14 mutant causes cell line to undergo more mitotic divisions before differentiation. Thus delayed onset of differentiaton. In organism with large degree of automous cell fate specification, invarint cleavage pattern, and eutely these changes have potentially major phenotypic effect. Growth occurs for same period as in larger mice but at greatly reduced rate. Drosophila RNA polymerase transcribes approx.
Differences are almost entirely due to length of intron.
Time of initiation of transcription is identical and rates of transcription are same but time of appearance of gene product is radically different. 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.