Microexons difficult to recognize using computational genefinding methods exons, A list of selected documented microexons is available. Very small or microexons, pose special problems for gene annotation. The even confound the alignment of cDNA and genomic sequences. Furthermore because microexons are very often the site of alternative splicing, an understanding of how they are recognized (and regulated) is key to understanding gene expression.Microexons A list of selected documented microexons is available. Very small exons, or microexons, pose special problems for gene annotation. They are difficult to recognize using computational genefinding methods, and can even confound the alignment of cDNA and genomic sequences. Furthermore, because microexons are very often the site of alternative splicing, an understanding of how they are recognized (and regulated) is key to understanding gene expression