The two halves of a double chromosome structure are called chromatids.

Here's a breakdown:

* Chromosome: A long, thread-like structure that carries genetic information in the form of DNA.

* Chromatid: One of two identical copies of a chromosome that are joined together by a centromere.

* Centromere: The constricted region of a chromosome where the two chromatids are attached.

During cell division, the two chromatids separate, forming two new chromosomes, ensuring that each daughter cell receives a complete set of genetic information.