I used genome sequence of Callorhinchus milii (elephant shark) to predict tbx4 gene by GeneWise software. My result contains a region of continuous N within the last exon as below: "CTATGGCAGCTGTGGAGTCCAGACCATGGNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNACCACGGCCATGATGCCACACCTGCCCGGGTTGCCCGCACAGAGCCCC". This gene aligned to the forward strand of scaffold NW_006890100.1 .
The record of Callorhinchus milii tbx4 protein in NCBI skippd the N region and its flank sequence above. [https://www.ncbi.nlm.nih.gov/protein/632958148]
The flank of skippd squence is as below: CCC[P]CCC[P]GTC[V]GCC[S]CCC[P]CTATGGCAGCTGTGGAGTCCAGACCATGGNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNACCACGGCCATGATGCCACACCTGCCCGGGTTGCCCGCACAGAGCCCCCAG[Q]CCG[P]CCT[P]TGC[C]GAC[D]
Was this sequence treated as a new intron? Or any other reason.
