This review summarizes key candidate genes related to insulin metabolism (INS, INSR, IRS-1), the hypothalamic-pituitary-ovarian axis (LHβ, LHCGR, FSHR, GnRHR, AMH, AMHR2, KISS1, CAPN10), steroidogenesis (CYP11A, CYP17A1, CYP19A1, CYP21, 17β-HSD, SHBG, AR, STAR), and other clinically relevant mechanisms such as obesity, lipid metabolism (PPARG, VDR, FTO), and follicular development (ACE). This evidence concerns the gene CYP21A2 and Obesity.