Final answer:
Mitotic steps can be distinguished by observing the presence of spindle fibers, chromosome condensation, alignment, and the separation of sister chromatids during different stages of mitosis.
Step-by-step explanation:
Different mitotic steps were distinguished based on chromosome observation primarily by the presence of spindle fibers, and other characteristics, such as the condensation state of the chromosomes, their alignment at the metaphase plate, and by looking at the separation behavior of the sister chromatids. For example, during prophase, the chromosomes begin to condense and become visible, while the nuclear envelope breaks down. In metaphase, chromosomes line up at the center of the cell, and spindle fibers attached to kinetochores become evident. Anaphase is characterized by the separation of sister chromatids and their movement towards opposite poles. Indeed, the presence of spindle fibers is crucial as attachment of the mitotic spindle fibers to the kinetochores is characteristic of prometaphase. Each stage of mitosis has distinct events that allow cytologists and researchers to identify the current phase under the microscope.