X0206 3 2020-06-11 0 0001733294 Generation Bio Co. GBIO 0001814308 Angelino Mark D. C/O GENERATION BIO CO., 301 BINNEY STREET CAMBRIDGE MA 02142 0 1 0 0 Chief Operating Officer Common Stock 283077 D Common Stock 169846 I See Footnote Stock Option (right to buy) 0.60 2028-01-04 Common Stock 100096 D Stock Option (right to buy) 4.60 2029-04-01 Common Stock 123761 D Stock Option (right to buy) 5.16 2030-03-04 Common Stock 84597 D Stock Option (right to buy) 5.16 2030-03-04 Common Stock 84596 D The securities are directly held by the Mark D. Angelino 2020 Qualified Annuity Trust, or the Trust. Mark D. Angelino is the settlor and trustee of the Trust, and the Trust is for the benefit of Elizabeth I., Emily A., John P., and Matthew R. Angelino. The reporting person may be deemed to beneficially own the shares of common stock owned by the Trust. The option was granted on January 5, 2018. The shares underlying the option vest over four years, with 25% of the shares vested on January 5, 2019 and the remaining shares vesting in equal quarterly installments thereafter. The option was granted on April 2, 2018. The shares underlying the option vest over four years, with 25% of the shares vested on April 2, 2019 and the remaining shares vesting in equal quarterly installments thereafter. The option was granted on March 5, 2020. The shares underlying the option vest in full upon the date on which the Board of Directors of the Issuer determines that the Issuer has dosed the initial patient in its first clinical trial, provided that such event occurs on or before July 1, 2023. The option was granted on March 5, 2020. The shares underlying the option vest over four years, with 25% of the shares vesting on March 5, 2021 and the remaining shares vesting in equal quarterly installments thereafter. Exhibit Index: 24.1 Power of Attorney /s/ Jennifer Elliott, Attorney-in-Fact 2020-06-11