Determination

In human embryos, immature cells that can form any tissue become progressively committed to a certain mature cell type through a two-step process, specification and determination.

The first step of specification results from a cell's location in the embryo, like where it lies on the dorsal, ventral axis and signals produced by it's neighbors. These positional elements expose a cell to a unique combination of factors that started down a developmental pathway such as neural formation.

If such specified cells were to be removed from the embryo and introduced to a neutral environment, like a dish containing basic growth medium, they would still go on to form their committed cell type, here neurons.

However, if proteins or other factors are added, cell fate can be altered so structures specified to form neurons could be redirected to yield another tissue like skin.

The continued action of positional factors within an embryo cause specified cells to enter the second stage, determination. Contrastingly, if determined cells are removed and inserted into a non-neutral setting, like a new embryonic area with different signals, they will still form neurons. Cell fate isn't changed.

Thus cells are gradually driven to a certain tissue type through the sequential action of specification and determination before they finally differentiate to form mature cells like neurons with distinct features.