CHROMATIDS
Chromatid is one of copies of a chromosome, which is formed as the result of its duplication during the resting stage. Chromatid serves as an operating unit in mitosis. Chromatids of a mother chromosome (sister chromatids) become independent daughter chromosomes, while moving apart to the poles of the cell.
In the resting stage of meiosis sister chromatids of homologous chromosomes make pairs (conjugation) and form a structure of four chromatids. As this takes place, the process of section exchange is possible, either between sister chromatids or non-sister ones (genetic recombination, crossing-over).