The replicas of chromosomes that form during prophase are called sister chromatids.

Here's why:

* Chromosomes are made up of DNA and are the structures that carry genetic information.

* Prophase is the first stage of mitosis (cell division) where the chromosomes condense and become visible.

* Sister chromatids are identical copies of a chromosome that are joined together at the centromere. They are created during the S phase (DNA replication) of the cell cycle.

During prophase, the sister chromatids remain attached and are eventually separated during anaphase, when they move to opposite poles of the cell.