The cell-cycle control system initiates chromosome segregation only after has occurred

metaphase

Explanation:

The cell cycle control system initiates chromosome segregation only after metaphase has occurred.

At metaphase, the chromosomes of a dividing cell align at the equator to form what is known as the metaphase plate. Each chromosome gets engaged by spindles from the opposite sides of the poles at the kinetochore of the centromere.

Thereafter, the cell proceeds to the anaphase stage during which the shortening of the spindle fibers pulls the chromosome apart into sister chromatids and this eventually causes the sister chromatids to start migrating to opposite poles of the cell.

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.