Synthesis on a Cellular Level DNA in Eukaryotes resides in the cell's nucleus , but proteins are translated outside the nucleus. The length of all coding regions must be a multiple of three - however coding regions can be split over multiple exons. Which Complicate Gene Prediction Gene transfer mechanisms often introduce extra copies of genes into genomes, which then diverge through evolution. Distinguishing broken pseudo-genes from working genes is a difficult problem. Exons can be separated by several thousand bases.
Genes can overlap each other, appear in different reading frames and on different strands.
Exons can be assembled in multiple ways through alternative splicing . The traditional way to find genes was to do it in the laboratory. One method is to extract and sequence RNA, since most RNA is expressed to code for proteins. A problem with such laboratory methods is that relatively few genes tend to dominate the population of expressed sequences, and hence one discovered duplicates instead of new genes. Directly sequencing proteins is a difficult procedure, but is becoming easier through mass spectrometry.