During early embryonic development, the fate of cells can be specified in various ways, leading to different developmental outcomes. One experimental approach to understanding this is by removing a set of cells from an early embryo and observing the effects on the resulting organism. If the adult organism lacks a structure that would normally be formed by those cells, this indicates a specific mode of specification.

This phenomenon most commonly points to autonomous specification, a process where the fate of each cell is predetermined by intrinsic factors, such as localized cytoplasmic determinants in the egg. In autonomous specification, cells independently follow their developmental program regardless of their environment. Hence, if these cells are removed, their specific structures will not form because no other cells can compensate for their loss. This mode of development is typical of mosaic embryos.

In contrast, conditional specification (also called regulative development) allows surrounding cells to change their fate to compensate for lost or damaged cells, often resulting in normal development even when some cells are removed.

Morphogenic specification is associated with development guided by morphogen gradients—diffusing signals that provide positional information to cells, influencing their fate based on concentration thresholds. This is more about spatial patterning than direct cell removal effects.

Syncytial specification involves the early embryo being a multinucleate cell (syncytium), with nuclei specifying fate through gradients of cytoplasmic determinants without distinct cell boundaries, as seen in insects like Drosophila.

Given the experimental outcome where removal of cells leads to absence of the corresponding structure, the embryo likely exhibits autonomous specification.

Therefore, the correct answer is:

(1) autonomous specification

This article clarifies how embryonic specification mechanisms influence developmental outcomes and explains the significance of experimental cell removal in determining the mode of specification. It highlights the crucial role of autonomous specification in maintaining fixed developmental fates that are independent of surrounding cells.