The point along the length of homologous chromatids where they remain held together to form a chromosome.
The structure that holds two strands of DNA together after replication until metaphase of mitosis is the centromere. The centromere is a region of the chromosome where the two sister chromatids are held together and is essential for proper chromosomal segregation during cell division.
A chromatid is one of the two identical copies of DNA making up a duplicated chromosome, which are joined at their centromeres, for the process of cell division (mitosis or meiosis). They are called sister chromatids so long as they are joined by the centromeres.