Intron‐delay and the precision of expression of homoeotic gene products in Drosophila

It is suggested that the time taken in transcribing the large introns within homoeotic transcription units will reduce the quantity of mature transcript synthesised per nuclear division cycle. This could provide an additional level of control that would affect the ratios of fate‐determining gene products to each other. Determination of regional fate depends on both the large domains of homoeotic genes and the small, serially repeated domains of segmentation genes. As a consequence, each row of cells along the anteroposterior axis of the embryo could be assigned a precise, and unique, fate. This precision is apparently not dependent on cell lineage discontinuities.