Suggests simple mechanism for changing only the timing of gene action without requiring changes in control of gene expression or in nature of gene product. Potential importance for this type of heterochrony A. longer genes take longer to appear as gene products. This directly influcences relative timing of expression and can present different embryonic environment within which genes act. Not known what limits exist to controlling timing by alterations of intron length. First ten cycles require 8 min each, with only 3 min as interphase for transcription.
Subsequent cycles take longer and allow expression of long genes.
Unfinished transcripts are aborted at the end of the cell cycle and restarted anew in the next cycle. Thus changes in transcription time can cause disproportionate delays in expression by exceeding interphase duration for several cleavages. Abridged knirps-like with introns removed to yield 3 kb gene appears as protein during cycle 13. In systems like Drosophila where pattern formation is controlled by cascade of transcriptional regulation, there could be major phenotypic effects.