chromatid

In this schematic diagram of a human metaphase chromosome, (1) refers to a chromatid: one-half of the two identical double helices of the already replicated chromosome, both joined together by the centromere (2). During cell division, the identical copies (together called a twin chromatidsister chromatid pair) are divided over the two daughter cells, each double helix then constituting a homologous chromosomechromosome in its own right. The short (3) and long arm (4) of the chromatid to the right are also marked.