Final answer:
Once the pair rule genes have gone, other genes and signaling pathways take over to refine and specify the boundaries between segments at the wingless engrailed boundary.
Step-by-step explanation:
Once the pair rule genes have gone, the wingless engrailed boundary undergoes changes. The pair rule genes, such as engrailed, play a crucial role in dividing the body into segments during early development. These genes determine where the boundaries of each segment will be. However, after the pair rule genes have fulfilled their role, additional genes and signaling pathways take over to further refine and specify the boundaries between segments.
For example, in Drosophila (fruit fly), once the initial segments have formed due to the actions of pair rule genes, the segment polarity genes become active. These genes further establish and maintain the boundaries between segments by controlling the expression of specific molecules, such as Wingless and Hedgehog, along the boundaries. These molecules provide positional information to cells, guiding their development and ensuring the proper patterning of the segments.
Therefore, although the pair rule genes are no longer involved, the wingless engrailed boundary continues to undergo development and refinement through the actions of other genes and molecular signaling pathways.