The assembly of microtubules responsible for the movement of chromosomes during anaphase is called chromosomal segregation or chromosome segregation.

Here's why:

* Microtubules: These are protein filaments that form the spindle fibers. They are responsible for pulling chromosomes apart.

* Anaphase: This is the stage of mitosis where chromosomes are separated and move towards opposite poles of the cell.

* Chromosomal segregation: This refers to the process of separating sister chromatids (identical copies of a chromosome) and moving them to opposite poles of the cell.

So, the assembly of microtubules during anaphase is the mechanism that enables chromosomal segregation, ensuring each daughter cell receives a complete set of chromosomes.