I'm reading my developmental biology textbook and I don't understand this concept. I can see how concentrations of Eve and Ftz determine each parasegment. However, I don't understand why the length of one parasegment isn't equal to the length of one segment on the actual embryo. Parasegments and segments are staggered from eachother.

Could anyone clarify?

Edit: I've gone back and re-read a bit. Is this staggering because parasegments are established while the embryo is still syncytial? So parasements are established, and afterwards cell division begins. But the daughter cells cant line up perfectly with the parasegments so segments and parasegments end up a bit staggered.

Edit2: Bit more reading. I think I got it. After parasegment establishment by Ftz/Eve, further segment polarity genes Engrailed and Wingless are expressed, with Engrailed expression being induced by either eve/ftz. The posterior side of the first engrailed cell determines where the boundary for a segment will be determined.

Can anyone confirm?

the image from my textbook


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