Exons are gene fragments whose DNA sequence after transcription is found in mature mRNAs. This part of the gene is most often coding.
The size of the exons in the genomes follows a log-normal distribution, with an average length of about 150 nucleotides, knowing that in eukaryotes, each gene contains several exons and introns (an average of 8) so the size is 8*150 = 1200 bp.
Question 2:
Introns are fragment of a gene located between two exons. Introns are present in immature mRNA and absent in mature mRNA. "Non-coding" fragment of the gene.
The introns average in a gene is 3365 bp including 3'UTR and 5'UTR and intermediate introns.
