The average length of a S. cerevisiae gene is 1.6 kb (with a corresponding 1.5 kb mRNA), 1.5 for fungi in general (1.5 kb mRNA), 11.3 for fruitflies (2.7 kb mRNA) and 16.6 for mammals (2.2 kb mRNA). This exciting info (and more) can be found in the book'Genes V' by Benjamin Lewin. Oxford University Press, New York.