Answer:
DNA replication
Step-by-step explanation:
For the most part of a cell's cycle, each chromosome has only one chromatid.
Before entering meiosis, a diploid cell (which contains a set of chromosomes from one parent and another set from the other parent) first doubles its DNA, and the cell will start division with each chromosome having 2 sister chromatids.
During meiosis I homologous chromosomes (the maternal and paternal sets) separate, and during meiosis II the sister chromatids separate. As a result, 4 daughter cells with half the original diploid chromosome number and one chromatid per chromosome are produced.