After the pairs of chromosomes are aligned, anaphase I begins. During this stage, the microtubules, or spindle fibers, pull the homologous chromosomes apart and move them to opposite ends of the cell.
Its called Anaphase when Chromosomes pull apart
During the cell cycle, it skips the whole process in the cell cycle to produce a cell, which causes errors within the cells and produce more of these errors. This how cancer occurs.
It is intended to increase immunity against that antigen back to protective levels, after memory against that antigen has declined through time.