Final answer:
The left gonadal vein drains into the left renal vein, and the right gonadal vein drains into the inferior vena cava, due to the asymmetrical positioning of the inferior vena cava in the body.
Step-by-step explanation:
The left gonadal vein drains into the left renal vein, while the right gonadal vein drains into the inferior vena cava. This is because the gonadal veins, which include the ovarian veins in females and the testicular veins in males, follow a different path on each side of the body due to the position of the inferior vena cava primarily to the right of the vertebral column and aorta. This anatomical difference results in the left side's veins being generally longer than those on the right.