Think about that. In the early days of developmental biology, we didn’t even know whether there was differential gene activity or not; it was considered a reasonable possibility that all the genes were just doing their work, whatever it was, all the time in every cell, and that differences between cells emerged farther downstream, in biochemical interactions. But they knew this was an important question. They knew that we had to look at the activity of individual genes…they just didn’t have the tools yet. So it was back to hacking up embryos and trying to infer causes from aberrations.I used to teach this stuff in the 1980s and I certainly agree with PZ that you need to understand molecular biology and gene expression.
The change emerged gradually, but there were a couple of watershed moments where everyone looked up and noticed that hey, we do have ways of looking at genes directly. One was the work of Ed Lewis, a most excellent geneticist who used the tools of genetics to look directly at mutations that caused changes in fly morphology, in the 1960s. This was amazing stuff — the papers he wrote were beautiful and complex and very, very genetical — but it was written in a language that most developmental biologists of the day were unprepared to read. They were genetics papers. But I think they laid a foundation: if you want to do development, you’d better learn about genetics.
The second big event was the saturation mutagenesis screen of Christiane Nusslein-Volhard and Eric Wieschaus, about 20 years later. This work was also built on an understanding of genetics, but also used the tools of molecular biology. It was another lesson: if you want to do development, you’d better learn about molecular biology.
When it came time to write my first textbook I incorporated the examples I had used in class. The first ones I described were: the early to late switch in gene expression in bacteriophage T4, sporulation in Bacillus subtilis, and the genetic switch in bacteriophage lambda. These were well-studied examples from experiments carried out in the 1970s. They teach fundamental concepts in developmental biology and they have an additional advantage; namely, they get students thinking about species that aren't animals.
These are still excellent examples that are well-understood at the molecular level. They are much easier to understand than Drosophila or plants. Unfortunately, we've educated an entire generation of developmental biologists who have never heard of these elegant examples.
Is this a good thing or a bad thing? Do students need to know the real history of developmental gene expression as worked out by scientists who studied phage and bacteria?