The factor that significantly affects metaphases on a slide during the slide-making process is cell density. The density of cells in a sample can directly influence the visibility and quality of metaphases observed in cytogenetic analysis. When cell density is appropriate, there will be a higher likelihood of observing a sufficient number of cells in the metaphase stage, which is crucial for accurate chromosome analysis. High cell density may lead to overcrowding on the slide, making it difficult to distinguish individual metaphases, while low cell density might not yield enough metaphases for analysis.
Other factors listed, such as chromosome number, sample age, and microscope quality, also play roles in cytogenetic studies but do not specifically address the immediate requirements during the slide preparation process. For instance, chromosome number is essential for understanding genetic conditions but does not impact the slide preparation itself. Sample age can affect cell viability, influencing the quality of metaphases; however, it is not directly involved in how cells are distributed on the slide. Microscope quality is critical for viewing metaphases but does not impact their arrangement or concentration on the slide during preparation. Thus, the cell density is the primary factor that directly affects the presence and assessment of metaphases during this crucial part of the cytogenetic analysis