A thread formed by the longitudinal division of a *chromosome
. During the S phase of the *cell cycle
, the DNA of the chromosomes replicates and the protein components of *chromatin are synthesized. As chromatin becomes condensed in *mitosis
, the chromosomes can be seen to be divided along their length, with the exception of the centromere, into two chromatids. In *meiosis
chromatids do not become apparent until the diplotene stage of the first prophase. Each is structurally a complete chromosome. During anaphase of mitosis and the second division of meiosis, when the centromeres divide, chromatids are separated to become the chromosomes of the daughter nuclei.