAACGCCAGAGGTAATATTTCTG    TCTGGCAGGTTTTATTAGCCGGGTGGGAGGGAGGAAGGAGTTGAAACTCGTTACCCAATTACTCGAAGGTGTACTATTACTTCTTTGGAGATCAACTGCAGTTTGCTTGGTAACACTCACATATAAATTGTGTACTGGGTCCCATTACTTTTTCTAGGGAGTAATTAAGTTATCCCTTAGCGAATATGATGCGGCTTTGGCTTTTGGCTTAACTACCCGAAAACCAGTCATGGCGTGCTACTTAAGAGGTCCCTAGTTACGTGCGCCAGGCTTGATCACCTGTGCAATAAACGCTAGCTCCACCCGATCTTATCAAGATCGATCACTATCCCTACGCCTTCAGAGGCCATGAGACGACAGCTCTGTCGTTCGCAGCCCTTTACACTGAATGCTGTGCGACCACGGATCTTTACTACGTGAT    ATAGATAATTTTATAATCGAGACCATCATTGCGTCTTTTCGTTTCGCACTATGCCCTTAACACGCACCCGCCTAGATCGAACAAAGGCGCGCGGAAATCCAGCTGGTACCTCTTTATGAAAATCGTGCGGGCGACGCCATAGAGAGTAAATCGTTTGA"`

Write a program that counts how many times each of the bases appears in the string.

## Expected results

A: 258
C: 241
G: 228
T: 273

## Extension

Now your boss asks you to work out how different two sequences are. Extend your program so that it accepts two DNA sequences and returns the difference in their base counts.

For example, given the sequence above and this new sequence:

`"CGCAAGCCTCTATGAGTGTTACTAACCACCTCCTGAGCGTTTCGTAGCCTGTCAACTTGCGGATCGGTGATGGCGTCTATGTTGCCCAGTCCCGCCCCCCATCAAATCAGACATACTATAATTTCTGTAAAGTAACAACACCTTTTCAGGGTCGGACGTGAATGTACGATTACATCGCTAGCATCATTACAGACGATGCATTGTCCTTGAGACAAAACTCGTGGTATACCCTTACGATCCCAGTGACAACAAATTCCATACAAGCTACGACGGACCCCTACCAACACTACCTTCAAGGAGCACGCAGTTAAAGCAACGAGCGGTTCAGACCTCCATGGTTATACTACGACTAAACACAGGTATCTATTAGTTTCGTTTCCATGAGAGAATTATGTTGCAAGCATGTGGTCCTCTATGCGTC    AAGGATGAGATAGCTGTTAGTTCATTTTATTGTTGGCCACCTGATGATTCACGTTTCGCCGAAATTCAGGCATTAACGCTAAAAAATGTTCTCTGTATTTTTTGTTCTGTGGCAATGTATAGCCTCGACTCCGGCAGACCAGGGAACGTTCTTGAAACTAAAGCACGCTGCTTCTAGGGGGGCATGCGTGTTATCGCCTTCAAGGAATTTCAGACAGGGGCAGTATCAGAGCATCGGCCACCTCGACAATTCCGTGTACTAGGCGGGCCACCATCGTCATGAGTGGAACACTTTTGGCGTATAATGTTCAATTAATCAGAGCCCTTGAGGTCTGTAGTCAGAATATGGGTTTAGTGACCTTCTGTCATGCCGAACGCGCCTCCTCCTAATTATTGGTCGTATGTCAATTAGACCCGTGATA    TTGCCTAATTACATCTGCGTCAGAGCCAAAGTGGAGCGCCAGGCTGAACACCCCTGCACAATCTACCCTAAGAACCACTTTAAGTGTGGAATCATCAACTTAATAGTGCGCCGTAACGTACCCCAACCTTCATCCTGTCCAGAGCGTTTCAATCTGCC"`

The second sequence's results should be:

A: 261
C: 255
G: 214
T: 270

And your program should return the differences like so:

A: 3
C: 14
G: 14
T: 3