Final answer:
During metaphase of mitosis, sister chromatids align in the middle of the cell along the metaphase plate, held together by cohesin proteins, becoming highly visible and ready for the subsequent separation.
Step-by-step explanation:
The phase of mitosis where the pairs of sister chromatids align themselves in a single row along a plane halfway between the poles is called metaphase. This critical stage of cell division involves all of the chromosomes aligning themselves on what is known as the metaphase plate, or the equatorial plane, which is the name for the plane through the center of the spindle. The sister chromatids are tightly bound together by cohesin proteins, and at this stage, the chromosomes are maximally condensed and are highly visible under a microscope.
During metaphase, the microtubules of the mitotic spindle, extending from opposite poles of the cell, are attached to the kinetochores of each sister chromatid. It's the tension provided by these microtubules that ensures the chromatids are properly aligned before being separated in the subsequent phase, anaphase. This precise alignment is crucial for the equal distribution of genetic material to the two daughter cells.