Pattern genes, in other words, are genes that contribute to cell memory.
They are expressed very early, and only for a very short period of time, but pattern characteristics survive indefinitely, and somehow, therefore, a cell keeps a “memory” of what they did. We could even say that, after the brief expression of its genes, pattern only lives in the memory space of a cell.
Pattern does not account for the whole of cell memory, because there are many other characteristics of determination which have long lasting effects, but it is certainly an important part of that memory. The discovery of the pattern genes, in conclusion, can also be regarded as the discovery of the first genes of cell memory.

Hints from developing neurons

The embryonic development of the nervous system is one of the most interesting processes of ontogenesis, and its study has also been one of the richest sources of information on the strategies that embryos adopt to solve their problems (Bonner, 1988; Edelman, 1988).
The first phase of neural development begins when a strip of ectoderm is induced to become nervous tissue by the underlying mesoderm, and comes to an end when neuroblasts complete their last mitosis, an event which marks the “birth” of a neuron. The extraordinary thing is that all that a neuron will do in its whole life is determined by its birth, and more precisely by the time and by the place of its birth. These two parameters leave an indelible mark in the cell, and somehow therefore they must physically be recorded in a true organic cell memory.
The second phase is a period during which neurons migrate to the places of their final destination, places that they “know” because somehow they are “written” in the memory of their birthtime and of their birthplace.
The third phase of neural development begins when neurons reach their definitive residence. From this time on, the body of a neuron does not move any more but sends out “tentacles” that begin an exploration journey in the surrounding space.