This multi-series line chart visualizes gene expression trends across patient IDs, comparing three variables: Gene X Expression, Gene Y Expression, and Age. Using D3.js v7’s `d3.line()` and `d3.scaleLinear()`, the visualization renders three colored paths with circles marking every twentieth data point. The code loads CSV data via `d3.csv()` with `d3.autoType`, displays axes with `d3.axisBottom` and `d3.axisLeft`, and includes a custom legend. Styled with SVG and CSS, the chart applies a white background, rounded corners, and a subtle shadow.