The answer is anaphase.
Ron is obviously observing cell division - mitosis. Mitosis consists of four phases - prophase, metaphase, anaphase, telophase and cytokinesis.
1. Prophase: Chromatin in the nucleus condenses and chromosomes pair up
2. Metaphase: Chromosomes line up at the center of the cell. The sister chromatids are joined together.
<u>3. Anaphase: The sister chromatids separate from each other to the opposite sides of the cells.</u>
4. Telophase and Cytokinesis: Membrane forms around each set of chromosomes on two opposite sides of the cells and cell divides into two identical daughter cells.
<span>Therefore, sister chromatids being are pulled to the opposite ends of the cell in anaphase.</span>
