Molecular evidence Flashcards
What is the molecular evidence?
Later, following technological advances, BX-C was cloned and analysed.
What was discovered about BX-C which wasn’t as Lewis had proposed?
BX-C only had 3 transcription units, not as many as Lewis has thought.
What are the 3 transcription units?
- Ubx - PS5-14
- Abd-A - PS7-14
- Abd-B - PS10-14
Broad, overlapping domains. Expressed progressively more posterior.
What happens if Abd-B is mutated?
PS4-9 still develop normally but PS10-14 develop as PS9.
How does this still fit with Lewis’ model?
Lewis’ mutations fell within the regulatory control elements of the 3 transcription units above.
We can still see that the most posterior acting gene is what determines PS identity.
What did Lewis fail to predict?
He failed to predict that regional variation in level of gene expression would play a role.
The genes are expressed over multiple PS, need a way to distinguish individual parasegments. Ubx determines if PS is PS5 or PS6, but different level of Ubx determines which one. High level of Ubx is PS6, low level is PS5.
This regional variation is caused by regulatory elements for each parasegment. This is where Lewis’ mutations were. Not all are cis-regulatory elements, can also include regulatory RNAs which interact with polycomb proteins to repress Ubx - PS5.
What do HOM genes target?
Work with realisator genes that function to form specific tissues in segments.
