C. Complexity of the genome

The total number of human genes identified by from the Human Genome Project—approximately 25,000—is much less than originally expected, considering the complexity of humans. However, it appears that most of our mRNA can be spliced (cut) and reassembled in alternate ways, giving rise to many more mRNAs and proteins than are encoded in our genome. Scientists believe that up to 60% of human genes can undergo alternative splicing of their mRNAs.¹ After mRNA is transcribed from DNA in the genome, introns are cut out (a process called splicing), leaving only intact coding sequences called exons. In addition to splicing out introns, the remaining mRNA can undergo further splicing. The sequences that are spliced can differ depending on which tissue the mRNA is located in and what job the resulting protein must perform.