During prophase, DNA condensed into X-shaped structures called

During prophase, DNA condensed into X-shaped structures called chromosomes.

Explanation:

The first step of the mitotic cell division is prophase. The main activity taking place during initial mitotic cell division - prophase is separation of the parent cell nuclear genetic material into two identical daughter cells.

Initially, the dense complex of chromatin fibers constituted by the DNA strands and proteins condense. This leads to coiling of the chromatin fibers making it more compact.

Chromosomes now become visible and replication of chromosomes takes place. This forms sister chromatids together which forms an X-shaped structure because they are joined in the center by the centromeres.