How come theres 1 smell per neuron

The “one OR per olfactory sensory neuron” constraint is not enforced by a single magic repressor. It is a control-system design: make “turning any OR on” slow, rare, and stochastic, then make “once a functional OR protein exists” trigger a fast, global stop signal that shuts the door behind the winner. Reviews often summarize this as “slow chromatin-mediated activation + fast negative feedback.” (annualreviews.org)

I’ll build it from the zygote forward, and I’ll be explicit about what each named protein is doing.

Start state from the zygote: why ORs do not accidentally turn on everywhere
In the zygote and early