1. Determine the codon usage for a DNA sequence

- Create a string containing a DNA sequence
- In a for loop
  - use the function substr ($seq, $offset, 3) to extract codons
  - store each codon and the number of times it has occurred in a hash
- Report the codon usage


2. Create a report of the expression levels and sequences of genes expressed in liver.

- There is a tab delimited file of  expression data.
- This file contains the following information:
GeneID, tissue the gene is expressed in, expression level, and gene sequence.
- Open this file script using open().
- In a loop:- 
	- Read a line in the file 
	- remove the "\n" at the end of the line
	- split the line on tabs using split (/\t/ , $line)
	- Store the data on each line in 3 different hashes as described below

hash	  key	    	value
%tissue	  GeneID	tissue
%expr	  GeneID	expression level
%seq	  GeneID	sequence

- Now search the %tissue hash for genes that are expressed in liver. Make a list of the GeneIDs corresponding to these genes.
- create a report of the GeneID and expression level of these genes