I was reading through some of my old notes from 335, and it is mentioned that “for LOF in double mutants, the phenotype that is observed is the one more downstream therefore it has a stronger effect” .. so I think Dr. Kalas might have made a mistake in class about the dorsalization/ventrilization of the drosophilla in the week 3 lectures (pg 15) …
I think she mentioned that the dorsal mutant was a LOF and toll mutant was a GOF, however looking at my 335 notes, I think that both of the mutants may be a LOF mutant and therefore the phenotype that is seen is due to the gene/protein that is more downstream.
Looking at the artist’s drawing of the pathway, if dorsal was a LOF mutant and toll was a GOF mutant, then in a double mutant of dorsal and toll, we should get a ventralized embryo… So my main confusion here is that how is the embryo dorsalized when toll is always active and dorsal has lost its function …
🙁
Edit: Question resolved
All resolved? In 335 you might have been looking at double mutants where both mutations were LOFs…
If you have Toll that’s always active (GOF), everywhere (as opposed to only in the ventral part), then you are “forcing” dorsal to always be active, everywhere, instead of just in the dorsal part. That will cause a centralized embryo (or, maybe lateralized). However, if your GOF Toll is in combination with a LOF of dorsal (e.g. there may be no dorsal at all), then it does not matter of Toll is working everywhere all the time, because it cannot force dorsal to go and do its job and say “here is the ventral side”…. The single mutant LOF dorsal won’t make an ventral side (i.e. will be dorsalized), and the same will be true for the GOF Toll and LOF dorsal). In other words, in order for Toll to have any effect, dorsal needs to be present and wild-type. Let me know if you have more questions! 🙂